[Federal Register: November 14, 2000 (Volume 65, Number 220)]
[Rules and Regulations]
[Page 68511-68560]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr14no00-19]
[[pp. 68511-68560]] Ergonomics Program
[[Continued from page 68510]]
[[Page 68511]]
adverse health effects occur, a point advanced by several in their
testimony to the docket (e.g., United Parcel Service, Ex. 500-197, pp.
I-68; Vender attachment to UPS post-hearing comments, Ex. 500-118, page
17). Dr. Hadler opined that ``whenever a relationship between exposure
and effect is not linear (not monotonic), you can be sure there are
confounders, * * *.'' (Hadler attachment to UPS post-hearing comments,
Ex. 500-118, page 4). He offered no evidence in support of this
assertion, and in fact there is no requirement in epidemiology that the
relationship must either be linear or monotonic. OSHA has relied on
non-linear dose-response relationships in other health standard
rulemakings (see Formaldehyde, 54 FR46168, Cadmium 57 FR 42101).
Second, most exposure-response relationships do not indicate a
single exposure level that unambiguously differentiates risk from no
risk. This is especially true if exposure is treated as continuous and
the relationship fits a straight line through the origin, in which case
each small increment in exposure increases the probability of an
adverse health outcome and, extrapolated downward, there may be no
discernable point without excess risk above the zero exposure level.
Note that in this regard U.P.S. criticized OSHA for the assumption
that, in fact, UPS had made: ``OSHA has falsely assumed that any
increment of human muscle usage is harmful, * * *.'' (United Parcel
Service, Ex. 500-197, pp. I-68).
On the other hand, when exposures have been categorized and are
ordinally associated with risk of disease, it can be argued that the
first exposure level where an elevated risk is observed above baseline
represents an appropriate point for a permissible exposure level (at
least until subsequent studies clarify whether there is still excess
morbidity occurring below that level). This type of approach was taken
recently by the American Conference of Governmental Industrial
Hygienists (2000), which used essentially the same epidemiologic
evidence available to OSHA--with its variety of exposure metrics--to
determine the proposed new Threshold Limit Value for
occupational hand activity level (see Exs. 38-162, DC-387).
Several authors have called attention to the complexity of the
process of utilizing exposure-response data for quantitative risk
assessment in the multi-dimensional domain of physical ergonomics
(e.g., Armstrong et al., 1993: Ex. 26-1110; Burdorf et al., 1997: Ex.
500-121-13; Frank et al., 1996: Ex. 502-407; Kilbom, 1999: Ex. 38-406;
Viikari-Juntura et al., 1999: Ex. 500-121-73). OSHA finds that it is
reasonable to conclude, as these experts have done, that there is a
need for continuing study of those relationships and interactions,
while at the same time, that it is appropriate to implement the
scientific knowledge in hand in order to reduce the risk of work-
related MSDs.
In the preamble to the proposed rule (64 FR 65768), OSHA presented
the results of several studies that provided evidence for positive
trends between exposure to biomechanical risk factors and the
prevalence or incidence of MSDs. Three commenters critiqued twelve of
these studies, claiming a variety of design or methodological flaws in
the studies, computational errors in the studies, or that OSHA misused
some of the data (Exs. 30-276, 500-79, 32-241-4). The comments are
those of Dr. Steven Moore, Professor, Environmental and Occupational
Health, Texas A&M University (Ex. 30-276), Marathon Ashland Petroleum
LLC (Ex. 500-79), and Gibson, Dunn & Crutcher (Ex. 32-241-4). Marathon
Ashland Petroleum LLC includes Dr. Moore's comments as an Appendix.
Gibson, Dunn & Crutcher summarize the critiques of several experts,
whose statements are attached to their comment. OSHA responds to all
these comments below.
Dr. Moore and Gibson, Dunn & Crutcher criticized the study on risk
factors for CTS by deKrom et al., (1990, Ex. 500-41-28). They claim
that the study does not account for psychosocial factors and that it is
methodologically flawed in relying on self-reported information about
duration of exposure, rendering the results meaningless. With respect
to the lack of analysis on psychosocial factors, OSHA acknowledges that
this case-control study, with cases mostly of hospital outpatients and
controls from the general population, did not examine or control for
psychosocial factors. However, OSHA finds nothing in the design and
analysis of this study that would invalidate the statistically
significant positive associations among work related physical factors
and CTS that the study did find. The authors concluded that activities
with a flexed wrist or with an extended wrist (exposure-related
increased ORs) were risk factors for CTS. Dr. Moore criticized the
duration analysis used to estimate exposure-response as a function of
time, claiming that the survey questionnaire instrument for collecting
exposure information was unreliable. OSHA responds that with little
information about the survey questionnaire in the published paper, the
agency cannot determine the reliability. However, from a description in
the paper of the blindness with which the survey was administered, OSHA
believes that such an imperfect exposure measurement instrument would
yield non-differential exposure misclassification. Such non-
differential misclassification would bias both the ORs and the slope
toward a finding of no increasing trend. The fact the deKrom et al.
study found statistically significant ORs for each incremental number
of weekly hours of activities with extended or flexed wrist separately,
plus finding a statistically significant exposure-response trend for
both duration variables, despite the negative bias, provides strong
evidence that the effect is real. This finding is further strengthened
by the final analysis of de Krom et al. which used a multiple
regression model simultaneously containing both duration of ``flex''
and ``extended'' wrist activities as variables, with both variables
found to be statistically significant for duration-of-exposure-response
trends (Ex. 500-41-28, pg. 1108). The finding of joint statistical
significance of collinear variables when simultaneously modeled
increases confidence in the significance of the separate variables.
OSHA also responds to the criticism that ``in a conclusion that
would devastate OSHA's attempt to redesign the American office, [deKrom
et al.] found no significant risk of CTS related to typing.''OSHA notes
that of the 156 cases of CTS, only 12 cases reported any work-related
typing at all. In a case-control study such as this with only 12 cases
exposed to typing, the statistical ability to determine a significant
result is very small. Either a different study recruitment procedure or
a much larger sample size would be required. With respect to another
criticism by Gibson, Dunn & Crutcher on the apparently spurious finding
of an association of CTS with varicosis in men, the authors reported
this result of their analysis for the scientific world to contemplate,
but found it inconsistent with that of other authors (Ex. 32-241-4).
Dr. Moore also criticizes OSHA's use of the MSD prevalence study by
Luopajarvi et al., (1979, Ex. 26-56) used as part of the agency's
determination of causality for hand/wrist tendinitis. Dr. Moore claims
the study's poor exposure assessment and lack of statistical
comparisons provide poor support. In response, OSHA notes that the same
exposure assessment methods were used in the study comparisons between
the assembly-line packers and the shop assistants, so that the
differences should be unaffected. OSHA also notes that
[[Page 68512]]
these comparison showed that the assembly-line packers had a highly
statistically significant (p0.001) increased prevalence of (1)
syndromes found in the neck, shoulders and elbows; and (2) muscle-
tendon syndromes in the hands (p0.001). The most common neck syndrome
in this study was tension neck and the most common shoulder disorder
was humeral tendinitis. For hands, Luopajarvi et al. noted the
prevalence of tenosynovitis/peritendinitis at 53% in the assembly-line
packers, but only 14% in the shop-assistants (who endured prolonged
standing, but otherwise physically light work). For the assembly-line
packers the authors noted especially the repetitive motions at a high
speed, and fingers and hands constantly used at the pace of the
machine, up to 25,000 cycles per workday. For these packers the authors
also noted difficult static muscle work, extreme work positions of the
hands, and difficult lifting. OSHA believes that this study provides a
good comparison between similar demographic groups, and that it
provides good evidence that work-related physical stress factors were
causing shoulder and upper extremities injuries.
Dr. Moore also claims that errors in the evaluations of two other
studies are materially related to the NIOSH's and OSHA's conclusions
(Ex. 30-276, pg. 2). With respect to the study by Kuorinka and
Koskinen, he criticizes NIOSH for not specifically mentioning the
``non-positive'' finding of no evidence of association of with time
spent in deviated wrist postures per day. OSHA responds that the
Kuorinka and Koskinen study did not specifically mention peritendinitis
and tenosynovitis in its analysis, only the total complex of muscle-
tendon syndrome. Their definition of muscle-tendon syndrome used in
this study came from an accompanying article they coauthored in the
same journal (see Ex. 26-1218); the definition included syndromes of
the shoulder and elbow, along with the wrist and hands. Every one of
the seventeen (out of 93) manual workers with muscle-tendon syndrome
also had tension neck syndrome, but none was specifically identified as
having either peritendinitis or tenosynovitis (Ex. 26-639). While Dr.
Moore is correct that Kuorinka and Koskinen found no correlation
between the number of signs in the wrist and the deviation load of the
wrist joint (1979, Ex. 26-639). OSHA finds too few details in the
analysis for any conclusions with respect to peritendinitis and
tenosynovitis.
Dr. Moore also criticizes the NIOSH 1997 (Ex. 26-1) review for its
failure to include the findings of a second study, Armstrong et al.,
(1987, Ex. 500-41-4) in NIOSH's evaluation on the effect of posture for
hand/wrist tendinitis. Dr. Moore claims that NIOSH rated the Armstrong
et al. study as high quality for other physical risk factors (i.e.
force and repetition, for which the study found highly statistically
significant associations) but didn't include the study at all in the
discussion of the effect of posture. Armstrong et al. reported no
significant associations for differences in posture ``comparing the
percentage of the time spent in various postures between jobs in which
there were workers with tendinitis and those in which there were no
workers with tendinitis'' (Ex. 500-41-4). Dr. Moore claims that this
omission by NIOSH and OSHA is an error in evaluation and that this
error ``would likely have a material impact on the conclusion'' (Ex.
30-276).
OSHA has considered Dr. Moore's claim about NIOSH's evaluation of
the Armstrong et al. study and has concluded that while Dr. Moore is
correct in his claim that Armstrong et al. found no associations with
the posture variable stated above, there is simply not enough detail in
the publication to weight that study highly with regard to the posture
variable. With this study group Armstrong et al. found a highly
statistically significant odds ratio of 29.4 (p0.001) for high force/
high repetitiveness hand/wrist motion compared with a low force/low
repetitiveness motion group. These groups appeared well defined and
well studied with respect to force and repetitiveness, with 652 workers
divided fairly evenly among the four groups increasing the statistical
power to detect an effect if one exists. However, no detail is given
for the posture analysis, only a short paragraph result (Ex. 500-41-4).
To study this same highly force- and repetitiveness-stressed group for
the effect of posture differences on hand/wrist tendinitis, (and CTS,
see Silverstein et al., 1987, Ex. 26-34, and comment in Ex. 32-241-4,
pg.143) would appear to be quite difficult, considering the proven
effect of force and repetitiveness as risk factors in this worker
group. Silverstein et al. (1986) studying essentially the same group,
discussed postures, stating:
(W)rist postures required on a job are often determined by the
height of the work station with respect to the location of the
worker. * * * to test this hypothesis the job of each worker in a
job would have to have been videotaped and analyzed. This was not
done in this investigation. * * * Awkward postures (wrist deviation,
flexion, hyperextension, and finger pinching) * * * were not
controlled for in this investigation. (Ex. 26-1404).
OSHA concludes that NIOSH was correct in not considering the
Armstrong et al. (Ex. 500-41-4) and Silverstein et al.1986 and 1987,
(Exs. 26-1404, 26-34) study further for posture with this particular
study group.
Gibson, Dunn & Crutcher also criticize OSHA's omission that the
Armstrong et al., study ``found no significant association between * *
* vibration and [hand/wrist tendinitis] (Ex.32-241-4, pg. 140). OSHA
responds that the Armstrong et al., 1987, (Ex. 500-41-4) publication
provided less information about vibration in the study group than it
did about posture, and that apparently it was not a well studied factor
in this group.
Dr. Moore also criticizes the ``NIOSH and OSHA reviews [for]
inappropriately generaliz[ing] results of some studies beyond the
constructs used to measure or categorize MSD risk factor [i.e., force
and repetitiveness]'' (Ex. 30-276, pg. 2-3), singling out Armstrong et
al. (Ex. 500-41-4) and Silverstein et al., 1987, (Ex. 26-34). OSHA has
considered this comment and disagrees with Dr. Moore. Most authors
define risk factors slightly differently and the NIOSH analysis had to
categorize the slightly different definitions into categories. OSHA
believes this categorization does not detract from either the NIOSH
analysis or the ability to generalize that force and repetitiveness are
etiologically related to hand/wrist tendinitis. In fact, OSHA believes
that the different studies' abilities to detect significant
associations using different definitions actually make the overall
results more generalizable.
Gibson, Dunn & Crutcher, also criticize the Silverstein et al.,
1986 study of hand wrist cumulative trauma disorders (CTDs, Ex. 26-
1404, and by implication Exs. 26-34 and 500-41-4) for being
methodologically flawed, specifically citing recall bias and observer
bias as leading to an overestimation of the associations between risk
factors and health effect (Ex. 32-241-4, pg. 142-143). They also cite
the study's cross-sectional design, the omission of a number of jobs
from the investigation, and lack of analysis on non-biomechanical
factors as serious flaws.
OSHA has considered this criticism of the methodology, but
disagrees with the characterization that a cross-sectional design
cannot establish causation. In another section of this preamble, OSHA
discusses the value of all the studies together in forming a database
to determine causality. OSHA also notes
[[Page 68513]]
the claims of bias in this study, but agrees with the Silverstein et
al., 1986 study authors who found significant positive and publishable
associations between hand wrist CTDs and high force-high repetitive
jobs:
The findings in this investigation may also have underestimated
the prevalence of hand wrist CTDs in several ways. Firstly, subject
selection was limited to active workers. those away from the job
with CTDs at the time of evaluation (potentially severe cases) would
not have been available for study. Secondly, the one year seniority
criteria for subject selection excluded those who might have had
CTDs and transferred before one year as well as those with CTDs but
not on the job for at least one year. The finding that hand wrist
CTDs were negatively associated with age and years on the job
support the argument of selection/survival bias in the study
population [which would underestimate the effect] (Ex. 26-1404, pg.
784).
Gibson, Dunn & Crutcher criticize the study of shoulder pain in
shipyard workers (welders and steel plate-workers) by Herberts et al.,
1984, (Ex. 26-51), for methodological flaws, including cross-sectional
design, and the lack of demographic matching between the exposed and
control groups. (Ex. 32-241-4, pg. 142). They also criticized OSHA for
not recognizing what Herberts et al. did, have ``chronic shoulder pain
is * * * common in people not necessarily active in arduous physical
work.'' (Ex. 26-51, pg. 167). OSHA responds that the Agency does
recognize that people other than those in HPW have shoulder pain; that
recognition allows researchers, OSHA and other analysts to compare the
prevalence of shoulder pain in workers doing HPW to that in workers not
so engaged, in order to estimate the contribution from HPW. Herberts et
al. also did this and concluded that ``Rotator cuff tendinitis
constitutes a major problem in people with arduous occupations, i.e.,
shipyard welders (PR=18.3%), and steel plate-workers (PR=16.2%).'' By
contrast, of the 57 clerks in the comparison group only one (1.7%)
reported this disorder. Of this highly statistically significant
difference, Herberts et al., note:
Since the clerks are on an average older than the other two
groups, there would be a higher likelihood of age-induced tendinitis
in this [clerks] group. However, the hypothesis is that those with a
high physical workload have tendinitis to a greater extent than
normal. (Ex. 26-51).
Gibson, Dunn & Crutcher also criticize OSHA's use of the Punnett et
al., 1991 (Ex. 26-39) study of back disorders and nonneutral trunk
postures in automobile assembly workers. The study is criticized as
methodologically flawed in that it is a case-control study that does
not consider non-biomechanical variables (Ex. 32-241-4, pg. 140).
Gibson, Dunn & Crutcher quote the authors' own cautions of the
limitations of such a design, which is necessarily retrospective in
recalling exposures and pre-existing conditions. OSHA acknowledges the
limitations of such as design. However, OSHA considers the design,
conduct, and analysis of this study quite persuasive--in terms of
strength of association, temporality, and exposure-response--in the
overall determination of causality of BT and LBP; see OSHA's section on
back disorders in this preamble. The authors in their publication
conclude:
Back disorders were associated with mild trunk flexion (OR=4.9
(p5% C.I. 1.4-17.4), severe trunk flexion (OR=5.7, 95% C.I. 1.6-
20.4), and trunk twist or lateral bend (OR=5.0, 95% C.I. 1.6-21.4).
the risk increased with exposure to multiple postures and increasing
duration of exposure. (Ex. 26-39, pg. 337).
Gibson, Dunn & Crutcher also criticize Dr. Punnett's more recent
study (1998, Ex. 26-38) of upper extremity disorders in vehicle
manufacturing, as being methodologically flawed in that it is a cross-
sectional design and does not include an analysis of the relative
importance of psychosocial factors. OSHA has considered this comment
and disagrees. Even though this study is cross-sectional, OSHA
considers it well-conducted and analyzed. Using a primary exposure
score relating to responses to psychophysical exposure items, Punnett
found both statistically significant PRs and significant exposure-
response relationships for both (1) shoulder and upper arm disorders
and (2) wrist and hand disorders. The results were consistent when the
analyses were done both for the symptom cases and the physical
examination cases. The authors concluded that ``musculoskeletal
disorders of the upper extremities were strongly associated with
exposure to combined ergonomic stressors.'' (Ex. 32-241-4) Gibson, Dunn
& Crutcher also criticize OSHA's use of the prospective study by Liles
and Deivanayagam, 1984 (Ex. 26-33) on job severity index (JSI) for the
evaluation and control of lifting injury of the back. The JSI is a
function of lifting frequency of task, maximum required weight of lift,
adjusted capacity of the individual, and total lifting frequency.
Criticism of the study focuses on a potential bias which Gibson, Dunn &
Crutcher call a ``nocebo effect'', a bias due to differential reporting
of pain symptoms by the subjects, knowing that their symptoms are being
monitored. OSHA responds that such a potential bias is purely
speculative, and, in any case, does not explain either the increasing
injury rate, the cumulative disabling injury rate or the cumulative
severity rates seen with increasing JSI. (Ex. 26-33, pgs. 690-691).
Gibson, Dunn & Crutcher also criticize the study by Snook et al.,
(1978, Ex. 26-35) on three preventive approaches to low back injury.
The study is criticized as being methodologically flawed in that it is
a cross-sectional study which looks solely at biomechanical risk
factors, and cannot establish causation. However, Gibson, Dunn &
Crutcher also quote several portions of the article that it wants OSHA
to recognize: (1) that most cases of industrial back injury have no
known cause, and recovery occurs before any cause is ever found, (2)
some workers never suffer from low back pain regardless of their type
of work, and others seem to get it in spite of what they do; and (3)
``low back injuries are usually not serious; four out of five workers
suffering from low back injuries return to the job within three
weeks.'' (Ex.32-241-4). OSHA responds that this Snook et al., case-
series study of 191 low back injuries is of limited usefulness in
determining causality, but it does suggest that low back injury is
associated with excessive manual handling tasks. OSHA also acknowledges
the general apparent truthfulness of statement (2), by Snook et al.,
but can find no reference for it in the article. Statement (1) of Snook
et al., references a 1970 published article and a 1971 editorial. There
is more recent science available. Statement (3) cites one 1966 study as
its reference.
Gibson, Dunn & Crutcher also criticize a study by (1992, Ex. 26-36)
on low back and neck/shoulder pain in construction workers. They claim
that the study is methodologically flawed in that it is cross-sectional
in design, limiting its ability to show causality. At the same time
they criticize OSHA for failing to discuss the study's findings of
positive associations between LBP and both psychosocial factors and
age, as well as the finding(s) of no significant association between
sitting posture and LBP (and severe LBP). OSHA responds that with
respect to sitting (>4 hours) posture and the Holmstrom et al. (Ex. 26-
36) finding of no significant association with either LBP or severe
LBP, both NIOSH (Ex. 26-1, pg. 6-47) and OSHA (see Table on back
studies considered) do consider the finding of this study as ``no
association'' for SWP and LBP. With respect to specific psychosocial
factors being significant in this analysis, OSHA concurs. However, the
discussion of psychosocial factors
[[Page 68514]]
by Holmstrom et al. fails to mention whether or not the multiple
regression model used also found the physical risk factors
simultaneously statistically significant with these data, which would
suggest that physical and psychosocial factors are independent risk
factors (Ex. 26-36, pg. 667).
4. Comments on the Role of Individual and Non-Work Factors
In their posthearing testimony, Gibson, Dunn and Crutcher assert
that:
In developing its unfounded assertion that biomechanical
workplace factors play a predominant role in the development of
MSDs, OSHA has also ignored a great number of scientifically valid
studies establishing that non-work-related factors, such as genetic
predisposition, age, general health, smoking, social activities, and
psychosocial factors exert a greater influence than biomechanical
factors on the development of MSDs (Ex. 500-118).
Other commenters also expressed concern about the role of non-work
factors in the etiology of MSDs (e.g., Exs. 30-1722, 60-2037, 30-4184,
30-3077, 30-1352, 30-4130, 30-3922, 30-3114, 30-3354).
While some commenters tended to lump individual factors along with
psychosocial factors, these two types of factors are clearly separate
and distinct. OSHA has separated its discussion of individual factors
from that of psychosocial factors, and has fully addressed comments on
psychosocial factors later in this part of the Health Effects section.
In this section OSHA presents it's response to comments in the record
on individual factors, sometimes called ``personal'' factors. The
factors that are discussed in the literature include age,
susceptibility, either by genetic predisposition or medical conditions,
and other factors that may be thought of as those that modify the
capacity of individuals to perform work.
The above post-hearing comment (Ex. 500-18) makes two claims:
(1) that OSHA ignored an entire body of literature relevant to this
rulemaking, and
(2) that had OSHA not ignored this body of literature, it would
have come to an opposite conclusion than that reached by OSHA, i.e.,
that these factors ``exert a greater influence'' presumably than
biomechanical risk factors, on the development of MSDs.
OSHA, in fact, did not ignore the literature on individual factors.
On the contrary, OSHA introduced the appendices to the proposed Health
Effects section with a discussion of ``Individual Factors and
Epidemiology of Work-Related Musculoskeletal Disorders,'' stating that:
The multifactorial nature of MSDs requires a discussion of
individual factors that have been studied to determine their
association with or influence on the incidence and prevalence of
work-related MSDs. These factors include age (Guo et al., 1995;
Biering-Sorensen et al., 1983; English et al., 1995; Ohlsson et al.,
1994); gender (Hales et al., 1994; Johansson, 1994; Chiang et al.,
1993; Armstrong et al., 1987a); anthropometry (Werner et al., 1994;
Nathan et al., 1993; Heliovaara, 1987); physical activity
(Holmstrom, Lindell, and Moritz, 1992; Baron et al., 1991; Craig et
al., 1998); strength (Chaffin and Park, 1973; Chaffin et al., 1977;
Troup, Martin, and Lloyd, 1981); cigarette smoking (Finkelstein,
1995; Owen and Damron, 1984; Svensson and Andersson, 1983; Kelsey,
Golden, and Mundt, 1990; Hildebrandt, 1987); and alcohol, caffeine,
and vitamins (Nathan et al., 1996, Keiston et al., 1997). In
addition, psychosocial factors have been associated with upper-
extremity and back disorders (Ex. 27-1, p. I-1).
OSHA has stated elsewhere that it relied on two major reviews of
the evidence for work-relatedness of MSDs available at that time,
NIOSH's ``Musculoskeletal Disorders and Workplace Factors: A Critical
Review of the Epidemiologic Evidence for Work-Related Musculoskeletal
Disorders of the Neck, Upper Extremity, and Low Back'' (Bernard, 1997;
Ex. 26-1) and the National Research Council/National Academy of
Sciences' ``Workshop on Work-Related Musculoskeletal Injuries: The
Research Base'' (Ex. 26-37). OSHA believes that it was appropriate to
place great weight on these two sources, as they are comprehensive
reviews of recent peer-reviewed scientific literature conducted by
highly-reputable and independent groups of scientists expert in their
respective fields.
To the extent that the studies reviewed by NIOSH considered
exposure to nonoccupational physical activities, such as
nonoccupational VDT use, hobbies, second jobs, and household activities
that might increase risk for MSDs, NIOSH included this information in
its review, and acknowledges that:
a number of factors can influence a person's response to risk
factors for MSDs in the workplace and elsewhere. Among these are the
following: age, gender, smoking, physical activity, strength,
anthropometry.
The literature, as reviewed by NIOSH (NIOSH, 1997; Ex. 26-1): on
each of these individual factors is summarized here:
Age: The prevalence of MSDs increases as people enter their working
years. By the age of 35, most people have had their first episode of
back pain (Guo et al. 1995, Ex. 26-1474; Chaffin 1979, Ex. 26-1489).
Once in their working years (age 25 to 65), however, the prevalence is
relatively consistent (Guo et al. 1995, Ex. 26-1274; Biering-Sorenson
1983, Ex. 26-843). Musculoskeletal impairments are among the most
prevalent and symptomatic health problems of middle and old age.
Nonetheless, age groups with the highest rates of compensable back pain
and strains are the 20-24 age group for men, and the 30-34 age group
for women.
NIOSH acknowledges that age-related degenerative disorders may
result in decreases in musculoskeletal function, and loss of tissue
strength with age may also increase the probability or severity of soft
tissue damage. NIOSH also notes that:
Another problem is that advancing age and increasing number of
years on the job are usually correlated. Age is a true confounder
with years of employment, so that these factors must be adjusted for
when determining relationship with work. Many of the epidemiologic
studies that looked at populations with a wide age variance have
controlled for age by statistical methods.
However,
Several studies found age to be an important factor associated with
MSDs (Guo et al. 1995; Biering-Sorenson 1983; English et al. 1995;
Ohlsson et al. 1994; Riihimaki et al. 1989a; Toomingas et al. 1991)
others have not (Herberts et al, 1981; Punnett et al. 1985). [Ex.
26-1]
Riihimaki et al. (1989, Ex. 26-58) found a significant relationship
between sciatica and age in machine operators, carpenters, and
sedentary workers. Age was also a strong risk factor for neck and
shoulder symptoms in these same groups of workers (Riihimaki et al.
1989, Ex. 26-58).
When a study does not find a relationship between an increased risk
for MSDs and aging, lack of an observed relationship may be due to
``survivor bias.'' If workers who have health problems leave their
jobs, or change jobs to one with less exposure, the remaining
population includes only those workers whose health has not been
adversely affected at their jobs. As an example, in a study of female
plastics assembly workers, Ohlsson et al. (1989, Ex. 26-1290) reported
that the degree of increase in the odds of neck and shoulder pain with
the duration of employment depended on the age of the worker. For the
younger subjects, the odds increased significantly as the duration of
employment increased, but for the older ones no statistical change was
found with length of employment. The older women who had been employed
for shorter periods of time had more reported symptoms than the
[[Page 68515]]
younger ones, while older workers with longer employment times reported
fewer symptoms than younger workers. Ohlsson et al. (1989, Ex. 26-1290)
interviewed 76 former assembly workers and found that 26% reported pain
as the cause of leaving work. This finding supports the likely role of
a survivor bias in this study, the effect of which is to underestimate
the true risk of developing MSDs, in this case in the older workers.
Some studies report observing an increased risk for MSDs with age,
others do not. Where the effects of age have been controlled for in
studies, thus eliminating the influence of ``age'' in the equation, the
physical risk factors discussed here have been consistently shown to be
associated with the development of MSDs in exposed populations. This
means that, regardless of whether or not age plays a role in the
development of a particular MSD in a particular population, the
influence of physical risk factors is independent.
Gender Some studies have found a higher prevalence of some MSDs in
women (Bernard et al. 1994, Ex. 26-842; Hales et al. 1994, Ex. 26-131;
Johansson 1994, Ex. 26-1331; Chiang et al. 1993, Ex. 26-1117). A male-
to-female ratio of 1:3 was described for carpal tunnel syndrome (CTS)
in a population study in which occupation was not evaluated (Stevens et
al. 1988, Ex. 26-1009). However, in the Silverstein et al. (1985, Ex.
26-1173) study of CTS among industrial workers, no gender difference
could be seen after controlling for work exposure. Franklin et al.
(1991, Ex. 26-948) found no gender difference in workers' compensation
claims for CTS. Burt, Hornung, and Fine (1990, Ex. 26-698) found no
gender difference in reporting of neck or upper-extremity MSD symptoms
among newspaper employees using video display terminals (VDTs). Nathan
et al. (1988, Ex. 26-990; 1992, Ex. 26-988) found no gender differences
for CTS. In contrast, Hagberg and Wegman (1987, Ex. 26-32) reported
that neck and shoulder muscular pain is more common among females than
males, both in the general population and among industrial workers.
Whether the gender difference seen with some MSDs is due to
physiological differences or differences in exposure is unclear. One
laboratory study, Lindman et al. (1991, Ex. 26-976), found that women
have more type I muscle fibers in the trapezius muscle than men, and
have hypothesized that myofascial pain originates in these type I
muscle fibers. Ulin et al. (1993, Ex. 26-223) noted that significant
gender differences in work posture were related to stature and
concluded that the lack of workplace accommodation to the range of
workers' height and reach may, in part, account for the apparent gender
differences.
The fact that more women are employed in hand-intensive jobs and
industries may account for the greater number of reported work-related
MSDs among women. Bystrom et al. (1995, Ex. 26-897) reported that men
were more likely to have de Quervain's disease than women; they
attributed this to more frequent use of hand tools.
The reporting bias may exist because women may be more likely to
report pain and seek medical treatment than men (Armstrong et al.,
1993; Hales et al., 1994). Some studies have reported that workplace
risk factors account for increased prevalence of MSDs among women more
than personal factors (e.g., Armstrong et al. 1987, Ex. 26-1110;
McCormack et al. 1990, Ex. 26-1334). In a recent evaluation of Ontario
workers' compensation claims for repetitive strain injury (RSI), Asbury
et al. (1995, Ex. 26-250) reported a relative risk (RR) for female to
male claims ranging from 1.3 to 1.6 across industries. Within five
different broad occupational categories, females were approximately 2
to 5 times as likely to have a lost-time RSI claim. No information on
gender differences in hand-intensive jobs was reported. Many
researchers have noted that men and women tend to be employed in
different jobs.
Smoking. In the Viikari-Juntura et al. (1994, Ex. 26-873)
prospective study of machine operators, carpenters, and office workers,
current smoking (OR: 1.9; 95% CI: 1.0-3.5), was among the predictors
for change from ``no neck trouble'' to ``severe neck trouble.'' In a
study of Finnish adults aged 30 to 64 (Makela et al. 1991, Ex. 26-980),
neck pain was found to be significantly associated with current smoking
(OR: 1.3; 95% CI: 1.0-1.61) when the logistic model was adjusted for
age and gender. However, when the model included mental and physical
stress at work, obesity, and parity, then smoking (OR: 1.25; 95% CI:
0.99-1.57) was no longer statistically significant (Makela et al. 1991,
Ex. 26-980). With univariate analysis, Holmstrom (1992, Ex. 26-36)
found a prevalence rate ratio (PRR) of 1.2 (95% CI: 1.1-1.3) for neck/
shoulder trouble in ``current'' smokers vs. people who ``never''
smoked. But using multiple logistic regression, when age, individual,
and employment factors were in the model, only ``never smoked''
contributed significantly to neck/shoulder trouble.
While investigating reasons for higher compensation claims for CTS
in certain employee groups, Nathan et al. (1996, Ex. 26-882) evaluated
the effects of tobacco, caffeine, and alcohol on the prevalence of
median entrapment neuropathy at the wrist, CTS symptoms, and CTS
confirmed by nerve conduction studies among industrial workers
(nonclaimants and working patients referred for upper-extremity
symptoms) who volunteered for the study. Nathan et al. (1996, Ex. 26-
882) stated that greater use of tobacco combined with greater
consumption of caffeinated beverages and alcohol abuse was associated
with more median nerve slowing, more specific hand/wrist symptoms, and
more electrophysiologically confirmed CTS. However, the effects
explained only a small portion of the total risk.
Toomingas et al. (1991, Ex. 26-1019) found no associations between
multiple health outcomes (including tension neck syndrome, rotator cuff
tendinitis, CTS, or problems in the neck/scapula or shoulder/upper arm)
and nicotine habits among platers, assemblers, and white collar
workers. In a case/referent study, Wieslander et al. (1989, Ex. 26-
1027) found that smoking or using snuff was not related to CTS among
men operated on for CTS.
Several papers have presented evidence that a positive smoking
history is associated with low-back pain, sciatica, or intervertebral
herniated disc (Finkelstein 1995, Ex. 26-369; Frymoyer, Pope, and
Clements 1983, Ex. 26-950; Svensson et al. 1983, Ex. 26-1158; Kelsey et
al. 1984, Ex. 26-152); whereas other papers have found a negative
relationship (Kelsey, Golden, and Mundt 1990, Ex. 26-52; Riihimaki et
al. 1989, Ex. 26-997). Boshuizen et al. (1993, Ex. 26-81) found a
relationship between smoking and back pain only in those occupations
that required physical exertion. In their study, smoking was more
clearly related to pain in the extremities than to pain in the neck or
the back. Deyo and Bass (1989, Ex. 26-105) observed that the prevalence
of back pain increased with the number of pack-years of cigarette
smoking and with the heaviest smoking level. Heliovaara et al. (1991,
Ex. 26-959) only observed a relationship in men and women older than 50
years. Two studies did not find a relationship between sciatica and
smoking among concrete reinforcement workers and house painters
(Heliovaara et al. 1991, Ex. 26-959; Riihimaki et al. 1989, Ex. 26-
997).
Several explanations for the relationship with smoking have been
postulated. One hypothesis is that back pain is caused by coughing from
smoking. Coughing increases the abdominal pressure and intradiscal
pressure and puts strain on the spine. A
[[Page 68516]]
few studies have observed this relationship (Deyo and Bass 1989, Ex.
26-105; Frymoyer et al. 1980, Ex. 26-707; Troup et al. 1987, Ex. 26-
1307). The other mechanisms proposed include nicotine-induced
diminished blood flow to vulnerable tissues (Frymoyer, Pope, and
Clements 1983, Ex. 26-950), and smoking-induced diminished mineral
content of bone causing microfractures (Svensson et al. 1983, Ex. 26-
1158). Similar associations with diminished blood flow to vulnerable
tissues have been found between smoking and Raynaud's disease.
Strength. Some epidemiologic support exists for the relationship
between back injury and a mismatch of physical strength and job tasks.
Chaffin and Park (1973, Ex. 26-1115) found a sharp increase in back
injury rates in subjects performing jobs requiring strength that was
greater than or equal to their isometric strength-test values. The risk
was 3 times greater in the weaker subjects. In a second longitudinal
study, Chaffin et al. (1977, Ex. 26-1111) evaluated the risk of back
injuries and strength and found the risk to be 3 times greater in the
subjects without lower static strength. Keyserling, Herrin, and Chaffin
(1980, Ex. 26-970) strength-tested subjects, biomechanically analyzed
jobs, and assigned subjects to either stressed or non-stressed jobs.
Following medical records for a year, they found that job matching
based on strength criteria appeared to be beneficial. In another
prospective study, Troup, Martin, and Lloyd (1981, Ex. 26-1456) found
that reduced strength of back flexor muscles was a consistent predictor
of recurrent or persistent back pain, but this association was not
found for first-time occurrence of back pain.
Other studies have not found the same relationship with physical
strength. Two prospective studies of low-back pain reports (or claims)
of large populations of blue collar workers (Battie et al. 1989, Ex.
26-72; Leino, Aro, and Hasan 1987, Ex. 26-1142) failed to demonstrate
that stronger (defined by isometric lifting strength) workers are at
lower risk for low-back pain claims or episodes. One study followed
workers for 10 years after strength testing and the other followed
workers for a few years. Neither of these studies included precise
measurement of exposure level for each worker, so the authors could not
estimate the degree of mismatch between workers' strength and task
demands. Battie compared workers with back pain with other workers on
the same job (by isometric strength testing) and did not find that
workers with back pain were weaker. In two studies of nurses (Videman
et al. 1989, Ex. 26-1155; Mostardi et al. 1992, Ex. 26-986), lifting
strength was not a reliable predictor of back pain.
When examined together, these studies reveal the following: the
studies that found a significant relationship between strength and back
pain used more thorough job assessment analysis and focused on manual
lifting jobs. However, these studies only followed workers for periods
of 1 year, and whether this same relationship would hold over a much
longer working period remains unclear. The studies that did not find a
relationship, although they followed workers for longer periods of
time, did not include precise measurements of exposure level for each
worker, so they could not assess the strength capabilities that were
important in the jobs.
Anthropometry. Weight, height, body mass index (BMI) (a ratio of
weight to height squared), and obesity have all been identified in
studies as potential risk factors for certain MSDs, especially CTS and
lumbar disc herniation. Obesity seems to play a small but significant
role in the occurrence of CTS (see Section B.4.a). Anthropometric data
are conflicting, but in general indicate that there is no strong
correlation between stature, body weight, body build, and low-back
pain.
Few studies examining anthropometric risk factors in relationship
to CTS have been occupational epidemiologic studies; most have used
hospital-based populations that may differ substantially from working
populations. Nathan et al. (1988, Ex. 26-990; 1992, Ex. 26-989; 1994,
Ex. 26-517) have published several papers about a single industrial
population and have reported an association between CTS and obesity;
however, the methods employed in their studies have been questioned in
a number of subsequent publications (Gerr and Letz 1992, Ex. 26-384;
Mackinnon et al. 1997, Ex. 26-1309; Stock 1991, Ex. 26-1010; Werner et
al. 1994, Ex. 26-237). Several investigators have reported that their
industrial study subjects with CTS were shorter and heavier than the
general population (Cannon et al. 1981, Ex. 26-1212; Dieck and Kelsey
1985, Ex. 26-944; Falck and Aarnio 1983, Ex. 26-1122; Nathan et al.
1992, Ex. 26-989; Werner et al. 1994, Ex. 26-237; Wieslander et al.
1989, Ex. 26-1027).
Werner et al. (1994, Ex. 26-237) studied a clinical population
requiring electrodiagnostic evaluation of the right upper extremity,
patients classified as obese (BMI > 29) were 2.5 times more likely than
slender patients (BMI 20) to be diagnosed with CTS. These researchers
developed a multiple linear-regression CTS model (with the difference
between median and ulnar sensory latencies as the dependent variable).
The regression highlighted BMI as the most influential variable, but
still only accounted for 5% of the variance in the model. In Nathan's
(1994, Ex. 26-517) logistic model, BMI accounted for 8.6% of the total
risk; however, this analysis used both hands from each study subject as
separate observations, although they are not independent of each other.
Falck and Aarnio (1983, Ex. 26-1122) found no difference in BMI among
17 butchers with (53%) and without (47%) CTS. Vessey, Villard-
Mackintosh, and Yeates (1990, Ex. 26-229) found that the risk for CTS
among obese women was double that for slender women.
Nordstrom et al. (1997, Ex. 26-900), in a study of risk factors for
CTS in a general population, concluded that BMI is one factor that
seems to have a causal relation to CTS. These researchers found that
for each increase of one unit of BMI, about 6 pounds for the average-
sized adult, risk of CTS increases by 8%. Werner et al. (1997, Ex. 26-
718), in a study at five different worksites (four industrial, one
clerical), concluded that obesity (BMI > 29), industrial work, and age
were independent risk factors for median mononeuropathies. Their study,
which did not define specific work-related exposures, showed no
significant interaction between work activity and obesity. However, the
authors caution interpretation of the data and urge more investigation.
It has been suggested that relationship of CTS with BMI involves
increased fatty tissue within the carpal canal or increased hydrostatic
pressure throughout the carpal canal in obese persons compared with
slender persons (Werner 1994, Ex. 26-237).
Two other anthropometric risk factors, carpal tunnel size and wrist
size, have been suggested as risk factors for CTS; however, some
studies have linked both small and large canal areas to CTS (Bleecker
et al. 1985, Ex. 26-934; Winn and Habes 1990, Ex. 26-1029).
Schierhout et al. (1995, Ex. 26-403) found that short stature was
significantly associated with pain in the neck and shoulder but not in
the forearm, hand and wrist, or back, among workers in 11 factories.
Height was not a factor for neck, shoulder, or hand and wrist MSDs
among newspaper employees (Bernard et al. 1994, Ex. 26-842). Kvarnstrom
(1983, Ex. 26-1201) found no relationship between neck/shoulder MSDs
and body height in a
[[Page 68517]]
Swedish engineering company with more than 11,000 workers.
Examples exist where biomechanical or physical risk factors have
been labeled as individual factors. During the hearing for this
rulemaking, Dr. Niklas Krause mentioned two of these examples, the
first refers to people in the military who drive tanks, and found that
tall people have more back pain than short people. A very logical
explanation for the observation of increased back pain was provided by
Dr. Krause:
Well, if you have ever entered a tank, you know that it is not
constructed for very tall people. There is not much room in there.
[Tr. 1378]
And a second example, also provided by Dr. Krause:
And we have actually found in our bus drivers, too, and we
measured. We had their height and their weight. We found that an
ergonomic evaluation of the bus fleet showed that the buses that are
running in San Francisco were constructed for people--that is what
the ergonomics Professor Thompson from Sanford found out when he
looked at them--were constructed for people in the upper 10 percent
of the North American population.
You can imagine if you hire small people, Asians and women for
example, into that work force and put them on this bus that the fit
is bad. And actually, what we see is that over the years, the
percentage of small drivers drops on that work force rapidly.
When they enter, when people take the job, there is about 6
percent of drivers who are small, defined as * * * the lower half of
the population. * * * After one to five years, only 2.9 percent of
these small people are in the workforce. After six to ten years,
only 1.3 percent. And after eleven to fifteen years, only 0.4
percent. This is a statistically significant trend. And it clearly
shows you that people based on their smallness and misfit probably
had to leave the occupation. [Tr. 1378-1380]
When used to determine whether a correlation exists between
stature, body weight, body build and low back pain, anthropometric data
are conflicting, but in general indicate that there is no strong
correlation. Obesity seems to play a small but significant role in the
occurrence of CTS.
Genetics. Another type of factor that affects an individual's
capacity is genetic make-up. While the term ``genetic susceptibility''
is often heard; in reality both the amount of genetic information
involved in the response and the variability of possible responses are
vast and for the most part, not yet understood. The little bit of work
done in this area was done by Videman, and is covered in a brief
discussion in the section on the low back.
A worker's ability to respond to work factors may be modified by
his or her own capacity. The capacity to perform work varies with
gender and age, among workers, and for any individual over time. The
relationship between biomechanical risk factors, both inside and
outside the workplace, these individual as well as other factors and
the resulting risk of injury to the worker is complex, but not unique
to this OSHA standard.
For each of the ``individual factors'' discussed here, some studies
report observing an increased risk for MSDs, others do not. What they
have in common, is their ability to effect the capacity of individuals
independently from biomechanical risk factors. In other words, in those
studies where the effects of age, gender, smoking, etc. have been
controlled for, the physical risk factors discussed here have been
consistently shown to be associated with the development of MSDs in
exposed populations. This means that, regardless of whether or not age
plays a role in the development of a particular MSD in a particular
population, the influence of biomechanical risk factors is independent
from other associated factors. Furthermore, it has been demonstrated
repeatedly, that reducing these biomechanical factors in the workplace
results in reductions in the incidence of work-related MSDs.
The AFL/CIO found that the record provides some additional evidence
that individuals may vary in their susceptibility to developing certain
work-related MSDs, such as carpal tunnel syndrome, based on individual
factors including age, body weight and gender (Ex. 26-1, Ex. 26-37, Ex.
500-71-93). They also found that other evidence in the record indicates
that for back and neck pain or disorders, for example, no association
with age, gender, height or weight has been established (Ex. 500-71-24,
Tr. 1332).
The AFL/CIO point out that:
Obviously the underlying principle of ergonomics is to fit the
job to the worker, and so personal physical characteristics do come
into play when evaluating certain MSD risk factors. A worker who is
5'2" may have a much longer reach to an assembly line than her 6'0"
co-worker. But other than as relevant to evaluating exposure to
known risk factors, personal characteristics and differences in
susceptibility are irrelevant to this rulemaking. This regulation,
and all other OSHA standards, are designed to regulate risks that
are found in the workplace that may result in the development of an
adverse outcome (MSDs) in workers who are exposed to risk factors
which have been demonstrated to cause MSDs. The ergonomics
regulation is consistent with OSHA's responsibility to regulate
hazards which are present in the workplace. To shift the focus
toward personal characteristics, as some industry opponents have
argued, only clouds this issue by blaming the victims. [Ex. 500-218]
On this same subject, Dr. Frederick Gerr, Emory University (Tr.
1525-26):
Some will argue that personal factors, such as gender and body
weight, are the cause of these disorders among American workers,
rather than ergonomics hazards in the workplace. The fact that
personal characteristics can increase the risk for these disorders
in no way undermines the evidence that work has been clearly shown
to increase their risk as well.
The blame-the-victim approach to these disorders is both
scientifically and ethically bankrupt. Virtually all occupational
illnesses, including asthma, cancer, skin disease, peripheral and
central nervous system disorders, and many others, have causes that
extend outside of the workplace. This fact does not lessen the added
burden of disease that occupational exposures produce.
Non-Work Leisure Activities
The commenters (e.g., Exs. 30-2493, 31-324, 30-3368, 30-605, 30-
3783, Tr. 5073) also raise the issue of the relationship of ``non-
work'' to the development of MSDs. By this, OSHA assumes the reference
is to those activities such as nonoccupational VDT use, hobbies, second
jobs, and household activities, activities that may result in
additional exposure to biomechanical factors similar to that the
individual is experiencing at the workplace. If this assumption is
correct, then ``non-work'' may actually refer to exposure to the same
types of physical/biomechanical factors that may be additive to similar
workplace exposure.
And, while it is true that the physical/biomechanical risk factors
which increase the risk of MSDs at work can also be found outside of
work and may lead to MSDs (Ex. 500-71-93). However, according to Dr.
Nicholas Warren from the University of Connecticut (Tr. 1077-78):
It is very seldom the case that home risk factors are
encountered with the same intensity or the same duration as they are
encountered in the workplace.
On the same subject , the AFL/CIO (Ex. 500-218) notes:
Opponents of the standard, while arguing that there is no
evidence that physical factors at work cause MSDs, also
simultaneously argue that it is non-work leisure physical activities
which cause MSDs and that an OSHA standard cannot regulate adverse
health conditions and exposures to risk factors which are partially,
primarily or exclusively the result of non-work activities (Ex. 32-
241-4).
For most musculoskeletal disorder cases, ``workplace factors are
the predominant risk and it is upon these risks, obviously, that the
OSHA proposed rule focuses (Tr.1079). Other evidence in the record
confirms that there is little or no impact on the development of
MSDs related to the back from non-work
[[Page 68518]]
participation in sports, exercise, and leisure time physical
activity (Ex. 500-71-24, Ex. 500-71-32, Ex. 502-510).
The AFL/CIO also states:
Thus the record evidence suggests that the non-work exposures to
risk factors rarely, if ever, occur at the same frequency, duration
or magnitude as workplace exposures. Even where workers are exposed
to non-work risk factors off the job, it is important to point out
that this standard is designed only to decrease exposures to
biomechanic risk factors occurring at the workplace. An analogy may
be drawn to the risks of incurring hearing loss from excessive
exposure to noise. Exposure to noise at levels and durations which
can cause or contribute to noise-induced hearing loss can and do
occur both at the workplace as well as in non-work situations. While
these work and non-work exposures and risks of developing hearing
loss exist, OSHA's noise standard is confined exclusively to
addressing excessive noise exposures in the workplace. [Ex. 500-218]
And from Dr. Nicholas Warren, University of Connecticut (Tr.
1078-79):
When I work with an individual with, for instance, carpal tunnel
syndrome, carrying out forceful, repetitive tasks over most of a
nominal 40 hour work week and then often into another 10 hours of
voluntary overtime, it's painful to hear an insurer gleefully inform
me that this person bowls in a league on Saturday night. It is
equally painful to hear the worker blame him or herself by saying,
``That's probably because I knit,'' when, in fact, a clear objective
assessment of the workplace risk factors reveals that these are much
more important in the etiology of his or her disease.
OSHA concludes that, in general, each individual's capacity is
affected differently by many factors including some of those presented
here: age, gender, smoking, physical activity, strength, anthropometry,
genetic factors and activities outside the workplace. This is also true
in the more specific case of the development of work-related MSDs.
However, it is important to remember that exposure to biomechanical
factors in the workplace is independent of those factors that each
individual brings to the workplace, i.e., when the influence of
individual factors is controlled for in studies, effects due to
exposure to biomechanical factors are still observed . It is also true
that in the vast majority of cases, where exposure to biomechanical
exposures is high, the effects due to biomechanical exposures are far
greater than those associated with these types of individual factors.
5. Role of Psychosocial Factors in the Etiology of MSDs
The role of psychosocial factors in the etiology of MSDs was a
subject of much debate during the rulemaking. Many participants, in
particular the Chamber of Commerce (Ex. 500-188), Gibson, Dunn &
Crutcher (Exs. 32-241-4, 500-197), and several research and medical
scientists who testified on behalf of UPS (Exs. 32-241-3-2, 32-241-3-3,
32-241-3-5, 32-241-3-8, 32-241-3-12), criticized the proposed rule for
its failure to take into account the contribution of psychosocial risk
factors to MSD causation and exacerbation, believing that psychosocial
factors play a significantly greater role than do biomechanical risk
factors in the development of MSDs and the disabilities associated with
them.
Much of the scientific literature that addresses the etiology of
MSDs has examined aspects of the social and psychological environment
that may have a causal or moderating role in MSD development and
exacerbation. In this part of the Health Effects section, OSHA first
discusses what is meant in the literature by the term ``psychosocial
factors.'' Following this discussion, OSHA summarizes the expert
testimony of witnesses and rulemaking participants who have evaluated
the body of psychosocial literature as it relates to the work-related
risk of MSDs. Finally, OSHA presents its own literature review,
summarizing specific studies contained in the rulemaking docket that
have examined and compared the roles of biomechanical and psychosocial
factors in the etiology of MSDs, and summarizes several literature
reviews that have been published on this topic.
Definition of Psychosocial Factors
The study of psychosocial factors as it applies to the study of
work-related MSDs is surrounded by a measure of confusion because there
are several very different definitions of ``psychosocial'' used in
common and in technical parlance. Lack of clarity and consensus in
defining psychosocial factors was addressed by some researchers at the
public hearing (Tr. 867-868, 1306, 17443). There are three general
concepts of psychosocial factors that apply. Most researchers who have
examined the role of psychosocial factors in the etiology of MSDs have
emphasized the external aspects of the psychological and social work
environment that cause the worker to experience ``stress'', a condition
of chronic or prolonged arousal of the human ``flight or fight''
mechanisms that has been linked to a wide variety of negative health
outcomes, including MSDs. The primary aspects of the psychosocial work
environment include level of psychological job demands, level of worker
control over the job process, and level of social support received from
co-workers, supervisors and the organization. Some researchers focus on
additional conceptualizations of psychosocial exposures, including job
security, monotony, and job satisfaction (for example, Krause, 1998,
Ex. 38-242, Bigos, 1991b Ex. 26-1242). Psychosocial factors reflecting
these external aspects of the work environment have been the subject of
investigation in nearly all of the studies and literature reviews
discussed in this section.
As is the case with biomechanical risk factors, proposed exposure-
outcome relationships for psychosocial factors are multifactoral, i.e.,
several of these factors may be in play in any given situation, and may
combine and interact in complex ways that are difficult to study and
understand (Bongers et al., 1993, Ex. 26-1292, Bernard, 1997, Ex. 26-1
Warren et al., 2000a, b, Exs. 38-75, 38-73). It is unlikely that these
psychosocial workplace risk factors occur and act in isolation of
biomechanical risk factors (Tr. 868-869, 1264, 5942-5943, NIOSH 1997
(Ex. 26-1), NAS 1999 (Ex. 26-37)).
A growing body of literature also identifies aspects of
organizational structure, technology, policy, and culture as potential
contributors to occupational disease and characterizes them as
organizational risk factors (Shannon, et al., 1996, Ex. 26-1368, 1997,
Ex. 26-1369, Warren, 1997, Ex. 38-72, Warren et al., 2000a, Ex. 38-75).
Organizational risk factors are proposed as the underlying bases of
work design in the company; through their effect on work organization,
they determine levels of both psychosocial and biomechanical risk
factors experienced by employees. It is this common set of roots that
results in the strong co-variation of psychosocial and biomechanical
risk factors noted below. The second concept of psychosocial factors
that has been used in the literature relates to the internal
characteristics of the worker's psychological makeup that affect how
he/she appraises, processes and reacts to external biomechanical and
psychosocial factors, and thus moderates how these external factors are
experienced internally. There are studies demonstrating that individual
psychological factors can increase susceptibility to MSD development
and affect MSD recognition and reporting (Linton, 2000, Ex. 502-413,
NAS, 1999 Ex. 26-37). Emerging research sugg influence care-seeking and
disability than initial onset of disease (Linton, 1992, 2000, Ex. 502-
413 ests that internal psychological factors more strongly, Waddell &
Burton, 2000, Ex. DC-151-A). Some researchers and physicians combine
internal and external psychological factors in their
[[Page 68519]]
definition of psychosocial factors; for example, Dr. Raymond Bellamy,
an orthopedic surgeon testifying on behalf of UPS et al., included such
factors as dislike of job, recent poor performance evaluation,
depression and anxiety, hypochondriasis, and desire for narcotics in
his description of psychosocial factors (Ex. 32-241-3-3). Dr. Arthur
Barsky, also testifying on behalf of UPS et al., stated that
psychosocial factors (his use of the term conflates external factors
and internal psychological factors) ``exacerbate, perpetuate, and
maintain these [musculoskeletal] symptoms and amplify the disability
they engender'' (post-testimony comments, p.1, Ex. 500-118-1). Thus, it
is not always clear in the literature or in the testimony contained in
the record when the term ``psychosocial factors'' is being used to
refer to external psychological or social workplace factors, internal
psychological makeup of the worker, or both.
The third concept of psychosocial factors relates to aspects of the
legal, insurance and medical environment that influence a worker's
tendency to identify a particular constellation of symptoms as a
disease. At its most extreme, this definition is used to claim that
workers make up and fake disease, for ``secondary gain''. A broader
interpretation is the argument that these aspects of legal and medical
recognition and possible financial gain may subtly, even unconsciously
influence a worker's honest identification of symptoms as a disease and
predisposition to report it.
Although individual psychological factors or medical/legal factors
may affect MSD perception and reporting to a degree, it is unlikely
that they play a major causal role in the etiology of MSDs. This is
because the increased prevalence and incidence of MSDs seen among
workers who are highly exposed to biomechanical risk factors cannot be
adequately explained primarily by psychological factors given the
present state of the evidence. As the discussion in this Health Effects
section has demonstrated, the epidemiological, laboratory,
psychophysical, and intervention literature demonstrating quantifiable
links between biomechanical exposures and MSD outcomes is overwhelming.
Many studies have demonstrated substantial differences in MSD incidence
and prevalence between companies and industry sectors that correlate
strongly with the presence of physical risk factors (for example,
Franklin et al., 1991, Ex. 26-948, NAS, 1999, Ex. 26-37, see also the
Risk Assessment section (Section VI) of this preamble). Thus, it is
highly unlikely that an individual with psychological tendencies
towards negative reactions at work or tendencies to seek out care-
givers would preferentially select themselves into physically demanding
jobs. It is also impossible to imagine how prospects for secondary gain
would be differentially distributed into occupations or industry
sectors that involve highly physical work.
Consequently, this part of the Health Effects section focuses on
the large number of studies that have simultaneously examined the roles
of biomechanical risk factors along with psychosocial factors that
relate to external aspects of the psychological and social work
environment. These studies generally represent the most recent studies
of work-related MSDs in the literature.
Discussion of Testimony on the Psychosocial Literature
Based on these studies, the Chamber of Commerce (Ex. 500-188) and
Gibson, Dunn & Crutcher representing UPS, Anheuser-Busch, the National
Coalition on Ergonomics, and others (e.g., Exs. 32-231-4, 500-197,
32,435, 30-3346, Tr. 3655) were critical of OSHA emphasizing the role
of biomechanical risk factors over psychosocial factors in its
scientific literature review. For example, in their post-hearing brief,
Gibson, Dunn & Crutcher commented that
The science has shown that where psychosocial factors in
particular are considered, they generally overwhelm the weak and
inconsistent associations between biomechanical exposures and the
reporting of MSDs. Yet the * * * [A]gency dismissed the validity of
psychosocial factors in cavalier fashion * * * [Ex. 500-197, p. I-
33]
Similarly, the Chamber of Commerce stated that ``The Agency has
egregiously ignored each and every one of these indisputably relevant
factors * * *'' (Ex. 500-188), and explained the necessity for OSHA to
evaluate the role of psychosocial factors in the workplace:
* * * [D]etermining why individuals feel the need to report and/or
to seek medical care for such complaints is a complex problem
involving not only the physical exposures, but psychosocial factors
such as job satisfaction, ability to control the work environment,
interpersonal relationships at work, and the like * * * And, in the
vast majority of studies that have assessed whether biomechanical
workplace factors and psychosocial factors cause musculoskeletal
complaints, psychosocial factors are just as significant, or more
significant than, biomechanical factors. (Ex. 500-188, p. 41)
In addition, several research and medical scientists testifying on
behalf of UPS et al. stated in written or oral comment that the
scientific literature strongly supported that psychosocial factors play
a dominant role in the etiology of MSDs (Exs. 32-241-3-2,32-241-3-3,
32-241-3-5, 32-241-3-8, 32-241-3-12). For example,
Dr. Alf Nachemson concluded a review of the literature by stating
that
* * * [t]he research indicates that psychosocial factors are not
simply an overlay but rather an integral part of the pain disability
process that includes emotional, cognitive and behavioral aspects *
* * [T]here was strong evidence of the highest level that
psychosocial variables generally have more impact than biomedical or
biomechanical factors on pain disability.'' (Ex. 32-241-3-12, p. 13)
Dr. Norton Hadler stated in written comment that
Associations between disabling regional musculoskeletal symptoms
and psychosocial variables overwhelm and explain away any and all
associations with biomechanical exposures. (Ex.32-241-3-8, p. 18)
Taking a more moderate interpretation of the literature, Dr. Arthur
Barsky agreed that MSDs are not entirely a psychosocial problem;
however, he felt that ignoring them in designing intervention programs
can make the problem worse (Ex. 500-118-1, p. 1). At the public
hearing, he explained that
* * * [workers'] symptoms really are better understood as a social
communication, as a kind of non-verbal way of responding to
difficulties in the workplace--job dissatisfaction, role conflicts,
insecurity around the job, a whole variety of psychosocial work
conditions--and to hear these as a biomedical complaint is to
totally miss the point * * * What really concerns me, is * * * [that
complaints of MSD symptoms are] a kind of social communication * * *
a metaphor for life stress, for psychosocial distress * * * and the
response that too often is made to a symptom like that, is [an
inappropriate] referral to orthopedics. Tr. 17043-17044]
Dr. Barsky illustrated his point with an example of a widowed mother of
two worked two jobs and visited the emergency room of a hospital
complaining of tired feet [Tr. 17043-17044], and viewed the proposed
ergonomics standard as an inappropriate response to such an
``interpersonal communication'' (Tr. 17044).
Other scientists testifying on behalf of the UPS echoed the
conclusions reached by Dr. Nachemson in his literature review and Dr.
Bigos, who referred to
[[Page 68520]]
his groups Boeing study (Ex. 26-1241, 26-1242,26-1393) in contending
that low back pain (LBP) is primarily a psychosocial phenomenon (Exs.
32-241-3-2, 32-241-3-5). Other commenters also remarked on the
importance of psychosocial factors in the development of MSDs (e.g.,
Exs. 32-435, 30-3346, 30-3086, 30-536, 30-4046, 30-1070, Tr. 3655).
Many of OSHA's scientific witnesses disputed these interpretations
of the psychosocial literature, stating that the literature is not in
conflict with the causal relationship that has been demonstrated
between exposure to biomechanical risk factors and development of MSDs,
and that psychosocial factors had generally less of an influence than
biomechanical factors in these studies (Tr. 842, 874, 1087, 1206, 1364,
1537-1540). For example, Dr. Thomas Armstrong testified that
* * * [M]ore than a critical mass of epidemiological literature
shows that biomechanical factors are important predictors of the
occurrence of musculoskeletal disorders and the elevated risk of
harm.
In studies where we have included both psychosocial and physical
risk factors, the physical factors come out as the strongest
predictor. [Tr. 842]
Dr. Laura Punnett testified that ``* * * the impact of physical
exposures at work is beyond that explained by demographics, medical
history, psychosocial features of the work environment or other
factors'' (Tr. 874). Similarly, Dr. Nicholas Warren testified that in
studies that have measured both biomechanical and psychosocial factors
* * * we almost always find that both contributed. If you control
for psychosocial risk factors[,] which well-designed studies allow
you to do, you'll find a strong contribution from biomechanical risk
factors and that it generally, not in all workplaces, but in most
workplaces, is a larger effect than that of the psychosocial risk
factors. [Tr. 1087]
When asked whether he would agree with Gibson, Dunn & Crutcher's
statement in their pre-hearing submission that ``a majority of medical
experts who study the causes of MSDs believe most chronic workplace
pain is caused by psychosocial issues'' (Ex. 32-241-4, p. 36), both Dr.
Bradley Evanoff and Dr. Fred Gerr disagreed. Dr. Evanoff believed the
opposite was true, that ``the majority of people studying work-related
musculoskeletal disorders * * * feel that physical exposures are a very
strong risk factor'' Tr. 1358). Dr. Gerr stated that he was ``aware of
absolutely no basis in the medical or scientific literature that
[would] substantiate that statement'' (Tr. 1538). Both also strongly
disagreed (Tr. 1538-1539) with Dr. Hadler's statement in his written
testimony that psychosocial factors ``overwhelm and explain away any
and all associations with biomechanical factors'' (Ex.32-241-3-8, p.
18).
Several other researchers and medical scientists appearing at the
hearing on their own behalf disagreed with the UPS witnesses
assessments that psychosocial factors predominate in the etiology of
MSDs (Tr. 2838, 2840, 7857-7858, 9504, 9880). Dr. George Piligian of
the Mt. Sinai Center for Occupational and Environmental Medicine, when
asked whether it was appropriate for OSHA to emphasize the role of
biomechanical factors in its proposed rule given the evidence on
psychosocial factors, responded with an analogy:
* * * [Suppose] a person is thirsty and has come from the desert,
and if you have only half a glass of water to offer that person[.] *
* * Someone argued and said * * * I don't think we should give this
person that half a glass of water until it's full * * * I would
venture to say that the person who is thirsty would probably beg you
to give them that half a glass of water, then, go back and fill it *
* * .
We are doing what we can with the knowledge we have rather than
using the argument, which I find actually counterintuitive * * *
that we must have every single thing that we know of in place before
we proceed. [Tr. 7857-7859]
Some of OSHA's expert witnesses who are actively engaged in
research on work-related MSDs testified that an important finding from
the more recent literature is that biomechanical risk factors have been
shown to be associated with MSDs independently from psychosocial
factors (Tr. 1327-1328, 1331-1332, 1335, 1343, 1365, 1412). Dr. Niklas
Krause, in testifying on his own prospective study of public transit
operators and low back disorders (Ex. 500-87-2), stated that
The main result * * * is that both biomechanical and
psychosocial job factors were independently associated with spinal
disorders * * * [I]ndependent positive dose response relationships
were also found for ergonomic problems * * * I conclude from this
new high quality evidence [referring to the Loisel et al.(Ex. 38-28)
randomized trial study] and the literature that has been already
collated by OSHA [in its preamble to the proposed rule and Health
Effects Appendices (Ex. 27-1) that high-quality epidemiological
studies confirm that physical work place factors cause MSDs
independently from individual worker characteristics and
psychosocial job factors * * * [Tr. 1331-1335].
Dr. John Frank testified that the Kerr et al. case-control study (Ex.
38-82) in which he participated also found an association between MSDs
and exposure to biomechanical risk factors independent from
psychosocial factors. When asked about the significance of that
finding, Dr. Frank responded
The importance particularly for the proposed standard or any
public health efforts to reduce biomechanical hazards at work is
that[,] * * * acting on biomechanical risk factors will bring risk
reductions according to our understanding of the multifactorial
causal process even if we are unable * * * at the present time to
conclusively act to reduce psychosocial factors * * * [Tr. 1365-
1366]
Dr. Frank also drew a parallel with successful efforts to control
cholesterol blood levels to reduce heart disease incidence, despite
``two dozen or more'' other risk factors that contribute to heart
disease because high cholesterol levels are independently associated
with an increased risk of heart disease (Tr. 1365-1366).
In the preamble to the proposed rule, OSHA's focus on
identification and control of biomechanical risk factors in the
workplace was based on two considerations. First, OSHA preliminarily
concluded that there was substantial evidence of a clearly demonstrated
causal relationship between exposure to physical risk factors and MSD
outcomes (64 FR 65926), and that most researchers who studied the
etiology of MSDs placed emphasis on biomechanical risk factors. Second,
research into role of psychosocial risk factors in the etiology of MSDs
was considered to be a less mature field than that addressing the role
of biomechanical risk factors, characterized by emerging methodology,
as pointed out by Dr. Martin Cherniak at the hearing (Tr. 1307), and
sometimes by inconsistent results. Thus, most interventions designed to
address work-related MSDs focused on biomechanical, rather than
psychosocial factors.
The 1997 NIOSH review (Ex. 26-1) on which OSHA relied heavily,
examined psychosocial risk factors that might contribute directly and
indirectly to musculoskeletal illness and injury. The review noted that
the results from the literature were not entirely consistent, and that
a lack of consensus on standard measurements and procedures might be
one reason for lack of consistency. Perceptions of intensified
workload, monotonous work, low job control, low job clarity, and low
social support were associated with MSDs in some studies. NIOSH found
that these associations, despite the variance in methods used to assess
these factors, were significant in the better studies; however, the
size of
[[Page 68521]]
effect was relatively weak compared to that of the biomechanical
variables.
In his testimony, Dr. Frank (Tr. 1343-1345, 1397-1398) discussed
the reasons for this inconsistency, relating it to the field being in
the embryonic stage of understanding psychosocial effects, and to
imperfect measurement instruments. He pointed out that the Institute
for Work and Health study discussed below (Kerr et al., 2000, Ex. 38-
82) did not confirm findings of Bigos et al. (1991a, b, Exs. 26-1241,
26-1242, 1992, Ex. 26-1393) or Krause (1998, Ex. 500-87-2) that low job
satisfaction contributed to risk. In contrast, Dr. Frank (Tr. 1344)
noted that, in newer studies that simultaneously assessed the effect of
physical and psychosocial factors, biomechanical loads make a
consistent and generally stronger contribution to MSD outcomes.
Although psychosocial exposure assessment has grown rapidly in the
last decade and is characterized by continually improving
methodological developments, it is still a relatively young field.
Measurement methodologies are not well standardized; this was addressed
by Dr. Barbera Silverstein, who testified that there was no consensus
on the kinds of psychosocial issues that should be studied or how they
could be assessed ``with the same rigor that has been * * * looked at
[for] physical load factors'' (Tr. 17444).
In addition, less is known about the causal relationship between
psychosocial factors and MSDs. Many studies performed so far have been
cross sectional, thus making it difficult to evaluate the temporal
nature of the association (i.e., whether psychosocial factors preceded
the MSD or whether the presence of a disorder led to negative
psychosocial outcomes). Dr. Punnett addressed this issue in her
testimony:
* * * [S]ince psychosocial factors may be perceived and reported
differently by the worker after the development of musculoskeletal
disorders, the reported associations are particularly difficult to
interpret with respect to * * * [etiology].
The occurrence of a work-related musculoskeletal disorder * * *
may itself cause psychosocial strain. And that strain may also
subsequently slow or interfere with the recovery process without
necessarily having been involved in the initial etiology. In this
context, we should note that associations with cross-sectional * * *
[studies] with physical exposures are far less ambiguous. [Tr. 869-
870]
As a result, associations found between psychosocial exposures and
MSD outcomes are, relative to biomechanical associations, less
consistent and generally weaker (NAS, 1999, Ex. 26-37). Further, the
underlying mechanisms are still not nearly as well understood as those
developed for biomechanical associations (Tr. 1344-1345, NAS, 1999, Ex.
26-37). Similarly, understanding and evaluating psychosocial
interventions is also in its infancy, making it difficult to design
appropriate interventions.
None of the studies cited by either proponents or opponents of an
ergonomics standard can demonstrate that any of the risk factors
measured, whether biomechanical, psychosocial, personal, or
demographic, can completely explain an increased prevalence or
incidence of MSD outcomes. (In other words, the combined contribution
of all factors to statistical models never comes close to explaining
100 percent of the variance between exposure groups in the outcome
measure; there are always other, unmeasured factors involved.) Dr.
Tapio Videman (Ex. 32-241-3-20), Dr. Arthur Barsky (Ex. 500-118-1) and
most other researchers agreed that a simple biomechanical model of
tissue wear and tear is not sufficient by itself to explain disease
development in humans, which is characterized by complicated
interactions with external environmental factors and individual
characteristics. In fact, testimony at the hearing (Tr. 868, 1264,
5942-5943) made it clear that considering psychosocial and
biomechanical factors to be separate kinds of exposures is a somewhat
artificial distinction in that the two classes of stressors are
strongly linked, both resulting from core aspects of the organization:
its technology, culture and work organization.
For example, Dr. Punnett testified that
There is also a recognized overlap between some characteristics
of physical and psychosocial work environment.
A repetitive, monotonous job on a machine paced assembly line
can be described equally well by the ergonomist as consisting of
stereotyped repetitive motion patterns with rigid pacing and few
rest breaks or as having poor psychological job content with few
opportunities to make decisions, work collaboratively with co-
workers, utilize existing skills or learn new ones.
And I suggest that the worker performing that job would be hard
pressed to make a distinction between the physical and the
psychosocial characteristics of that job. [Tr. 868-869]
Ms. Sue Rahula, an ergonomist technician with United Auto Workers,
described how biomechanical exposure and the presence of an MSD can
affect worker morale, which can be reflected in negative psychosocial
outcomes:
When you're feeling pain your morale is going to be low, your
discomfort level is low, your attitude is bad, and you may be one of
the silent sufferers. * * * When * * * we take our risk factor
checklist out and we verify that, yes, these postures are awkward
postures and when you add that along with the forces and the
exertions that you're using that that's a possibility it sure could
cause pain. It's no wonder the morale becomes low. And they
[biomechanical and psychosocial factors] do intertwine. But the pain
is usually the cause of [low morale], in my opinion, from what I
see. [Tr. 5942-5943]
These underlying sources of biomechanical and psychosocial exposures
can themselves be seen as a single exposure category known as
organizational exposure (Warren, 1997, Ex. 38-72, Warren et al., 2000a,
b, Exs. 38-75, 38-73, Shannon et al., 1996, 1997, Exs. 26-1368, 26-
1369), which, as Dr. Warren described, recognizes that ``the way work
is organized will have an effect on the levels of both biomechanical
and psychosocial work stresses'' (Tr. 1264).
Summary of Primary Literature on Biomechanical and Psychosocial Factors
OSHA's review of the literature presented below shows that most of
the best studies available suggest that MSDs are the result of a
complicated combination of biomechanical and psychosocial factors, with
the prevalence or incidence of MSDs being generally more strongly
associated with biomechanical risk factors. Given the present state of
research into MSD etiology, there can be little doubt that a
multifactoral model, incorporating both biomechanical and psychosocial
risk factors, would best explain the differences in MSD prevalence or
incidence seen among various groups of workers. Nevertheless, from the
testimony presented above and the review of the literature that
follows, OSHA concludes that biomechanical risk factors contribute
independently from psychosocial factors to MSD etiology, that the
association between the risk of MSDs and exposure to biomechanical risk
factors has been observed to be generally stronger than for
psychosocial factors, and that, consequently, it is reasonable to
design interventions that focus on exposures to biomechanical risk
factors to reduce the risk of MSDs in exposed workers.
Because the scientific literature summarized in this section
addresses the relative strength of association between MSD risk and two
broad categories of workplace factors, and because of the potential for
interacting or modifying effects between biomechanical and psychosocial
factors,
[[Page 68522]]
it becomes particularly important to consider certain elements of
epidemiological study design to ensure that study results are
appropriately interpreted. These design considerations include the
following:
Best study design. Epidemiological studies can be of three general
designs: cross-sectional, case-control, and prospective (longitudinal)
cohort. Dr. Stanley Bigos presented a comprehensive review of the
advantages and disadvantages of each study design (Ex. 32-241-3-4, pps.
7-9). OSHA also addressed general issues regarding study design and
causal inference in a previous part of this Health Effects section. All
researchers agree that prospective studies can most persuasively
establish causality, with cross-sectional studies presenting the most
potential problems in this area. In the absence of any other
information, prospective studies are generally preferable. However,
several factors may recommend against this design: in particular, the
high cost of these studies and the dynamic nature of the modern
workplace, which may change job classifications (and hence workers'
exposures) over the follow-up period of the study.
Although cross-sectional studies identify associations and cannot
by themselves permit a definite attribution of a causal relationship,
it is still possible to draw inferences when one causal direction
(i.e., exposure precedes disease) is much more plausible than the
alternative explanation (i.e., disease precedes exposure). As Dr. Gerr
noted in his testimony (Tr. 1525) the many cross-sectional studies
showing an association between carpal tunnel syndrome and physical
workplace factors strongly indicate that exposure to these workplace
factors causes disease. This conclusion arises in part because it is
illogical to postulate that the presence of CTS would cause exposure to
physical factors (i.e., workers select themselves into physically
harmful jobs on the basis of disease status). Dr Gerr testified that
this would be ``like saying cancer causes smoking. It's as wrong as it
is silly to hear'' (Tr. 1525). However, for psychosocial factors such
as poor job satisfaction or low supervisory support, it is more
difficult to logically infer or exclude a temporal relationship between
a psychosocial factor and an MSD; this was described by Dr. Punnett in
her testimony (Tr. 869). That is, it cannot be known whether having
poor job satisfaction preceded development of the MSD or whether the
presence of the MSD is causing a worker to become less satisfied with
their job. Thus, in evaluating the causal nature of psychosocial
factors, the use of a prospective study design that follows groups of
workers over time becomes particularly important to evaluate the
temporal relationships between exposure to biomechanical risk factors,
psychosocial factors, development of MSDs.
In addition, as was the case with the biomechanical literature
reviewed in earlier parts of the Health Effects section, determination
of exposure and health outcome by objective means, such as direct
observation or measurement of exposure and medical assessment of health
status, is preferable over sole reliance on worker self-reports because
objective measures rule out the possibility of reporting bias (e.g.,
the possibility that a worker's disease status might influence the
self-report of exposure). This design consideration points to another
difficulty in studying the role of psychosocial factors in that they
can only be assessed by administering questionnaires or interviews.
Simultaneous assessment. It is obvious that to accurately assess
the relative contribution of biomechanical and psychosocial risk
factors to MSD causation and exacerbation, both classes of exposure
must be measured.
Address collinearity. Levels of both biomechanical and psychosocial
risk factors are in large part the result of the way work is organized,
the technology and sector of the company, and the organizational
policies and culture that drive work organization. Thus the two classes
of stressor are generally highly correlated in a workplace (Tr. 868-
869, 1264, 5942-5943). Concurrent analysis of exposure-outcome
associations must be very careful to avoid modeling problems that arise
from collinearity.
Assess both stressor categories with equal precision. Some studies
assess both categories of exposure, but assess one with more precision
or detail than the other. The category characterized in more detail
presents fewer opportunities for non-differential exposure
misclassification (which biases results towards a lower effect) and
will thus show artificially elevated relative associations with
outcome. Dr. Wells stated that a factor measured with poor precision in
an epidemiological study will often not appear as a risk factor in
statistical modeling (Tr. 1355).
Ensure adequate variance in all measures. Studies that assess both
categories of exposure, but with little variance between exposure
groups in one or the other category of exposure will generally not find
effects associated with that category or measure. Regression analysis
(a standard modeling method in many studies) cannot assess the
contribution of an exposure if its magnitude or intensity is
essentially the same in all study participants.
Assess both stressor categories at the same individual or group
level. Studies that assess both categories of exposure, but at
different levels of analysis (i.e., the level of the individual worker
versus groups of workers), will generally not find an effect for the
variables measured at a higher (group) level of aggregation; this was
addressed by Dr. Frank in his testimony (Tr. 1364-1365). For example,
the Boeing study (Bigos, et al., 1991a, b, Exs. 26-1241, 26-1242, 1992
Ex. 26-1393) assessed psychological and emotional variables at the
individual level and biomechanical variables at the group level. This
error also reflects violation of the preceding two criteria since
measurement at the group level reduces both precision in the
biomechanical exposure measure (compared to measuring exposure at the
individual level) and variance in biomechanical exposure between
groups. When one variable is aggregated or represented at the group
level, as in the Bigos measurement of biomechanical risk, the
variations in exposure within each group are lost; internal variance
within each group is reduced to zero.
The studies summarized below relied on assessment of both
biomechanical and psychosocial factors in the workplace. Thus, in
accordance with the second criteria described above, studies were
excluded if they did not assess one class of stressor or did not
include both classes in multivariate analysis. Such studies are useless
for the exploration of combined biomechanical and psychosocial effects.
The majority of the studies below demonstrate at least equal, and
often stronger, associations with biomechanical stressors than with
psychosocial. This fact, combined with the independent effects of both
stressor classes, as discussed above, is sufficient to support OSHA's
focus on biomechanical risk factors in the final rule. However,
relative magnitude of the associations for biomechanical and
psychosocial risk factors should only be seen as a qualitative
indicator of relative strength of association with MSD prevalence or
incidence. Actual quantitative effect sizes may not be comparable
within or between studies for a number of reasons, including:
Use of different measurement scales;
Use of different analytical strategies to categorize risk
levels; and
[[Page 68523]]
Use of different outcome measures in different studies.
Table V-14. summarizes the key features of the design of each study
as well as the range of measures of association for biomechanical and
psychosocial factors.
Wickstrom & Pentti 1998 (Ex. 500-121-77). This 2-year prospective
study of 117 white-collar and 189 blue-collar workers in two metal
industry facilities assessed both biomechanical and psychosocial
exposures (4 items each) at baseline, using equivalent levels of
detail. Back pain was assessed twice in the follow-up period by
questionnaire, and data on sick leave attributed to back pain and other
MSDs (doctor diagnosis if over 3 days) was obtained from company
records. The exposure assessment at baseline plus physician diagnosis
at follow-up made this design capable of strongly implying causal
status to both physical and psychosocial risk factors. As predictors of
self-reported LBP, 3 physical exposures were predictive for both white
collar (RRs: 2.82-6.19) and blue-collar workers (RRs: 2.49-3.67). Since
other authors (Marras, 2000, Ex. 500-121-46) have hypothesized that
psychosocial exposures have less effect if the physical load is high,
it is interesting that psychosocial stress was predictive of LBP in
white-collar workers, while none of the 4 psychosocial exposures were
significantly predictive in blue-collar workers. However, sick leave
was predicted for blue-collar workers by both biomechanical exposures
(RRs: 1.72-2.04) and psychosocial (RRs 1.58-1.99). In general, this
study supports the interpretation that MSDs are caused by both classes
of risk factor, with biomechanical showing stronger effects.
Table V-14.--Studies Assessing Both Biomechanical and Physical Risk Factors
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of Results: outcome and
Reference subjects Study type Exposure measure Outcome measure Study design effect
--------------------------------------------------------------------------------------------------------------------------------------------------------
Association with Biomechanical Factors Stronger than with Psychosocial Factors (or effect size not reported)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Wickstrom & Pentti (1998).......... 306 3 1.................. 1, 2, 3............ all LBP & sick leave due to
LBP; Physical RR: 1.97-
6.19; Psychosocial RR:
1.58-1.59.
Bergqvist et al.(1995)............. 260 1 2.................. 3.................. all UE/LBP sympt./MD diag.;
Physical OR: 3.1-7.4;
Psychosocial OR: 2.1-7.4.
Kerr et al.(2000).................. 381 2 3.................. 1.................. all Reporting of LBP; Physical
OR: 1.7-3.0; Psychosocial
OR: 1.6-2.6.
Koehoorn et al.(1999).............. 4020 3 2.................. 2.................. a, c MSD symptoms & claims;
Physical RR: 1.41-4.65;
Psychosocial RR: 0.45-
2.78.
Krause et al.(1998)................ 1449 3 1, 2............... 2.................. b, c Spinal injury through WC;
Physical OR: 3.04
(driving cable car); 0.37
(part-time driving: 20-30
hrs); Psychosocial OR:
1.50-1.56.
Latko et al.(1997, 1999)........... 352 1 2.................. 1, 3............... all Symptoms, MD Dx of CTS;
Physical OR (high
repetition vs. low rep.):
2.32-3.23; Psychosocial
OR: n.s.
Latza et al.(2000)................. 230 3 1.................. 1.................. all Self-reported LBP;
Physical PR: 1.8-4.0;
Psychosocial PR: n.s.
Leclerc et al.(1998)............... 1210 1 1.................. 3.................. all CTS by signs or NCV;
Physical OR: 1.90-2.24;
Psychosocial OR: 1.59-
2.24.
Linton (1990)...................... 22,180 3 1.................. 1.................. all Neck & LBP symptoms
Univariate ORs; Physical:
0.86-2.95; Psychosocial:
1.15-2.60; Combined ORs:
2.42-3.65.
Ono et al.(1998)................... 575 1 1.................. 3.................. all Epicondylitis, MD Dx;
Physical OR: 1.7;
Psychosocial OR: 1.2.
Videman et al.(1989)............... 199 3 2.................. 1.................. b, c Incidence of back injury;
Low skill OR: 37-156 (if
also 3 hrs. strenuous
working postures)
Bernard et al.(1992, 1994)......... 973 1 1, 2............... 1.................. all UE symptoms; Physical OR:
1.4-2.5; Psychosocial OR:
1.4-1.7.
Faucett & Rempell (1994)........... 150 1 2.................. 1.................. all UE symptom severity,
(effect measured by R \2\
change): Physical: 0.11-
0.15; Psychosocial: 0.03-
.12.
Heliovaara (1987).................. * 592 3 1 (occ.)........... 3.................. none Hospital Admission for
disc herniation/sciatica;
Occupational RR: 2.2-3.0;
Psychic Distress: NR.
Josephson & Vangard, 1998.......... 269 2 1.................. 1.................. all LBP medical visit;
Physical OR: 2.3-8.7;
Psychosocial OR: n.s.
Svensson & Andersson (1981)........ 940 ** 1 1.................. 2.................. all LBP sickness absence;
Heavy Lifting (effect
NR); Reduced overtime/
monotonous work (effect
NR).
Thorbjornsson et al.(2000)......... 484 2 1.................. 1.................. all LBP med. visit or absence;
Physical OR: 1.7-2.2;
Psychosocial OR: n.s.;
Interaction OR: 3.1-3.7.
Vingard et al.(2000)............... 2118 3 1.................. 1.................. a, b Care-seeking for LBP;
Physical RR: 1.8-2.9;
Psychosocial RR: 1.5-1.6.
Warren et al.(2000a)............... 845 2 1.................. 1.................. all NIOSH MSD case def.;
Physical OR: 1.89-2.13;
Psychosocial OR: 1.56-
1.69.
Waters et al.(1999)................ 284 1 1, 2............... 1.................. all Prevalence of LBP; Lifting
Index OR: 1.04-2.20;
Satisfaction OR: 4.57-
7.65.
Burt et al.(1990).................. 834 1 1.................. 1.................. all UE Symptoms; Physical OR:
2.0-4.1; Dissatisfaction
OR: 1.9-2.3.
[[Page 68524]]
Lemasters et al.(1998)............. 522 1 1.................. 3.................. c Pain, all body parts, self-
report and MD Dx;
Physical OR: 2.3-3.5;
Psychosocial OR: 1.6-2.9.
Scov et al.(1996).................. 1306 1 1.................. 1.................. all UE and low back symptoms;
Physical OR: 1.64-2.80;
Psychosocial OR: 1.43-
2.04.
Warren et al.(2000b)............... 7712 1 1.................. 1.................. all MSD symptoms & pain;
Physical : 0.06-
0.16; Psychosocial : 0.04-0.12.
Hales et al.(1992, 1994)........... 533 1 1.................. 1.................. a, b UE MSD symptoms; Physical
OR: 1.1-3.8; Psychosocial
OR: 1.1-3.5.
Hoekstra et al.(1994).............. 108 1 1.................. 1.................. a, b MSD symptoms; Physical OR:
3.5-5.1; High Control: OR
0.6.
Houtman et al.(1994)............... 5865 1 1.................. 1.................. b, c Complaints: muscle/joint &
back; chronic back
problems; Physical OR:
1.36-1.62; Psychosocial
OR: 1.20-1.35.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Association with Psychosocial Factors Stronger than with Biomechanical
--------------------------------------------------------------------------------------------------------------------------------------------------------
Viikari-Juntura & Riihimaki (2000). 5179 3 1.................. 1.................. all Radiating neck pain;
Physical OR: 1.2-2.3;
Psychosocial OR: 1.1-6.1.
Waters et al.(1999)................ 284 1 1, 2............... 1.................. all Prevalence of LBP; Lifting
Index OR: 1.04-2.20;
Satisfaction OR: 4.57-
7.65.
Elberg et al.(1995)................ 637 1 1.................. 1.................. all Neck & shoulder symptoms;
Physical OR: 1.2;
Psychosocial OR: 1.2-1.3.
Sauter (1984)...................... 333 1 1.................. 1.................. all Somatic complaints;
Physical : 0.16-
0.21; Psychosocial : 0.19-0.26.
Warren et al.(submitted)........... 7712 1 1.................. 1.................. all LBP, absenteeism; Physical
OR: 1.45-1.88;
Psychosocial OR: 1.32-
2.27.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Biomechanical Effect Not Significant
--------------------------------------------------------------------------------------------------------------------------------------------------------
Leino & Hanninen (1995)............ 902 3 1.................. 1, 3............... b, c Back/limb symp. & MD Dx;
Physical : n.s.;
Psychosocial :
.110-.146.
Bigos et al.(1991a)................ 3020 3 1, 2............... 2.................. none Reporting back injury;
Physical RR: n.s.;
Psychosocial RR: 1.34-
1.70.
Svensson & Andersson (1989)........ 1746 1 1.................. 1.................. all Low back pain; Physical
n.s.; effect NR; Fatigue,
dissatisfaction, worry;
sig., but effect NR.
--------------------------------------------------------------------------------------------------------------------------------------------------------
n.s.: not significant
NR: controlled for factor, but effect not reported
Table only notes statistically significant effects (p0.05)
Key:
Study Type:
1--Cross sectional
2--Case-control/Referent
3--Cohort/Prospective
Exposure Measure:
1--Worker self-report
2--Observation of job
3--Instrumentation
Outcome Measure:
1--Worker self-report
2--Observation/record
3--Clinical findings
Study Design
a--Biomechanical and psychosocial factors studies with equal precision
b--Biomechanical and psychosocial factors assessed at same individual or group level
c--Adequate variance between groups in all measures
* case 2140 con.
** retro. outcome
Bergqvist, Wolgast, Nilsson, Voss 1995 (Ex. 26-1195). hese
investigators found a number of upper extremity diagnoses to be
consistently associated with standard biomechanical risk factors
(especially postural stressors, ORs 2.2-4.4, and lack of rest breaks,
ORs 2.7-7.4); some personal factors (especially age and presence of
children at home), task flexibility (OR 3.2) and quality of peer
contacts (ORs 2.1-4.5) had independent associations. Although the study
was cross-sectional, confidence in study findings is improved by the
detailed physical examination used to determine outcome and the broad
array of exposure measures (including individual factors, non-work
risks, work organizational factors and biomechanical factors). Muscle
problems in each body location showed a different pattern of personal,
psychosocial and biomechanical stressor associations.
Faucett and Rempel 1994 (Ex. 38-67). his study of 150 newspaper
editorial work found that upper extremity pain and numbness symptoms in
VDT workers were related primarily to postural variables (R2
changes 0.11-
[[Page 68525]]
0.15), with smaller additions to model R2s from
psychological demands, decision latitude, and employee relationship
with the supervisor (R2 changes 0.03-0.12). The effects of
postural variables on upper torso pain and stiffness were greater than
those for pain and numbness (R2 changes 0.19-0.32), while
psychosocial effects were reduced (R2 changes 0.01-0.08).
Interaction terms between keyboard height and psychosocial variables
added to the model R2s (R2 changes 0.04-0.15),
suggesting that the effect of biomechanical variables can be modified
by psychosocial variables. In this study, biomechanical stressors were
clearly the dominant factor, but the size of the effect for interaction
terms may have meaning for the mechanism of psychosocial action as
being an effect modifier.
NIOSH Health Hazard Evaluations (Exs. 26-439, 26-842, 26-725).
Three cross-sectional NIOSH studies, at the L.A. Times (Bernard,
Sauter, Petersen, Fine, & Hales, 1992, Ex. 500-165-20, 1994, Ex. 26-
439), Newsday (Burt, et al., 1990, Ex. 26-842) and two Social Security
Administration teleservice centers (Hoekstra et al., 1994, Ex. 26-725)
found associations of biomechanical risk factors (in particular,
duration of VDU work) with MSD symptoms, while also finding independent
associations of these symptoms with several psychosocial factors.
Another NIOSH HHE at U.S. West Communications (Hales et al. 1992 (Ex.
26-727), 1994 (Ex. 26-131) did not find associations between symptoms
and physical workplace characteristics other than use of bifocal
glasses (OR 3.8), because the standardized workstations presented
virtually no variance in biomechanical measures. Thus, psychosocial
factors were dominant in the models, although work pressure (OR 1.1-
1.2), workload surges (OR 1.2) and information processing demands (OR
1.2) probably represent a combination of physical and psychosocial
exposures. See Table V-14. for strength of association estimated by
multivariate logistic regression models in all these studies.
Kerr, et al.2000 (Ex. 38-82). Researchers at the Institute of Work
and Health (IWH) have carried out several well-designed studies
measuring both biomechanical and psychosocial stressor levels in
detail. These studies demonstrate the independent contributions of
biomechanical, psychosocial and organizational factors to models
explaining back injury and accidents (Shannon et al., 1996, 1997, Exs.
26-1368, 26-1369). The most recent IWH study (Kerr, et al., 2000, Ex.
38-82), performed in concert with the Ontario Universities Back Pain
Study (OUBPS) group, is a case-control study reviewed in detail by John
Frank (Ex. 37-27). Subjects reported levels of physical demands
(including perceived exertion) as well as psychosocial factors. In
addition, videotape analysis and biomechanical modeling provided
quantifiable estimates of actual spinal loading. These biomechanical
measures acted independently to substantially increase risk of workers
reporting new cases of LBP, after controlling for individual and
psychosocial factors. In final models, the biomechanical risk factors
demonstrated ORs of 1.7-3.0, while psychosocial risks were associated
with ORs of 1.6-2.6. This study improved on earlier study designs by
directly measuring forces on back during job performance. The case-
control study also matched controls by actual job, allowing analysis of
the degree to which job exposures influenced self-reported LBP.
Compression, peak shear force, peak hand force were associated with
doubled risk of LBP reporting. These findings are consistent with much
of the other epidemiological data reviewed in this section. Thus this
study strengthens confidence in the results of other studies that rely
on less detailed exposure assessment and/or self-reported exposures and
outcomes.
Krause et al.1997 (Ex. 38-267), 1997 (Ex. 38-266), 1998 (Ex. 500-
87-2). Niklas Krause and colleagues, studying a cohort of San Francisco
drivers, examined relationships between biomechanical and psychosocial
exposures and neck and shoulder outcomes. The cross-sectional analyses
(Krause et al., 1997a, Ex. 38-267, 1997b Ex. 38-266) determined that
both biomechanical and psychosocial job factors were separately and
simultaneously associated with non-disabling neck and back pain. The 5-
year longitudinal follow-up of this cohort (Krause et al., 1998, Ex.
500-87-2) found that workers' compensation cases of spinal injury were
predicted by a combination of biomechanical (measured by hours driving)
and psychosocial risk factors at baseline. (See Krause testimony, Ex.
37-15). The physical risk factors addressed by this measure of hours
spent driving included prolonged sitting, twisting/bending, vibration,
and use of foot pedal (Krause testimony, Tr. 1376, Ex. 37-15). Although
all measures were gathered at the same (individual) level, the
surrogate measure for biomechanical exposure (hours spent driving) was
a more generalized measure than the psychosocial data and thus subject
to greater non-differential misclassification and consequent dilution
of effect in statistical modeling. Psychosocial stressors demonstrated,
on average, higher ORs than the surrogate physical measure of hours
spent driving. This is an example of the fourth study design criterion
discussed above: the factor measured in greater detail has a greater
likelihood of showing stronger associations in the modeling. The fact
that a biomechanical effect still emerged in the modeling strongly
suggests that if physical exposures were measured in the same detail as
psychosocial exposures, they would have demonstrated a larger effect in
modeling; however, it cannot be known whether the resulting size of the
effect for biomechanical factors would have surpassed that for
psychosocial factors. For cable car operators, biomechanical factors
were more strongly associated with back cases than were psychosocial
factors.
In his written comments, Dr. Nortin Hadler (Ex. 32-241-3-8)
demonstrated a basic misunderstanding of the research by taking the
Krause studies to task for showing a biomechanical effect only for
cable car drivers. The data did show that only cable car drivers'
injury rate was significantly elevated when compared to diesel bus
drivers. However, the pooled data for all drivers showed a highly
significant increase (2.7 times) in injury rate between drivers who
worked 20-30 hrs per week compared to those who worked 31-40,
suggesting a significant effect related to biomechanical factors.
Hours-per-week-driven was the study's surrogate measure for exposure to
physical risk factors.
Latko et al.1997 (Ex. 38-122), 1999 (Ex. 38-123). These researchers
performed a cross-sectional study with some of the most detailed
exposure assessments to be found in the literature. The study,
described elsewhere in the testimony (Franzblau, Ex. 37-3, Armstrong,
Ex. 37-21) measured a wide variety of demographic, personal, and
exposure variables, including 13 psychosocial parameters. It is
distinguished by precise measurement of exposure variables and several
levels of outcome measurement objectivity, ranging from symptom
reports, through physical findings, to nerve conduction velocity (NCV)
results. The contribution of the psychosocial variables did not reach
significance in the final modeling, strongly implying that the effect
of biomechanical factors predominates in these 3 manufacturing plants
(testimony
[[Page 68526]]
by Armstrong, Ex. 37-3, Franzblau, Ex. 37-21).
Nortin Hadler (post hearing comments, Ex. 500-118-1, p 7) cited
this study as evidence for a lack of a significant association between
repetitive motion and decrements in median NCV. These results were, in
fact, marginally significant. Moreover, if a more conservative
definition of CTS was used, (i.e., 0.8ms threshold plus positive hand
diagram report), the association was significant (Franzblau testimony,
Ex. 37-21). In addition, Dr. Hadler failed to note either the wide
range of significant associations found for repetition, symptom reports
and tendinitis as indicated by physical exam findings, and that these
associations did demonstrate a positive exposure-response relationship.
Warren 1997 (Ex. 38-72), Warren et al.2000 (Ex. 38-73). Nicholas
Warren and colleagues at the University of Massachusettes at Lowell and
at TNO, the Netherlands, performed analyses on the Dutch Monitor data
set, collected from a broad sample of companies and industry sectors in
1993--a cross-sectional study. The data set contained completed
questionnaires from 7,717 Workers in 528 companies that assessed in
detail both workplace exposure to biomechanical and psychosocial risk
factors and a variety of musculoskeletal and stress outcomes, as well
as reports of extended sick leave. Controlling for gender, education
and tenure on the job, the multivariate linear analyses found roughly
equal contributions of both stressor classes to the pain and MSD
symptom reports, with physical factors having a somewhat larger
magnitude of effect (standardized regression coefficients of 0.06-0.16)
than psychosocial (0.04-0.12). Logistic modeling of low back pain and
absenteeism outcomes found similar results, with biomechanical ORs of
1.35-1.88 and psychosocial ORs of 1.32-1.64, excluding social support.
However, low social support did demonstrate the highest OR (2.27) in
the model explaining low back pain. The study was cross-sectional and
thus could not definitively evaluate temporal associations. However its
large size and wide range of companies and sectors allowed precise
separation of biomechanical and psychosocial exposure-outcome
associations, without collinearity problems.
Dr. Alf Nachemson criticized this study (post-hearing comments, Ex.
500-118-1), confusing it with a completely different study of a
different database submitted to Spine. The results of this study are
reported in a doctoral thesis (Warren, 1997, Ex. 38-72) and an article
submitted to the Scandinavian Journal of Work Environment and Health
(Warren et al., 2000b, 38-73). Contrary to Dr. Nachemson's
mischaracterization, the express purpose of this study was to
simultaneously measure biomechanical and psychosocial MSD risk factors
at the same level and degree of detail.
Warren et al.2000 (Ex. 38-75). Warren and colleagues from the
University of Connecticut Health Center carried out a separate study of
the Connecticut working population, using a random-digit-dialing study
design. This cross-sectional study is one of the few to randomly sample
workers with unreported cases of MSD (using the NHIS definition; Tanaka
et al.1995 (Ex. 26-59)). Psychosocial and biomechanical variables were
assessed at equal levels of detail. Logistic regression analysis found
case status to be associated with a broad mix of psychosocial and
biomechanical stressors, with biomechanical exposures showing somewhat
higher odds ratios. Significant psychosocial ORs ranged from 1.56-1.69,
while biomechanical ORs were between 1.89 and 2.13. Stressors were
measured at equivalent levels of detail and demonstrated independent
effects for psychosocial and biomechanical exposures.
Koehoorn, 1999 (Ex. 500-40). This doctoral thesis used a
retrospective cohort design to follow 4020 health care workers from an
acute-care hospital over a 4-year follow-up period, assessing outcomes
of musculoskeletal symptoms and claims. Results varied by body
location. In multivariate models explaining upper body symptoms, a
biomechanical index showed risk ratios of 1.41-1.84, while psychosocial
variables showed RRs ranging from 0.45-2.78. For lower-body symptoms,
RRs for biomechanical risk factors ranged from 2.12-4.65; psychosocial
variables generally did not reach statistical significance. Outcomes of
compensation claims related to these two body areas showed similar
ranges of effect. In subcohorts analyzed for departmental sicktime and
overtime, increased sick time was associated with symptoms and claims,
but increased overtime was not. The study design assessed detailed
biomechanical factors by observation, but only by occupational title,
while psychosocial factors were assessed by individual questionnaire.
Thus, the relative strength of association may have been underestimated
for biomechanical stressors. This large, carefully designed cohort
study provides evidence for a multifactoral model of MSD causation,
with physical factors being more strongly associated with MSD
incidence.
Waters et al.1999 (Ex. 500-41-54). This study was designed to
provide epidemiologic data linking the NIOSH lifting index (LI, a
quantitative measure of manual lifting stress calculated with the
revised NIOSH lifting equation) to prevalence of low back pain.
Measurements used to calculate the LI were collected on a sample of
workers over a 2-4 day period by trained observers. Workers also
completed a self-administered questionnaire that included psychosocial
items. In multivariate modeling, increasing values of the LI were
associated with increases in period prevalence of LBP over the last 12
months, with an exposure-response relationship that reversed at the
highest LI (>3). The authors noted that this drop in negative outcomes
in the highest exposure category is seen in other studies and seems to
indicate a ``healthy worker'' or survivor effect (representing the
departure of workers with pain or high risk of back injury from highly
stressful jobs). Psychosocial factors of demands, control and social
support did not enter significantly into these models, perhaps because
they were entered as continuous, not categorized, variables. However, a
four-category measure of decreasing work satisfaction showed a
significant exposure-response relationship with LBP. This high-quality
study, which relied on independent measurement of physical job
characteristics, demonstrated the combined contribution of physical and
some psychosocial stressors to prevalence of LBP, with physical effects
predominating in multivariate modeling.
Leclerc et al. 1998 (Ex. 500-41-85). This cross-sectional study of
1210 workers in 3 industry sectors incorporated a sophisticated mixture
of individual measurement of both physical and psychosocial factors,
combined with group-level assessment of cycle time and autonomy. Given
the study design principles outlined above, the effects of these group-
level factors may thus be underestimated. With this caveat, the
research still demonstrated a combined contribution to physician-
diagnosed CTS for cycle times less than 10 seconds (OR 1.90) and
psychological ``problems'' (OR 1.41). Other physical and psychosocial
factors dropped out of this model. In a final model incorporating the
presence of just-in-time production organization at the plant, this
factor replaced cycle time, with an OR of 2.24. Other physical and
psychosocial risk factors were associated with marginal significance.
[[Page 68527]]
The work organization variable of just-in-time production is probably a
surrogate for a combination of increased biomechanical and psychosocial
risk. This study thus demonstrates the combined contribution of both
types of risk. This study also found that industry sector did not enter
significantly into the model when both physical and psychosocial risk
factors were more precisely measured at the individual level.
Latza et al.2000 (Ex. 38-424). This prospective study of
construction workers in Hamburg took detailed observational
measurements of biomechanical stressors associated with a wide variety
of construction tasks. Of the 571 workers who filled out baseline
questionnaires, 285 individuals free of LBP were selected; 230 were
followed up after 3 years. The physical stressors at baseline predicted
subsequent 1-year prevalence of LBP (PRs: 1.8-4.0), while psychosocial
stressors did not enter significantly into the models. This is somewhat
surprising since, although the physical stressors were evaluated in
detail, they were measured at the job level, while psychosocial factors
were measured at the individual level. As noted above, this usually
results in an underestimate of the physical stressor contribution
relative to psychosocial factors.
Vingard et al.2000, MUSIC study (Ex. 500-41-51). The Swedish MUSIC
project has consistently demonstrated combined associations of
biomechanical and psychosocial stressors with back, neck and shoulder,
and other disorders. This study assessed prospectively the individual
and combined effects of physical and psychosocial exposures on
subjects' seeking care for LBP over a 5-year period. Gender
stratification reduced significance levels but demonstrated somewhat
different exposure-outcome associations for males and females. For men,
forward bending and manual material handling time, when compared to
levels 5 and 10 years ago, were significantly predictive (RR 1.8 and
2.0 respectively) with a combined exposure having a RR of 2.8. This
combined exposure was also significant for females (RR of 2.3). For
both genders, a combination of physical stressors including metabolic
stress was also a risk factor. Although included in these multivariate
models, most psychosocial stressors did not enter significantly
(exceptions were low work satisfaction and low skill use for males, RRs
of 1.6 and 1.5, respectively). A subset of the study sample reflecting
a combination of high physical load and high psychosocial load showed
much higher RRs, but the sample size was small. Overall, the MUSIC
study provides well-designed and detailed evidence that physical and
psychosocial exposure combine in the etiology of LBP, with the physical
stressors demonstrating stronger effects.
Houtman et al.1994 (Ex. 26-1230). This paper reported a cross-
sectional analysis of pooled 1977-1986 results from the National Work
and Living Condition Survey in the Netherlands. The study asked one
question on work pace, four on intellectual discretion, and one on
physical load. The items were all assessed at the same level of
precision (dichotomous, yes/no) and at the same analytical level, but
the greater detail in intellectual discretion assessment may have
biased the estimated effects of that particular construct upwards.
Multivariate logistic regression models were constructed to explain
variance in 3 musculoskeletal outcomes: back complaints, muscle/joint
complaints, and chronic back problems. Work pace was consistently
associated with these outcomes (ORs 1.21-1.29) as was heavy physical
load (ORs 1.36-1.62). Of the intellectual discretion items, only one,
monotonous work, was consistently associated with musculoskeletal
symptoms (ORs 1.29-1.35), but when all four items were combined, the
scale demonstrated the strongest association of the study with chronic
back pain (OR 2.10). Thus, in addition to providing more evidence for
independent association of physical and psychosocial stressors with
musculoskeletal outcomes, the study supports the hypothesis that
psychosocial stressors have their strongest effect with duration of
pain, not its inception.
Videman et al.1989 (Ex. 26-1155). This study is difficult to
interpret, but is included because of its relevance to interventions.
The researchers dichotomized graduating nursing students by skill
level. Half the students had received traditional lifting training;
half had received advanced, biomechanically-oriented training. Skill
assessment was performed through video analysis of standardized tasks,
not by simple assignment to trained or untrained groups. Nurses were
also dichotomized by hours/day in strenuous postures (3 hrs/day, >=3
hrs/day). In addition, the study collected extensive anthropometric,
strength and psychological measures. Incidence of back injury was
assessed at a 1-year follow-up. The results seem to confuse training
level and activity level, but a combination of >3 hours/day of
strenuous activity and low skill level significantly predicted self-
reported incidence of back injury (ORs of 37 or 156, further stratified
by high and low abdominal strength, respectively). The authors
emphasized that ergonomic interventions must be coupled with training
and describe the training as resulting in biomechanically less
stressful lifting choices by nurses. They concluded that training is an
effective intervention and ``the biomechanical and ergonomic components
of training in patient-handling appear to be inescapable'' (Ex. 26-
1155).
Thorbjornsson et al. 2000 (Ex. 500-71-49). This retrospective
nested case control study examined a cohort of 484 subjects from the
general population, examined first in 1969 and again, 24 years later,
in 1993. Exposure information was collected retrospectively for the 24-
year period and the 12 months previous to the 1993 interview. Outcomes
measured were LBP that resulted either in a medical visit or sick leave
more than 7 days. The study identified a small number of physical
factors (heavy physical work, sedentary work) and psychosocial factors
(poor social relations and overtime work) associated with LBP, as well
as high load outside of work. Most importantly, the research
demonstrated significant ORs for a wide variety of interaction terms
between workplace biomechanical and psychosocial risk factors (ORs:
2.2-3.5). In final modeling incorporating the interaction terms,
individual psychosocial effects became non-significant, but an
interaction between poor social relations and overtime work showed an
OR of 3.1-3.7 for men, depending on LBP onset time. The finding of
significant interactions between biomechanical and psychosocial factors
suggests that control of biomechanical risk factors in the workplace
should reduce not only the effects associated with biomechanical risk
factors, but the effects of their interaction with psychosocial
exposures.
Boeing Study. (Bigos et al.1991 (Ex. 26-1241), 1991 (Ex. 26-1242), 1992
(Ex. 26-1393)).
These studies were discussed earlier in the Health Effects section. In
addition, several witnesses who appeared at the public hearings (Frank,
Krause, others, e.g. Exs. 37-27, 37-15) have explored the
methodological problems with this study, which explain its finding that
the only significant predictor of back pain reporting found was job
dissatisfaction. In sum, the study assessed physical factors at the
group level (although the articles never make clear the exact
methodology), while assessing psychosocial and psychological variables
at the individual level. Assessed at the group level, the variance
[[Page 68528]]
in predictive physical factors was drastically reduced. For instance,
Dr. Bigos stated (Bigos et al., 1991b, Ex. 26-1242, testimony, Tr.
6908) that no-one was required to lift over 20 lbs., and no-one
actually lifted more than 50. However, the analysis had no way to
assign actual lifting frequency or compressive forces at the individual
level. It is difficult to determine whether even the poor
characterization of physical load approached statistical significance
because the authors elected simply not to report results that were not
significantly associated with outcomes (testimony, Tr. 6786). In
addition to this measurement problem, psychosocial and psychological
factors were measured with much greater precision. As noted above,
these assessment differences virtually ensure the primacy of the
better-measured factors, in this case the psychosocial factors, in
statistical modeling.
In addition, the factors entered in the Boeing study models
explained only an extremely small percentage of variance in the
outcome; job satisfaction explained 2.2 percent and psychological
variables explained 1.9 percent. All of the psychological, physical
exam and medical history variables assessed in the study combine to
explain only 8.6 percent of the variance (Bigos et al., 1992, Ex. 26-
1393). Thus, 91.4 percent of the variance in reporting of back pain is
not explained by the combination of poorly measured physical risk
factors and the more detailed psycho-emotional factors. This suggests
relatively poor characterization of overall exposure.
The flaws noted above also pertain to the psychological factor
assessment in this study. Psychological factors were measured at a much
finer level of detail than physical factors, which were measured at the
group level. Overall explanatory power of any of these measures was
poor. As a minor point, specific to the psychological assessment, the
study used non-standard and out-of-date instruments (Cherniack
testimony, Tr. 1150).
Svensson and Andersson 1989 (Ex. 26-732). This study evaluated the
association of a number of physical and psychosocial and psychological
variables with incidence (retrospective) and prevalence of LBP in
women. Both physical and psychosocial/psychological variables showed
univariate associations with the outcome, but multivariate analysis
found associations only with 3 ``psychological'' variables:
dissatisfaction with the work environment, worry/tension at the end of
the day, and fatigue. The analysis is not helpful to the separation of
physical and psychosocial effects for three reasons. First, the study
only reports the p-value range of the significant associations and does
not report effect size, thus making it impossible to tell if physical
exposures were of near significance and to compare relative strength of
association. Second, it is not at all clear whether variables of
dissatisfaction and worry/tension represent a psychological exposure or
an outcome, resulting from an underlying combination of physical and
psychosocial/psychological workplace factors, or from underlying
symptoms (see, Linton, 2000, Ex. 26-642). Most importantly, it is
clearly a mistake to label ``fatigue'' a psychosocial variable. In
fact, fatigue represents an integrated measure of all stressors,
physical and psychosocial, encountered by the worker and may well be
weighted towards the obvious biomechanical stressors. As such, it is
not surprising that this measure might capture variance from the
individual physical exposures tested in the study. (Recall how the
combined index of psychosocial exposures in the Houtman et al.study,
(1994, Ex. 26-1230) had the highest ORs in the study, while the
individual items composing the index had much lower ORs.) As
confirmation, it is interesting to note that these authors' earlier
research (1983, Ex. 26-1158), which assessed a similar set of exposures
but did not include the fatigue item, did demonstrate a contribution
from a physical stressor (high degree of lifting). Thus, this research
appears to be unable to accurately separate the contribution of
physical and psychosocial/psychological factors to LBP.
Leino and Hanninen 1995 (Ex. 38-76). This paper reported the
results of a prospective study begun in 1973, in 2653 industrial
workers, including managerial and office positions. Nine hundred two of
these participants were reexamined after 10 years. Outcomes were self-
reported musculoskeletal symptoms and evaluations by physiotherapists.
At follow-up, both self-reported symptoms and medical findings were
predicted by one psychosocial scale (social relations, OR 2.63-3.41)
and occupational class (OR 2.67-3.73). The only factor that partly
captures physical load in this model is occupational class. A single,
4-level measure of physical load was also entered into the equation.
However, this measure is much less precise than the 6-question scale
(each item with 5 levels) assessing social relations. This unequal
precision would bias the results towards the exposures measured with
greater precision, the psychosocial factors.
The authors noted that their physical load measure did enter into
the cross-sectional models at baseline, along with more psychosocial
exposures (work content, overstrain) and occupation. It was surprising
to find that physical load (a slightly more precise measure of
biomechanical exposures than exposure) dropped out of final models
while occupation class remained. Both physical load and occupation in
this study represent biomechanical exposures assessed at a much less
precise level than the psychosocial measures. This study, though
provocative, cannot provide useful information about the relative
strength of effect.
Summary of Literature Reviews
Several reviews have been published that have evaluated the
literature dealing with work-related MSDs; many of these reviews
included evaluations of studies that concurrently examined the effects
from exposure to both biomechanical risk factors and psychosocial risk
factors. In this section, OSHA summarizes the reviews contained in the
rulemaking docket.
Burdorf & Sorock 1997 (Ex. 502-232). These authors reviewed 35
studies that collected quantitative information on exposures and back
disorder outcomes. Eight of these studies assessed psychosocial and
biomechanical risk factors simultaneously. Of these, six found positive
associations of back disorders with a combination of physical and
psychosocial exposures and two identified several of the physical
factors to be significantly associated, while the psychosocial factor
measured (job dissatisfaction) did not show a significant association.
The analysis identified lifting or carrying loads, whole-body
vibration, and frequent bending and twisting to be the biomechanical
risk factors having consistent associations with work-related back
disorders. Unlike some other studies (e.g., Leino & Hanninen, 1995, Ex
38-76), height and weight (as well as gender, exercise and marital
status) were consistently not associated with back disorders in these
studies. The review identified low job decision latitude and job
dissatisfaction as possibly important predictors of MSDs, but the
evidence was not consistent across studies with different designs.
Although the majority of these eight studies acknowledged the
importance of psychosocial factors, the generalization that emerges
from them is that biomechanical factors were more
[[Page 68529]]
consistently associated with back disorders.
Punnett and Bergqvist 1997 (Ex. 38-13). This review of a large
international body of literature linking biomechanical and psychosocial
factors to upper extremity symptoms and findings in computer users
(classified by neck/shoulder, arm/elbow, and hand/wrist). The authors
found strong, consistent evidence linking MSD development with
biomechanical factors (hours/day and cumulative years of exposure,
intensive or repetitive data entry, and non-neutral postures due to
poor workstation design), while controlling for work organizational and
psychosocial factors in 7 of the 72 papers included in the analysis.
The work organizational factors included in 3 papers (repetitive work,
work pressure and insufficient rest breaks represent a combination of
physical and psychosocial risks. In 4 papers, this review found
suggestive but inconsistent associations (making generalization
impossible) between MSD symptoms and the psychosocial factors of low
decision latitude, low social support, job insecurity and job
dissatisfaction (Bergqvist et al., 1995, Ex. 26-1195, Faucett &
Rempell, 1994, Ex. 38-67, Kamwendo et al., 1991, Ex. 26-1384, Hoekstra
et al., 1994, Ex. 26-725). The authors also noted the difficulty of
using job dissatisfaction as a predictor for MSDs since it could easily
be either a cause or consequence of an MSD.
Lagerstrom et al. 1998 (Ex. 38-102). In this review of studies
relating to low back problems in nursing, 42 articles passed the
inclusion criteria: 21 cross-sectional, 10 prospective, and 11
intervention (also prospective). One of the reviewers' quality criteria
was that the studies include both physical and psychosocial exposure
information. The authors noted that a problem in many of the studies
was the assessment of physical stressor information at an aggregate or
group level, while psychosocial exposures were assessed at the
individual level. As noted above, this non-comparability would tend to
underestimate biomechanical effect in relationship to psychosocial
effect. Still, the authors conclude from their review that
biomechanical and psychosocial exposures generally combine in their
associations with or (in prospective studies) effects on back disorder
outcomes. Looking at well-designed studies with dual exposure
measurement, the authors report that ``[t]o our knowledge there are no
studies that show that work organizational or psychosocial factors, as
such, cause low-back problems.'' They do acknowledge the importance of
these factors in the ``consequence and maintenance'' of low-back
related disorders, through differences in pain perception and reporting
behavior.
Bongers et al. 1993 (Ex. 26-1292). This article was one of the
earliest reviews of the evidence for an association between
psychosocial factors and MSD outcomes. The authors looked at 29 cross-
sectional and 3 longitudinal studies addressing work-related
psychosocial factors. Of these, 22 measured physical load, and the
authors of this review did not think that the physical load assessment
was of a high enough quality to specifically assign relative
association effects to physical and psychosocial factors. Thus, this
review is included to demonstrate how far the field has moved since
1993. Subsequent reviews and studies addressed in this section show
that research in the intervening 7 years has moved towards more
accurate characterization of biomechanical and psychosocial loads and
defining their associations with MSD outcomes.
National Academy of Sciences, 1999 (Ex. 26-37). The NAS study
(cited by Armstrong, Exs. 37-21, 37-1, 37-9 and others, Ex. 37-15,
testimony) was discussed in OSHA's preamble to the proposed rule and is
described in part B of this Health Effects section. It reviewed a
number of studies that found strong evidence for biomechanical
contribution to MSD etiology, controlling for psychosocial factors.
Linton, 2000 (Ex. 26-642). This paper is a careful literature
review of studies addressing the association between psychological
factors and back and neck pain. The author concentrated on individual
psychological measures (i.e., internal psychological factors) but also
included some external psychosocial factors. Since many of the studies
also assessed outcomes of disability and time to return-to-work (RTW),
the author was able to provide evidence for his suggestion that
psychological factors may play a greater role in these long-term
outcomes.
The findings of this review are strengthened by its assessment of
only prospective studies. This might allow an interpretation that the
positive relationship found between various psychological factors and
the outcomes of pain, disability, RTW time, etc. might represent a
causal connection. However, there are two important caveats. Dr. Linton
noted that longitudinal relationships of this sort may still mask
reverse causal connections. The studies generally cannot determine
whether some psychological ``predictor'' variables and the outcome
variables are not both the result of initial or underlying pain.
Secondly, he noted that the psychological variables identified in the
37 reviewed studies explain only part of the variance in outcome. Thus,
the review's results are consistent with the multifactoral model of MSD
etiology (including biomechanical, psychosocial, psychological and
personal variables).
Despite the care with which the studies were selected and analyzed,
however, the review did not identify the type of biomechanical
exposures assessed in the studies or the level at which they were
studied. Instead, it simply noted that 18 studies controlled for
miscellaneous confounding factors, one of which was ``workplace
factors''. No indication was given as to the nature of these factors
and which of these 18 studies addressed ``workplace factors''. Given
the age of some of the papers, controlling for other factors (instead
of simultaneously assessing their effect) is understandable, but it
renders the review useless in contributing to the central debate
concerning relative contribution of biomechanical and psychosocial
factors (i.e., both external psychological and social workplace factors
and internal psychological factors). To further compromise the utility
of this review, the studies evaluated in this review included several
that measured physical exposure at the wrong analytical level (e.g.,
Bigos et al., 1991, Exs. 26-1241, 26-1242) or at a reduced level of
detail (e.g., Leino & Hanninen, 1995, Ex. 38-76, Viikari-Juntura et
al., 1991, Ex. 26-1219), compared to the psychological factors. This
review, although a significant contribution to the literature overall,
provides no useful information concerning relative contribution of
physical and psychological factors to MSDs.
Nachemson 1999 (Ex. 32-241-3-31). This article is a comprehensive
review of the studies purporting to demonstrate that physical workplace
factors are irrelevant to the development of back pain, injury and
disability. Instead, the studies implicate personal biology and
psychological factors, stress and psychosocial factors in the
workplace, and the monetary incentives of the compensation system. Some
of these studies have been addressed above (e.g., Bigos, 1991b, Ex. 26-
1242). In general, Dr. Nachemson's claim that these factors contribute
to low back disorders is credible. Very few of the researchers cited
above would deny their contribution. What is emphatically not credible
is the claim that physical factors are thus not implicated.
[[Page 68530]]
There are 3 primary problems with this claim. First, many of the
studies cited in the article have not assessed the role of physical
factors at all or have assessed them at levels of analysis or detail
that make examination of their contribution impossible. The results of
these errors have been discussed above. These studies overestimate the
role of non-physical risks and thus cannot address the question or
relative effects of biomechanical and psychosocial exposures in the
workplace.
Second, the basic conceptual gap in the Nachemson review is a
failure to acknowledge and address the implications and mechanism of
multifactoral causation. There is a broad literature of well-designed
studies, both epidemiological and laboratory (reviewed above and in
earlier parts of the Health Effects section) demonstrating that
psychosocial and psychological factors can add to the effects of
physical exposures or even potentiate them (interaction or effect
modification) (see Linton, 1990, Ex. 26-977, for a clear example). Dr.
Nachemson's reluctance to consider such effects is represented by his
citation of the Valfors et al. (1985, Ex. 26-685) examination of LBP.
This study reported that physical risk factors (poorly characterized by
a physiotherapist and a physician) were similar in workplaces of
controls and low back cases, while reporting case/control differences
in psychosocial work environment (again, poorly characterized). Valfors
thus attributed the back injuries in the case group to the psychosocial
factors. The logical fallacy, of course, is to assume that this
difference removes physical exposures from a causal role. The more
logical explanation, especially in light of all the evidence for
multifactoral etiology presented in this section, is that the
combination of physical exposures and psychosocial exposures presented
increased risk. A level of physical risk that is acceptable in a
psychosocially benign work environment can combine with elevated levels
of psychosocial risk to cause disorders.
Finally, many of the studies cited in this article confuse cause
with effect. To continue with Dr. Nachemson's citation, Valfors
concluded that the measured differences in work satisfaction were the
cause of the low back pain episodes, when it is just as likely that the
LBP itself affected patients assessment of their work satisfaction (see
Linton, 2000, Ex. 26-642).
These three errors, together or individually, characterize many of
the studies in the Nachemson article. In sum, this review, while useful
in collecting a wide variety of studies addressing the complex issues
of low back pain, disability, and management, does not demonstrate that
physical workplace factors are not involved in the etiology of LBP. Nor
does it demonstrate that workplace interventions directed towards
reduction of biomechanical risk factors would be ineffective. His
citation of the Daltroy (Daltroy et al., 1997, Ex. 38-57) training
intervention in the postal service, for example, is not a refutation of
the central causal role of biomechanical exposures in the etiology of
back injury. Rather, it is emblematic of the general failure of ``back
schools'', when introduced in the absence of measures directed towards
control of physical risk factors. Dr. Nachemson, himself, states in
this review: ``[I]t is obvious that certain types of lifts and working
positions should be avoided and this in particular applies to twisted
lifts.'' Ideally, this review will advance the development of more
effective intervention techniques that address the combination of risk
factors presented by Dr. Nachemson.
Waddell & Burton 2000 (Ex. DC-151-A). This thorough review of
management protocols for LBP includes evaluation of epidemiological and
clinical studies addressing etiology of LBP. Because the review and
recommendations focus primarily on medical management issues, it is not
surprising that it concentrates on the psychosocial factors involved in
pain perception, sickness absence, disability and return-to work. Most
of the studies addressed above acknowledge the importance of
psychosocial factors in medical management issues, not only for LBP but
also for other musculoskeletal disorders. The evidence reviewed above
corresponds with these authors' conclusions that low job satisfaction,
``unsatisfactory psychosocial aspects of work'' and individual
psychosocial findings are risk factors for onset of LBP, health care
use and work loss, but the size of that association is small to modest
(strong evidence). The authors also noted that physical demands of work
(manual materials handling, lifting, bending, twisting, and whole body
vibration) can be associated with onset of LBP, increased LBP reports,
symptom aggravation, and back ``injury'' (authors'' quotes). However,
they find that the association ``appears to be'' weaker than those of
individual, non-occupational and unidentified factors (strong
evidence).
The authors make an elementary error in ascribing potential LBP
causation only to dynamic back activities. Their noting the high
prevalence of LBP in non-dynamic jobs, and even in the unemployed, is,
of course, related to the well-established research findings that
sedentary and constrained postures are also physical risk factors for
back disorders (Putz-Anderson, 1991, Ex. 26-1255, Hoogendoorn et al.,
1999, Ex. 38-81, Burdorf & Sorock, 1997 Ex. 502-232).
More importantly, the studies used to provide ``strong evidence''
for various conclusions are sometimes categorized as being of high
quality when, in fact, they violate some of the important
epidemiological design criteria cited above. In particular, in making a
case for primarily psychosocial causation, the authors used studies
that measured biomechanical exposures inadequately (e.g., Bigos et al.,
1991b, Ex. 26-1242, and others reviewed above) or studies that did not
include both biomechanical and psychosocial factors in statistical
modeling (Macfarlane et al., 1997, Ex. 500-41-91, Papageorgiou et al.,
1997, Ex. 32-241-3-41). Several reviews are cited that, on closer
examination, are only modest in their assessment of both psychosocial
and biomechanical risk contribution, noting the problems with study
design and, especially, the relatively few studies that assessed both
exposures adequately and at equal levels of precision (Burdorf &
Sorock, 1997, Ex. 500-232, Bongers et al., 1993, Ex. 26-1292, Davis &
Heaney, 2000).
Conclusions
Based on the rulemaking testimony, scientific studies, and
literature reviews considered in this section, OSHA concludes that the
evidence contained in the record supports a combined contribution of
biomechanical and psychosocial risk factors to the onset, development
and prolongation of MSDs. Biomechanical contributions to the etiology
of work-related MSDs have been demonstrated to be more consistent than
psychosocial factors across different study populations, and most well-
designed studies reported stronger associations between exposure to
biomechanical risk factors and an increased MSD prevalence or incidence
than has been observed for psychosocial factors. However, it is not
possible to determine the relative strength of association between
biomechanical and psychosocial factors with any precision because of
differences in measurement techniques used in the various studies to
assess biomechanical and psychosocial factors, and because of the
different ways in which psychosocial factors are defined by various
investigators. Most importantly is the finding by several investigators
that
[[Page 68531]]
biomechanical and psychosocial factors influence MSD risk in
independent fashon, which suggests that reductions in biomechanical
exposures absent any change in psychosocial influences should reduce
the risk of work-related MSDs.
Findings from published literature reviews of studies that conform
to the epidemiologic design principles discussed above are consistent
with the Agency's conclusions. Four reviews (Burdorf, Ex. 502-232,
Punnett, 38-13, Lagerstrom, Ex. 38-102, NAS, Ex. 26-37) reported that
biomechanical risk factors generally showed stronger and/or more
consistent associations with elevated MSD prevalence or incidence than
did psychosocial factors.
Three reviews reached an opposite conclusion (Linton, Ex. 26-642,
Nachemson, Ex. 32-241-3-31, Waddell, DC-151-A); however, these reviews
relied more heavily on studies where biomechanical factors were not
evaluated at all, were evaluated in jobs having little variance in
physical load, or were evaluated at different analytical levels or with
less precision, or than psychosocial factors. All of these design flaws
bias results towards increased psychosocial effects in modeling. It is
on the basis of these reviews and the underlying studies that the
Chamber of Commerce, Gibson, Dunn & Crutcher, and several of their
scientific witnesses base their conclusion that psychosocial factors
outweigh the importance of biomechanical factors in the etiology of
MSDs. Accordingly, OSHA is not persuaded by these arguments, and finds
the preponderance of evidence supports a multifactorial model of MSD
causation involving both biomechanical and psychosocial factors acting
independently on risk.
Moreover, testimony and evidence presented above suggests that
biomechanical and psychosocial risk factors are, to a degree,
inextricable (Punnett, testimony, Tr. 868, Kerr et al., 2000, Ex. 38-
82). The degree of influence each exerts on MSD risk is in large part
determined by company characteristics and work organization, and their
very separation is somewhat artificial. The final rule's focus on
reducing exposures to biomechanical risk factors reflects the
intervention strategy that has been emphasized in the literature and
implemented by many sophisticated companies. Simply less is known about
how to intervene effectively on psychosocial factors. However, this
does not mean that biomechanical intervention will have no effect on
psychosocial factors in the wortkplace. Because of the correlation and
interactions between biomechanical and psychosocial factors in their
associations with MSD outcomes, interventions focused towards
biomechanical stressor reduction are likely to have a positive effect
on levels of psychosocial stress. The arguments of Bellamy and Vendor,
above (testimony) are addressed by the reality of this close
correlation between stressor types.
The intervention literature demonstrates that the very fact of a
company's undertaking even a limited program to control biomechanical
exposures is, de facto, also a psychosocial intervention. If workers
report MSD symptoms and the company responds with workplace
alterations, medical intervention, training, and the other program
elements in the final rule, this response often represents a reduction
in excessive psychological demands, an increased sense of control, and
an improvement in the social support structure of the workplace. In
Sweden, Kvarnstrom (1992, Ex. 38-69) found that changes in the physical
work characteristics, combined with changes in the psychosocial work
environment (increased variety, decision-making latitude, and
individual control over the work situation) in a small department of a
large, multi-national company greatly reduced the high rate of
absenteeism and turnover due to musculoskeletal disease. In the United
States, Smith and Zehel (1992, Ex. 38-70) reported that employee focus
groups identified the need for physically-oriented engineering changes
as well as psychosocial changes in a meat-processing plant; the
combined intervention resulted in decreased physical symptoms for part
of the work force. Worker participation in problem identification and
solution development is a central feature of many successful approaches
to work environment change and is at the core of the proposed rule. For
example, Pasmore & Friedlander (1982, Ex. 38-71), addressing an
outbreak of upper extremity disorders in a United States electronic
assembly facility, designed an intervention in which the employees
determined the data to be collected and solutions based on these data.
While this level of employee involvement focused on reducing
biomechanical risk factors, it also increased employee participation
and task control and altered role relationships within the
organization.
A number of witnesses testified at the hearing that ergonomic
programs designed to address biomechanicla factors have positive
effects on psychosocial factors that have been implicated in MSD
etiology. Dr. Warren explained why this is the case:
I think what happens hypothetically and in my experience is that
when you control a biomechanical workpalce factor, you are de facto
making a small psychosocial intervention in the workplace.
When * * * somebody says [``]my back hurts[''] and it's followed
* * * immediately by [``]and nobody cares[''], you know that there's
a psychological problem in that workpalce. So I think that, yes, * *
* a control of a biomechanical risk factor with no change in a
psychosocial environment would reduce the chance of injury, but that
it would probably also change the psychosocial environment to a
small degree. [Tr. 1265]
Dr. Rosecrance (Tr. 2319-20) presented a specific example. He noted
that the biomechanical intervention in his study of the Cedar Rapids
Gazette resulted not only in reductions of MSDs, but also improvements
in the company social structure.
Mr. Dave Alexander believed that the employee participation
provision of the proposed standard would address psychosocial issues:
* * * the opportunity for worker participation in the form of
contributing information, suggesting solutions, having a mechanism
to report problems would, in fact, tie in with the psychosocial
issues that would be important in the workplace. [Tr. 2713-2714]
Similarly, Dr. Silverstein testified that providing workers with basic
information on MSDs and employee involvement in the ergonomics program
increases the decision latitude for workers [Tr. 17445].
These studies and testimony indicate that the basic precepts of
management commitment and employee participation contained in the final
rule, while forming the administrative infrastructure of an ergonomics
program focused on physical risk abatement, has the potential to have
positive effects on the psychosocial characteristics of the work
environment.
6. Final Rule's Consistency With Medical Guidelines
Several commenters questioned whether the program elements of
OSHA's final rule were consistent with existing medical practice
guidelines, primarily with respect to diagnosing and treating low back
pain, but also diagnosing and treating other MSDs. For example, when
referring to the Agency for Health Care Policy and Research (AHCPR) low
back pain guidelines, Gibson, Dunn and Crutcher stated that the review
of evidence published with the guidelines
contradicts OSHA's ergonomic hypothesis that work causes physical
injury, contradicts OSHA's view that ``ergonomic'' interventions can
alleviate workplace pain, and contradicts
[[Page 68532]]
OSHA's prescription for rest as a response to back pain. [Ex. 500-
118]
OSHA disagrees with these commenters. In reviewing the record, OSHA
finds that the final rule is consistent with the medical literature,
including the AHCPR guidelines, the American College of Occupational
and Environmental Medicine (ACOEM) Occupational Medicine Practice
Guidelines (Ex. 38-234), The Royal College of General Practitioners'
Clinical Guidelines for the Management of Acute Low Back Pain (Royal
College guidelines) (Waddell et al. 1999; Ex. 32-241-3-38), the Faculty
of Occupational Medicine's Occupational Health Guidelines for the
Management of Low Back Pain at Work (British guidelines) (Ex. 500-118-
2), and other evidence-based medical practice.
The first assertion, that the AHCPR guidelines ``contradict[ ]
OSHA's ergonomic hypothesis that work causes physical injury'' is
incorrect for several reasons. The AHCPR guidelines acknowledge that
* * * several studies have identified an increased incidence of low
back problems among individuals whose work involves heavy or
repetitive lifting, exposure to total body vibration (from vehicles
or industrial machinery), asymmetric postures, and postures
sustained for long periods of time. [Ex. 32-241-3-93]
The guidelines also recognize that
Other biomechanical research suggests that certain postures and
activities increase the mechanical stress on the spine. It is not
clear whether these mechanical stresses are the cause of low back
problems. However, once symptoms are present, mechanical stresses
correlate with worsening of symptoms. Prolonged sitting and postures
that involve bending and twisting have been shown to increase the
mechanical stress on the spine according to pressure measurements in
lumbar intervertebral discs. Heavy lifting also appears to increase
mechanical stress on the spine, but this stress can be reduced if
the lifted object is held close to the body rather than at arm's
length. [Ex. 32-241-3-93]
These conclusions are clearly consistent with the conclusions of the
Health Effects section of the final rule that biomechanical factors are
associated with low back pain. It must be recalled that the AHCPR
guidelines were
* * * intended to provide primary care clinicians with information
and recommended strategies for the assessment and treatment of acute
low back problems in adults. [Ex. 32-241-3-93]
They were not intended to provide a comprehensive review of work-
related low back pain, ergonomics or low back pain prevention. There
are few references to ergonomics, and the guidelines promotes the
utility of ergonomics in return to work decision making by stating
that: ``Several ergonomic guidelines on lifting and materials-handling
tasks are available to help the clinician provide ranges of activity
alterations at work.'' (Ex. 32-241-3-93)
Finally, the AHCPR guidelines (Ex. 32-241-3-93) do not suggest that
patients with acute low back pain immediately return to work involving
physical factors that may stress the spine. Rather they advise
appropriate activity modification to assist in the recovery process.
AHCPR guidelines Activity Recommendations panel findings and
recommendations state: (1) ``Patients with acute low back problems may
be more comfortable if they temporarily limit or avoid specific
activities known to increase mechanical stress on the spine, especially
prolonged unsupported sitting, heavy lifting, and bending or twisting
the back while lifting. (Strength of Evidence = D.);'' and (2)
``Activity recommendations for the employed patient with acute low back
symptoms need to consider the patient's age and general health, and the
physical demands of required job tasks. (Strength of Evidence = D.)''
As to the duration of activity modification, the AHCPR guidelines
demonstrate an understanding of the impact that the physical demands of
work have on recovery and modified activity. The guidelines state that
``The nature and duration of limitations will depend on the clinical
status of the patient and the physical requirements of the job.''
Several other components of the final rule are supported by AHCPR
recommendations, including the use of job hazard analysis and medical
management involving communication with the HCP. Pertinent AHCPR
guidelines statements are as follows: (1) ``In recommending activity
modifications for patients who work, the clinician may find it helpful
to obtain from the employer a description of the physical demands of
required job tasks,'' and (2) ``The panel recommends that clinicians
help patients establish activity goals, in consultation with their
employer when applicable.''
As with the AHCPR guidelines (Ex. 32-241-3-93), the commenters
cited above did not accurately represent the findings of the Royal
College guidelines (Ex. 32-241-3-38) and British guidelines (Ex. 500-
118-2) in criticizing OSHA's proposal. They also failed to acknowledge
evidence and recommendations from these reports that are consistent
with the final rule.
The Royal College guidelines (Ex. 32-241-3-38) were developed for
the purpose of disseminating evidence-based recommendations on the
management of acute low back pain to clinicians. The Royal College
guidelines do not purport to relate to, nor were they focused on, the
same purpose as OSHA's proposal, that is to reduce MSDs and control MSD
hazards in the workplace. These guidelines do not contain information
on evidence based conclusions on ergonomics or low back pain
prevention. Several elements of the proposal are supported by the Royal
College guidelines (Ex. 32-241-3-38). For example, under Initial
Assessment Methods, they recommend: ``The patient's age, the duration
and description of symptoms, the impact of symptoms on activity and
work, and the response to previous therapy are important in the care of
back problems.'' Under Information to Patients, the guidelines state:
``About 10% of patients will have some persisting symptoms a year
later, but most of them can manage to continue with most normal
activities. Patients who return to normal activities feel healthier,
use less analgesics and are less distressed than those who limit their
activities.'' The Royal College guidelines suggest that most workers
can manage with most normal activities, but do not suggest that this
includes extremely physical tasks that cause very significant
mechanical loading to the lumbar spine and are associated with elevated
risks of low back pain.
Similarly, the purpose and findings of the British occupational
health low back pain guidelines (Ex. 500-118-2) have also been
misrepresented (e.g., Ex. 32-241-3-20). The British guidelines state:
``These guidelines represent the main recommendations and evidence
statements derived from a detailed Evidence Review and developed by a
multidisciplinary group of practitioners. They concern the clinical
management of workers affected by non-specific low back pain, including
advice on placement, rehabilitation and measures for prevention.'' The
British guidelines further clarify that they were not intended to
disseminate information regarding workplace health and safety, job
design, and ergonomics when they state: ``They focus on actions to be
taken to assist the individual and do not specifically cover legal
issues, health and safety management, job design and ergonomics.''
Again, this is a different focus than the proposal, and conclusions
should be interpreted in that light. Under evidence review methods, the
British guidelines state:
In view of the occupational health focus of the guidelines and
the present review, the following areas were excluded from the
review, except where they impact directly on the guideline
recommendations: chronic
[[Page 68533]]
intractable pain, long-term disability and pain management
programmes; spinal surgery and post-operative states; primary
ergonomic interventions. [Ex. 32-241-3-93]
The British guidelines (Ex. 500-118-2) acknowledge the role of work
in contributing to low back pain in its own preface. In reviewing
challenges for the review the authors state: ``The need for everyone to
recognize that work is only one contributor to back pain but that back
pain whatever its cause can, if poorly managed, have a devastating
effect on a person's ability to work.'' The review goes on to classify
evidence based literature recommendations using the following
classification scenarios:
***Strong evidence--provided by generally consistent findings in
multiple, high quality scientific studies.
**Moderate evidence--provided by generally consistent findings in
fewer, smaller or lower quality scientific studies.
*Limited or contradictory evidence--provided by one scientific
study or inconsistent findings in multiple scientific studies.
--No scientific evidence--based on clinical studies, theoretical
considerations and/or clinical consensus.
Several British guidelines (Ex. 500-118-2) findings are consistent
with the final rule. With respect to the relationship of physical work
factors and work-related low back pain, the guidelines report the
following evidence based findings: There is strong evidence that
Physical demands of work (manual materials handling, lifting,
bending, twisting, and whole body vibration) can be associated with
increased reports of back symptoms, aggravation of symptoms and
``injuries.'' [Ex. 500-118-2]
These guidelines therefore acknowledge potential for physical work
factors to precipitate low back pain episodes, and recognize some
evidence of a cumulative effect of spinal loading. In addition,
management of work-related low back pain, as noted in the AHCPR low
back pain guidelines, may reasonably include elements similar to those
in the OSHA final rule, such as
* * * temporarily limit[ing] or avoid[ing] specific activities known
to increase mechanical stress on the spine, especially prolonged
unsupported sitting, heavy lifting, and bending or twisting the back
while lifting. [Ex. 32-241-3-93]
In summary, the British guidelines (Ex. 500-118-2) state that there is
moderate evidence that ``From an organisational perspective, the
temporary provision of lighter or modified duties facilitates return to
work and reduces time off work.''
The British guidelines (Ex. 500-118-2) go on to cite other
conclusions about work and low back pain using evidence based
literature reviews (Evidence) and consensus opinion (Recommendation).
In making recommendations on prevention and case management, the
authors advise the ``need to be directed at both physical and
psychosocial factors.'' If physical work is not harmful and it does not
contribute to low back pain, then why would the authors advise
addressing the physical task factors of work in prevention efforts?
Similarly, if physical characteristics of work are not significant
issues for workers who return to work after developing a low back
disorder, then why do the authors state the following?
There is a pragmatic argument that individuals at highest risk
of LBP should not be placed in jobs that impose the greatest
physical demands. The basic concern is that workers with physically
(or psychologically) demanding work report rather more low back
symptoms, have more work-related back ``injuries'' and lose more
time off work with LBP. Even if physical demands of work may be a
relatively modest factor in the primary causation of LBP (see
Background above), people who have LBP (for whatever cause) do have
more difficulty managing physically demanding work (T3: (Muller et
al.1999) T2: (Waddell 1998)). It may be argued, therefore, that
avoiding putting people at highest risk of recurrent LBP and
sickness absence into more physically demanding work would be in the
interests of the individual worker, the employer and the total
societal burden of LBP. [Ex. 500-118-2]
Similarly, the ACOEM guidelines (Ex. 38-234) agree with the observation
that specific physical work factors are associated with certain work-
related MSDs.
One of the criticisms raised by a commenter was the limited
reference to the Cochrane Collaboration Back Review Group in low back
sections of the Health Effects section of the preamble to the proposed
rule. However, as a significant contributor to this effort, Dr.
Nachemson clarified that neither work-related back pain nor ergonomics
were the focus of these reviews (Tr. 6779).
Although Dr. Nachemson questioned OSHA's findings of the
relationship of work to the development of work-related low back
disorders, he contradicts this in the chapter he authored for the
International Society for the Study of the Lumbar Spine, entitled
``Future of Low Back Pain'' (Wiesel et al. 1996, Ex. 26-1620). The
chapter has a table compiled on the effects of external load on low
back structures. The table lists extreme loading activity, several
hours of hard training, extreme body position, as having negative
influences on muscle, cartilage, and disc.
Dr. Stanley Bigos admitted that physical work factors could result
in the development of low back pain in an exchange with one of the
questioners.
MS. GWYNN: Doctor, you believe, do you not, that lifting and
bending while lifting and twisting while lifting can aggravate low
back pain?
DR. BIGOS: I believe that it can bring on symptoms in people who
have had prior back problems. And perhaps, it could bring on
symptoms of people who haven't, depending upon the condition they
are in. [Tr. 6916]
Along other lines, some commenters raised issues with OSHA's
inclusion of symptoms in the definition of an MSD. Gibson, Dunn and
Crutcher stated that:
These sensations that the agency treats as tantamount to
musculoskeletal injury are ubiquitous in the general population and
do not warrant interference by the agency. [Ex. 500-118]
OSHA does not agree with this argument. OSHA is not attempting to
regulate common symptoms. Rather, OSHA has proposed strategies to
modify physical workplace factors that are associated with the
development of MSDs, when the physical factors at work are present in
frequency, intensity, and/or duration likely to be responsible for
causing observed MSDs. As required in the final rule, the employer's
responsibility is that it must evaluate employee reports of MSD signs
and symptoms to determine whether an MSD incident has occurred. The
evaluation may include an evaluation by an HCP to determine the nature
of the condition and assist the employer in evaluating the work-
relatedness of the MSD. Many employers presently act in a very similar
manner when an employee reports a potential problem. The employer may
perform an accident or incident investigation, offer temporary modified
duty, correct the problem, and/or refer the employee to a HCP for
evaluation.
Gibson, Dunn, and Crutcher also suggested that paying attention to
subjective complaints would lead to inaccurate diagnoses. They state
that:
One of the challenges presented by MSDs is that, in order to
diagnose an affliction (in an effort to determine what response is
required to comply with the proposed standard), an employer or the
employer's physician must rely principally, if not solely, on
subjective reports of pain from employees. [Ex. 500-118]
These assertions are incorrect, and are not consistent with medical
literature and opinion. A worker's medical history, including
subjective reports like pain, is a key element that has been
[[Page 68534]]
utilized since the beginnings of medicine to help physicians diagnose
medical conditions. The AHCPR guidelines emphasize the role of the
medical history when they state:
A few key questions on the medical history can help ensure that
a serious underlying condition, such as cancer or spinal infection,
will not be missed * * * Symptoms of sciatica (leg pain) or
neurogenic claudication (walking limitations due to leg pain)
suggest possible neurologic involvement. Pain radiating below the
knee is more likely to indicate a true radiculopathy than pain
radiating only to the posterior thigh. A history of persistent
numbness or weakness in the leg(s) further increases the likelihood
of neurologic involvement. The articles indicate that cauda equina
syndrome can be ruled out with a medical history that ascertains the
absence of bladder dysfunction (usually urinary retention or
overflow incontinence), saddle anesthesia, and unilateral or
bilateral leg pain and weakness. [Ex. 32-241-3-93]
The AHCPR guidelines go on to clarify that the examination is used to
confirm clinical impressions derived from the medical history,
including pain characteristics:
The physical examination supplements the information obtained in
the medical history in seeking an underlying serious condition or
possible neurologic compromise. [Ex. 32-241-3-93]
The AHCPR low back pain guidelines also indicate that ``The physical
examination is less useful than the history in searching for underlying
serious conditions.'' Thus OSHA's approach to the use of employee
symptoms is similar to the AHCPR rigorous analysis of the literature on
acute low back pain evaluation and treatment that concluded that
symptoms and history give important information to diagnose and manage
adults with acute low back pain.
Both the Royal College and British guidelines support the role of
history, including symptoms, in the diagnosis and management of low
back pain. The British guidelines state:
The patient's age, the duration and description of symptoms, the
impact of symptoms on activity and work, and the response to
previous therapy are important in the care of back problems. (B:
Moderate research based evidence). [Ex. 500-118-2]
The guidelines confirm AHCPR recommendations by indicating:
The initial clinical history can identify `red flags' of
possible serious pathology. Such inquiries are especially important
in patients over age 55. (B: Moderate research based evidence). [Ex.
500-118-2]
OSHA's approach, in particular the acknowledgment of worker
symptoms, parallels this literature based analysis.
Further validation of the importance of symptom reporting for low
back pain comes from the ACOEM guidelines (Harris et al. 1997; Ex. 502-
240). The ACOEM guidelines included peer review by Dr. Stanley Bigos,
expert witness for UPS and Anheuser-Busch and others. The following
quotes are excerpted from the guidelines:
A focused medical history, work history, and physical
examination are generally sufficient to assess the worker with a
complaint of an apparently job related disorder. [Ex. 502-240]
In this assessment, certain patient responses and findings raise the
suspicion of serious underlying medical conditions.
The patient's description of the mechanism of injury (so far as
is known), his or her presenting symptoms, the duration of symptoms,
exacerbating factors, and the history of previous episodes will help
define the problem. [Ex. 502-240]
In Chapter 14, the ACOEM guidelines state:
Thorough medical and work histories and a focused physical
examination are sufficient for the initial assessment of the worker
with a complaint of potentially work-related low back symptoms. [Ex.
502-240]
These statements from clinical medicine practice guidelines provide
further support for the use of symptoms as a trigger in the final rule.
The practice guidelines make use of the patient history and reports of
symptoms and take a consistent approach to the physical examination
referent to patients with low back pain.
This approach is consistent with the one medical text brought to
OSHA's attention. The International Society for the Study of The Lumbar
Spine publishes a text entitled ``The Lumbar Spine'' (Wiesel, et al.
1996; Ex. 26-1620). In Chapter 3 on clinical evaluation of low back
pain by Jeremy Fairbank and Hamilton Hall (History taking and physical
examination: Identification of syndromes of back pain), the authors
state:
Conventional western medical therapy is practiced on the basis
of a diagnosis that is made from a synthesis of information acquired
from the patient's history, physical examination, and special
investigations. Back pain is a common presenting symptom, and its
diagnosis should be approached in the same manner as that of any
other symptom. [Ex. 26-1620]
They further state that
A detailed history obtained from the patient is essential for
making a diagnosis, assessing disability, and dictating management.
Time spent listening to the patient is not wasted. Back pain has a
wide variety of causes, and many of these can be revealed during
history taking. [Ex. 26-1620]
providing support that
Objective evidence obtained on physical examination should
enhance and support the diagnostic hypotheses arising from the
patient's history. [Ex. 26-1620]
The authors go on to propose a classification system for low back
pain (Pynsent-Fairbank-Hall Classification of Extraspinal Pain), which
is primarily based upon patient symptoms. The acknowledgment of the
importance of symptoms in this text is of particular interest to OSHA
due to the fact that two principal expert witnesses who testified on
behalf of UPS and others that symptoms are not meaningful, Dr. Stanley
Bigos and Dr. Alf Nachemson, are members of The International Society
for the Study of The Lumbar Spine, the organization that published the
above text.
The classification of low back pain primarily upon patient symptoms
is similar to the approach used by the Quebec Task Force (1987; Ex. 26-
494). Dr. Nachemson also served as a member of the task force for this
publication. The Quebec classification included 11 categories, with 1-
4, 8, 9 and 10 based upon symptoms.
The American Medical Association, in its Guides to the Evaluation
of Permanent Impairment, 4th edition, (Ex. 38-246) also include
symptoms in classifying impairment. In particular, Table 72 in that
publication contains a Diagnosis Related Estimate for Lumbosacral
Category II: Minor Impairment (5% whole person impairment). The
guidance used by the AMA for this is ``The clinical history and
examination findings are compatible with a specific injury or illness.
The findings include significant intermittent or continuous muscle
guarding that has been observed and documented by a physician,
nonuniform loss of range of motion, or nonverifiable radicular
complaints. There is no objective sign of radiculopathy and no loss of
structural integrity.'' There is similar guidance for the cervical
spine.
Guidelines for diagnosis and treatment of low back pain that have
been published in the United States include the AHCPR guidelines (Ex.
32-241-3-93) and the ACOEM guidelines (Ex. 38-234). These will be
addressed in the discussion on rest and activity to follow in this
section.
It must also be recognized that low back pain is not the only
potentially covered MSD, and other potential MSDs may present as
symptoms only. For example, it is clear that patients with CTS may have
symptoms of numbness without any physical findings (Erdil and
[[Page 68535]]
Dickerson 1997, Ex. 502-18; Katz et al. 1991, Ex. 38-101; Moore 1992,
Ex. 26-985). Of significance, commonly utilized physical signs to
clinically diagnose carpal tunnel syndrome, such as the Tinel's test
and Phalen's sign, do not have as high a sensitivity or specificity as
the Hand Diagram (Katz and Stirrat 1990; Ex. 500-121-33), a symptom
based tool. Clearly, utilizing symptoms to identify possible cases of
carpal tunnel syndrome and other MSDs is consistent with the knowledge
based upon reviewing the medical literature.
Dr. Malcolm Jayson argued that
* * * if a person has pain in the knee, the most effective form of
treatment is knee exercises. When we rehabilitate back problems we
prescribe[] exercises with a progressive regime to increase physical
capacity. There is now overwhelming evidence that exercise is good
for back problems and damaged joints and rest is harmful. [Ex. 32-
241-3-9]
However, nowhere does OSHA state that all exercise is harmful, nor does
it support rest as the treatment for MSDs. With regard to work factors
like repetition, it is important to recognize that biomechanical
factors that are present in a sufficient intensity, duration, and/or
frequency to cause or contribute to an MSD are addressed. In these
circumstances, OSHA recommends modification of exposure to these
factors. It is clear that, when excessive, repetition and other cited
work factors can cause MSDs. Several studies were presented in the
Health Effects Section of the final rule to demonstrate the pathogenic
mechanisms through which physical work factors can be responsible for
causing or contributing to certain MSDs identified in the epidemiologic
review. Unfairly, this statement simplifies physical factors in work
settings as solely characterized by repetition, without considering the
frequency, duration, and periodicity of the repetitive activities. In
addition, it ignores other factors that have potential to cause MSDs in
the workplace, such as excessive force, awkward posture, contact
stress, and vibration. Also neglected is the observation that
combinations of factors like force, posture, etc. with repetition, may
compound the effect of repetition on musculoskeletal tissues. Finally,
the statement does not differentiate types of tissue affected and
whether the tissue is healthy or damaged.
In the preface to The American Academy of Orthopedic Surgeons' book
entitled ``Repetitive Motion Disorders of the Upper Extremity'' (Gordon
et al. 1995; Ex. 26-1399), the editor states:
There is overwhelming evidence that the number of reported cases
of repetitive motion disorders is rapidly growing. These disorders
have become an extremely costly public health issue. Although some
individuals believe that the underlying issue may be improper
reporting or false claims of a medical problem, the organizers and
most of the participants believe that for the vast majority of
cases, there is an underlying physiologic insult to one or more of
the various tissues involved.
The text goes on to cover epidemiologic evidence; pathophysiology
of biomechanical loads, connective tissue, muscle and nerve. Chapters
on rehabilitation of the wrist, elbow and shoulder all indicate that
time limited periods of rest may be indicated for acute MSDs. The book
is the result of a workshop organized by the National Institute of
Arthritis and Musculoskeletal and Skin Disease, NIH. Co-sponsors
included NIOSH, CDC, Orthopedic Research and Education Foundation, the
National Center for Medical Rehabilitation Research, and others. One
expert witness Dr. Stanley Bigos, who testified on behalf of one
industry group organized in opposition to OSHA's proposed standard in
general, is a member of AAOS.
In June 1998, Clinical Orthopedics and Related Research (Exs. 26-
1310, 26-1322, 26-1316) covered Cumulative Trauma Disorders of the
Upper Extremity through a joint sponsorship of the Association of Bone
and Joint Surgeons, the Academic Orthopedic Society, the Hip Society,
the Musculoskeletal Tumor Society, and the Knee Society. This text
again covered sections regarding the effects of physical work factors
(i.e. repetition) on nerve, muscle, joints, and certain clinical
conditions.
Similarly, the National Academy of Sciences, in 1999, (Ex. 26-37)
published the results of a workshop they sponsored on work-related
MSDs. While there was some variance in opinions about the contribution
of physical work factors to MSDs, there was agreement among most that
physical work factors contribute to MSDs. ``MSDs are multifactorial,
with work and biomechanical aspects of work being important
contributors.'' The NAS reviewers also explained the concepts behind
temporary rest or activity modification for injured tissues.
Contrary to the view of NAS, Dr. Stanley Bigos provided the
following comment:
Contrary to ergonomists' beliefs, usage is a prerequisite to
health--using the body, even vigorously using the body, is not
intrinsically harmful. That is why repetitive motion that fatigues
musculoskeletal tissues is medically prescribed, to the point of
being the preferred method of treatment even of tissues that have
sustained traumatic injury or age-related degeneration. Properly
conditioned; a traumatically injured joint may be restored to full
function by the protection of muscles stronger than before the
injury. [Ex. 32-241-3-4]
Dr. Bigos' statement that ``repetitive motion that fatigues
musculoskeletal tissues is medically prescribed, to the point of being
the preferred method of treatment even of tissues that have sustained
traumatic injury or age-related degeneration,'' while having elements
of validity, again fails to look at the various work-related MSDs as
well as the stage and severity of the condition. There is supporting
literature and consensus, including clinical practice guidelines (e.g.
ACOEM; Ex. 38-234) that recommend periods of splinting and rest for
MSDs like acute tendonitis or stenosing tenosynovitis, DeQuervain's
disease and carpal and cubital tunnel syndromes. A comparison could be
made to a patient who experiences an acute myocardial infarction with
muscle damage. In this scenario, rehabilitation often includes
carefully controlled exercise appropriate to the stage of recovery and
level of function of the remaining heart muscle. It would not be
reasonable to presume that a patient one day after a significant
myocardial would be improved if forced to run a marathon. Neither would
a worker benefit from intensive and uncontrolled exercise after the
onset of an acute MSD with significant inflammation, degeneration and
loss of function.
The same commenters stated that OSHA's use of the term ``rest'' in
the proposal implied that OSHA recommends or promotes bed rest for
workers with MSDs. This statement is incorrect and fails to recognize
the purpose and application of the standard. This standard is not
intended as a guideline for the medical treatment of MSDs. Medical
treatment is left to the licensed health care provider, utilizing sound
medical judgement, and evidence based literature and clinical practice
guidelines.
What OSHA did intend when it used the term ``rest'' was appropriate
activity modification. The standard supports return to work where there
are effective controls of biomechanical factors causing or contributing
to the MSD. The preamble to the proposal stated:
Although some covered MSDs are at such an advanced state that
complete removal from the work environment is the appropriate
treatment, it should usually be the recommendation of last resort.
Where appropriate, work restrictions that allow the employee to
continue working (e.g., in an
[[Page 68536]]
alternate job, or by modifying certain tasks in the employee's job
to enable the employee to remain in that job) are preferable during
the recovery period.
Dr. Stanley Bigos argued that the proposed ergonomics rule was at odds
with the recommendations of the AHCPR guidelines, in that the proposed
rule recommended rest, reduced work, and inactivity in response to
pain, while the AHCPR guidelines recommend increased activity and
conditioning (Ex. 32-241-4).
The AHCPR guidelines (Ex. 32-241-3-93) do recommend that adults
with acute low back pain maintain activity. However, the guidelines do
not suggest that patients with acute low back pain immediately return
to work involving physical task factors that may stress the spine.
Rather they advise appropriate activity modification to assist in the
recovery process. AHCPR guidelines Activity Recommendations panel
findings and recommendations state: ``Patients with acute low back
problems may be more comfortable if they temporarily limit or avoid
specific activities known to increase mechanical stress on the spine,
especially prolonged unsupported sitting, heavy lifting, and bending or
twisting the back while lifting. (Strength of Evidence = D.);'' and,
``Activity recommendations for the employed patient with acute low back
symptoms need to consider the patient's age and general health, and the
physical demands of required job tasks. (Strength of Evidence=D.)''
The AHCPR guidelines acknowledge that
several studies have identified an increased incidence of low back
problems among individuals whose work involves heavy or repetitive
lifting, exposure to total body vibration (from vehicles or
industrial machinery), asymmetric postures, and postures sustained
for long periods of time.'' [Ex. 32-241-3-93]
The guidelines also recognized that
Other biomechanical research suggests that certain postures and
activities increase the mechanical stress on the spine. It is not
clear whether these mechanical stresses are the cause of low back
problems. However, once symptoms are present, mechanical stresses
correlate with worsening of symptoms. Prolonged sitting and postures
that involve bending and twisting have been shown to increase the
mechanical stress on the spine according to pressure measurements in
lumbar intervertebral discs. Heavy lifting also appears to increase
mechanical stress on the spine, but this stress can be reduced if
the lifted object is held close to the body rather than at arm's
length.'' [Ex. 32-241-3-93]
As to the duration of activity modification, the AHCPR guidelines
(Ex. 32-241-3-93) demonstrate an understanding of the impact that the
physical demands of work have on recovery and modified activity. They
state that ``The nature and duration of limitations will depend on the
clinical status of the patient and the physical requirements of the
job.''
While the AHCPR guidelines (Ex. 32-241-3-93) did not find evidence
that bed rest was beneficial for the majority of individuals with acute
low back pain, the panel did acknowledge that, in some circumstances,
bed rest may be required for select patients with acute low back pain
(``The majority of low back patients will not require bed rest. Bed
rest for 2 to 4 days may be an option for patients with severe initial
symptoms of primarily leg pain.'')
Program elements in OSHA's proposal are also consistent with the
British guidelines, that state that there is moderate evidence that
From an organisational perspective, the temporary provision of
lighter or modified duties facilitates return to work and reduces
time off work. [Ex. 500-118-2]
Some commenters appeared to confuse the concepts relevant to the
practice of sports medicine with concepts relevant to the prevention of
MSDS in workers. For example, Gibson, Dunn & Crutcher state
Increase in physical activity (compared to past activity level)
is a guiding principle in musculoskeletal rehabilitation, and has
been the primary intervention and treatment in many musculoskeletal
disorders. These treatment protocols include many of the physical
stresses that OSHA recommends avoiding. [Ex. 500-118]
This again is an overly simplistic statement, since there are
differences in the intensity, duration, and/or frequency of guided
rehabilitation of an injury that is tailored to the individual's type
of injury, severity of the condition, stage of rehabilitation and the
individual's conditioning, as opposed to intensity, duration, and/or
frequency of physical job factors that are based upon delivery of goods
or services and have no bearing upon individual capabilities or
injuries. Dr. Tapio Videman, another expert witness for the UPS
attempted to explain the importance of physical activity as follows:
Sports medicine--and much of modem mainstream medicine--views
physical loading as a means of increasing fitness, strength, and
function, and is part of most related intervention today. Why would
physical loading be harmful in work but beneficial in leisure time?
* * * Physical activity can promote physical adaptation to loading,
and restore and maintain functional capacity. This may explain why
there is some evidence of the benefits of exercise for spinal
disorders. [32-241-30-20]
However, comparisons of workers with young and highly skilled
athletes is not appropriate. This is pointed out by the ISSLS text on
the Lumbar Spine (Wiesel et al.1996; Ex. 26-1620). The following quote
is from the chapter on biomechanics:
Comparison of athletic exercises with industrial labor is
complicated because, in the athletic field, (1) one deals with
young, healthy subjects; (2) there is a selection of individuals for
the specific tasks; (3) the specific task is always accompanied by
remedial exercises. In industrial labor, one is dealing with the
average population. There is almost no selection of the individuals,
and there are many monotonous tasks that are not interrupted by
remedial exercise. [Ex. 26-1620]
Dr. Michael Vender explained his belief that soft tissue has almost
limitless capacity to recover from injury.
We cannot explain the natural process of aging and gradual
deterioration of all body parts by the concept of cumulative trauma.
The most basic flaw in this logic revolves around the comparison of
the human body to a piece of metal [as reflected in the
biomechanical model espoused by ergonomists). [Unlike metal], the
body, when stressed or even injured, has the ability to heal and
recover.--When one repeatedly bends a piece of plastic, it becomes
permanently deformed. When one repeatedly exercises a muscle, it
becomes stronger and more functional. [Ex. 32-241-3-19]
This belief is in contrast to the opinion of the NAS workshop
(1999) (Ex. 26-37) noted above, and fails to recognize concepts of
muscle disruption, tendon and ligament viscoelastic deformation and
creep discussed in the Health Effects Preamble.
7. Additional Criticisms of Epidemiological Studies Raised by
Commenters
Gibson, Dunn & Crutcher in their post-hearing comments (Ex. 500-
118, Section B, pgs. 65-81) supply critiques of additional ``studies on
which OSHA relies or may rely in support of the proposed rule.'' (id.,
pg. 65). OSHA's response to these critiques is given below.
Gibson Dunn & Crutcher criticize the study by Latza et al. (2000,
Ex. 38-424) that examined occupational risk factors of low back pain
among construction workers. Among their criticisms, Gibson Dunn &
Crutcher argue that the authors drew causal inferences from a study
that is only an exploratory analysis. Further, they claim that the
researchers were vague in their methods and did not come up with a
single promising association.
OSHA disagrees with these criticisms. First, the study as a whole
cannot be
[[Page 68537]]
fairly characterized as an ``exploratory analysis.'' This study is an
adequately designed longitudinal epidemiological study where
construction workers who reported no low back pain at baseline were
followed for three years. The ``exploratory approach'' reported by the
authors refers not to the study as a whole but rather to a detailed
analysis of the data to identify potential risk factors that might be
used to predict low back pain. The authors describe a detailed process
for focusing on factors most likely to have caused the observed reports
of low back pain. Second, OSHA disagrees that the authors were vague in
their methods. Various aspects of the study, such as the selection of
study subjects, data collection, and data analysis, were described in
clear enough detail that would allow the reader to assess the results
reported. Finally, the authors noted that causality cannot be
established with this study. However, the purpose of the study was to
identify possible risk factors for low back pain among these workers
that might aid in the identification of hazardous components in the
work that can guide effective primary intervention. In this regard, the
authors report positive associations that show that certain
occupational risk factors can be predictive of low back pain.
Gibson, Dunn & Crutcher criticize a study by Punnett et al. ``A
comparison of Approaches to Modeling the Relationship between Ergonomic
Exposures and Upper Extremity Disorders'' (2000, Ex. 500-71-43). This
is a methodology study concerning approaches for combining independent
and dependent variables for the purpose of exposure-response analysis.
This study uses the information on upper extremity disorders in vehicle
manufacturing found in an earlier Punnett et al. (1998, Ex. 26-38)
study), which these same commenters criticized previously (Ex. 32-241-
4, pg. 144). OSHA has responded to those criticisms elsewhere in this
preamble.
Gibson, Dunn & Crutcher have two main criticisms of the Kurppa et
al., (1991, Ex. 26-53) study concerning the incidence of tenosynovitis
or peritendinitis and epicondylitis in a meat-processing factory. The
commenters claim that the diagnostic definition of the response
tenosynovitis or peritendinitis (agreed to by the plant physician),
``boils down to focal soreness/tenderness and nothing more specific or
mysterious than that.'' (Ex. 500-118, pg. 71). In response, OSHA notes
that, in order to be included as a response in the study, the condition
needed to be severe enough in each case to qualify for sick leave (Ex.
26-53, pg. 33). As a result, OSHA believes that the response is a
meaningful health effect, i.e., because it was serious enough to
warrant time away from work for recuperation. Gibson, Dunn & Crutcher
(Ex. 500-118 pg 71) also claim that, ``By its very nature, a
surveillance study perturbs the experience of discomfort.'' However,
this type of physiological biasing factor would appear to have only a
minimal or no effect on the end results since the rate of occurrence of
tenosynovitis or peritendinitis and epicondylitis, for both men and
women, was shown typically to be an order of magnitude higher for
strenuous compared to non-strenuous meat processing jobs (Ex. 26-53,
pg. 34).
Gibson Dunn & Crutcher correctly point out (Ex. 500-118, pg. 72-73)
that the utility of participatory ergonomics was not evaluated in the
Roquelaure et al. (1997, Ex. 38-96) study. However, OSHA used this
study only to show an association between stress variables and carpal
tunnel syndrome (CTS). The role of participatory ergonomics in reducing
CTS was not alluded to by OSHA.
Gibson Dunn & Crutcher correctly point out (Ex. 500-118, pg. 73)
that in the Viikari-Juntura et al. (1994, Ex. 26-873) study what is
defined as severity of neck trouble is in fact the frequency of self-
reported symptoms (pain, ache, stiffness or numbness). As a result,
Gibson Dunn & Crutcher believe the possibility exists that the
subject's statements concerning severe neck trouble could be
misleading. OSHA used the Viikari-Juntura et al. study to only show an
association between neck symptoms and stress factors. OSHA did not
comment on the severity of the symptoms.
Gibson Dunn & Crutcher note (Ex. 500-118, pgs. 73-74) that the
authors of the Kearns et al. (2000, Ex. 500-71-34) study did not intend
that the results of the study on the prolongation of median motor and
sensory nerve latency be generalized beyond the effects of work related
to pork processing. OSHA agrees that the study supplies limited
information about the relationship between workplace physical factors
and CTS.
Stenlund et al.studies, Exs. 26-733 and 26-1479
Gibson Dunn & Crutcher (Ex. 500-118 pg. 70-71) have criticized the
1992 study by Stenlund et al. (Ex. 26-733) of osteoarthrosis and the
1993 Stenlund et al. (Ex. 26-1459) of shoulder tendinitis. First, the
1992 Stenlund et al. study is criticized for its conclusion that
radiographic evidence of osteophytes (spurs) in the acromioclavicular
joint is a predictor of osteoarthrosis causing cartilage loss and
abnormal reparative processes. Gibson Dunn & Crutcher argue that in
other joints, such as the knee, increased usage leads to osteophytosis
(spurs) and increased preservation of cartilage, which is good. They
question whether the Stenlund et al. (1992) paper is detecting a
``bad'' outcome. Gibson Dunn & Crutcher also criticize the 1993
Stenlund et al. paper for using shoulder tendinitis as an adverse
effect measure, arguing that shoulder tendinitis is subject to overt
reporting and recording bias. They conclude that these types of outcome
measures are not appropriate to be used in epidemiological studies.
With regard to the 1992 Stenlund et al. study, the critics are
comparing minimal changes commonly observed with habitual usage of a
joint such as the knee (e.g., increased preservation of cartilage) to
severe osteoarthrosis, from heavy manual work and vibration, of a
joint, in this case the shoulder. In the Stenlund study, radiographs
were classified into 5 grades of osteoarthrosis (0 = normal; 1= minimal
changes; 2 = moderate changes, more severe changes to cartilage and
bone structure begins to be affected; 3 = severe osteoarthrosis, and 4
= totally destroyed joint). Those classifying the radiographs were
blinded as to exposure. The authors did not find significant
differences in lower grade changes. However, they did observe that
among rock blasters and bricklayers who had exposure to heavy load and
vibration compared to foremen who did not, there was a significant
increase in grade 2 and 3 osteoarthrosis. Therefore, OSHA believes that
Gibson Dunn & Crutcher are actually confusing two different health
outcomes in their criticism. The study by Stenlund et al. (1992) would
support the hypothesis that normal habitual use of the shoulder might
cause increased preservation of the cartilage. However, shoulder joints
exposed to heavy loads and vibrations such as those examined in the
study show radiographic evidence of severe osteoarthrosis.
With regard to the 1993 Stenlund et al. study, the authors noted
the potential for misclassification when using tendinitis as a measure
of outcome. They agree that in some epidemiological studies, clinical
diagnosis of tendinitis may not be an appropriate measure of prevalence
in the population, since some individuals with tendinitis may not see a
physician for their symptoms, thus creating a selection bias. However,
the authors assert that this type of bias is overcome in their study by
the use of a cross sectional study design. In order to further lessen
the potential for misclassification, the authors also
[[Page 68538]]
included symptoms of pain during the last year that could have
originated from structures other than the tendons or muscle attachment
inflamation in addition to using palpation and isometric contraction.
They reasoned that persons experiencing pain in their shoulder in the
last year and who on examination have pronounced pain reaction to
palpation and contraction, have probably had a disorder in the muscle
attachment or tendon, that in clinical practice would have been
classified as tendinitis. OSHA believes that, with proper study design
and control for misclassification, as was done in the Stenlund study,
clinically diagnosed shoulder tendinitis is an adequate measure of
effect. Thus, the Stenlund et al., 1993 study can be used with other
studies in the record to form a reliable weight of evidence on which to
base the agency's health effects conclusions.
Gibson Dunn & Crutcher also criticized the 1990 study on
degenerative disc disease among concrete workers and house painters by
Riihimaki et al. (Ex. 502-455). They argue that the results of this
study are ``not compelling'' because the authors found insignificant
risk ratios and, thus, are very likely to be influenced by unmeasured
variables. OSHA finds this argument unconvincing for the following
reasons. Number one, the authors did, in fact, find a statistically
significant risk of detectable degenerative changes in the lumbar spine
among concrete workers (38%) compared to house painters (26%).
(Relative Risk=1.4, (CI 1.1-1.8; p0.01)) In this study, concrete
reinforcement workers were compared to house painters. The authors
noted that the load on the back is distinctly different among concrete
workers compared to house painters. The authors also note that in
Finland, persons in these trades have very similar socio-economic
status and lifestyles, thus making it more likely that the detected
difference between these groups is due to occupational exposures rather
than other factors. Moreover, as a part of the study design the
concrete reinforcement workers and house painters were matched by age,
earlier back accidents, height, body mass index and smoking. These
covariates were included in a mutivariate logistic regression to
perform the statistical analysis to control for possible confounding
factors likely to affect disc degeneration. After controlling for these
factors, the authors still reported statistically significant effects.
In addition, the authors noted that workers, to be included in the
study, had to have at least 5 years seniority, thus creating the
possibility for negative bias due to health-based self-selection of
workers in the more physically demanding job (i.e. concrete workers).
The effect of this negative bias, however, would underestimate the risk
ratios. In an attempt to understand the underlying etiology of this
disc degeneration, the authors did additional analyses looking at
different segments of the lumbar region and different degenerative
spinal changes (e.g. disc space narrowing, spondylophytes, and endplate
sclerosis). In some of these sub-analyses for certain lumbar regions,
there was no statistically significant effect. Overall, however, the
authors found a significant association between work and disc
degeneration while controlling for confounders. Therefore, OSHA does
find these results compelling and generally supportive of its health
effects assessment.
Gibson Dunn & Crutcher criticized the 1994 study of sciatic pain
among men in machine operating, dynamic physical work and sedentary
work by Riihimaki et al. (1994, Ex. 26-1188). They claim that the
associations observed in this study are ``barely significant'' (Ex.
500-197, pg. 69) and are no more significant than the associations
observed with physical exercise. In addition, they state that the
observed increases are negatively influenced by workers' self reporting
of tasks, ``an inadequate definition of sciatica'' and recall bias.
OSHA is unsure as to what these critics mean by ``barely''
significant. The authors reported a statistically significant increase
in sciatic pain among machine operators and carpenters compared to
office workers. For machine operators the relative risk =1.6 (95% CI
1.2-2.2) and for carpenters was 1.7 (95% CI 1.3-2.4). This statistical
significance remained even after controlling for a variety of risk
factors (e.g., age, seniority, education, physical exercise, smoking,
car driving, and prior back accidents). Adjusted relative risks were
1.4 and 1.5.
The authors do acknowledge that the reporting of symptoms of
sciatica can be subjective, as can a worker's perception of physical
task. In order to minimize this type of bias, they used explicit
descriptions of symptoms and tasks to ensure uniform understanding of
the concepts. The authors also recognize the potential of recall bias
to negatively influence the results. However, they note that this
misclassification also depends not only on the recall error but also
the incidence rate of the symptoms. They conclude that the recall error
bias in the observed risk ratios is small if ``by the end of follow-
up'' the rate of reporting symptoms among the misclassified subjects
does not deviate much from the overall incidence rate. Thus, while OSHA
acknowledges the potential bias pointed out by the critics of this
study, the agency believes that these sources of bias have been taken
into consideration in this study to such an extent that the observed
increased risk ratios can be accepted with some confidence. In
addition, OSHA believes that these observed risk ratios are more than
barely significant and, when viewed in the context of other positive
epidemiological evidence, contribute to the weight of evidence and the
strength of the agency's overall health effects assessment.
Gibson Dunn & Crutcher also criticize four other epidemiology
studies OSHA relied on in contributing to the strength of the agency's
overall health effects assessment: two studies by Silverstein et al.
(Exs. 26-34 and 26-1404), a study by Venning et al. (Ex. 500-41-49),
and a study by Punnett et al. (Ex. 26-39). OSHA responds to criticisms
of these 4 studies in on Section G:3-Exposure-Response.
VI. Risk Assessment
A. Introduction
The United States Supreme Court, in the Benzene decision
(Industrial Union Department, AFL-CIO v. American Petroleum Institute,
448 U.S. 607 (1980)), has ruled that the OSH Act requires, prior to the
issuance of a new standard, that a determination be made that there
exists a significant risk of material impairment and that issuance of
the new standard will substantially reduce that risk. The Court stated
that ``before he can promulgate any permanent health or safety
standard, the Secretary is required to make a threshold finding that a
place of employment is unsafe in the sense that significant risks are
present and can be eliminated or lessened by a change in practices''
(448 U.S. 642). The Court also stated that ``the Act does limit the
Secretary's power to require the elimination of significant risks''
(448 U.S. 644).
In the Cotton Dust case (American Textile Manufacturers Institute
v. Donovan, 452 U.S. 490 (1981)), the Court reaffirmed the position it
had previously taken in the Benzene decision that a risk assessment is
not only appropriate but required to identify significant health risks
in workers and to determine if a new standard will reduce those risks.
Although the Court did not require OSHA to perform a quantitative risk
assessment in every case, the Court implied, and OSHA as
[[Page 68539]]
a matter of policy agrees, that assessments should be put into
quantitative terms to the extent possible.
The weight of evidence presented in the Health Effects section of
this preamble (Section V) demonstrates a causal relationship between
exposure to workplace risk factors and work-related musculoskeletal
disorders. As discussed in that section, the major workplace risk
factors include exposure to repetitive motion, force, awkward postures,
contact stress, and segmental vibration. The Health Effects section
also demonstrates that the risk associated with occupational exposure
to these risk factors increases with frequent or prolonged exposure to
these risk factors, and that the risk is increased when workers are
exposed to more than one risk factor in a job.
OSHA has determined that there is substantial evidence that
exposure to these biomechanical stressors at work can cause or
contribute to the development of MSDs and that reductions in these
stressors can reduce the number and severity of these work-related
MSDs. The underlying evidence falls into three broad categories:
Studies of groups of workers showing a relationship between
exposure to biomechanical risk factors in the workplace and an
increased incidence or prevalence of MSDs;
Biomechanical studies that show that adverse tissue reactions
and damage can occur when tissues are subjected to high forces and/
or a high number of repetitive movements, which occur when workers
are substantially exposed to biomechanical risk factors; and
Scientific and case studies that demonstrate that workplace
interventions designed to reduce exposures to biomechanical risk
factors are effective in reducing the internal forces imposed upon
tissues and the incidence and severity of MSDs.
In the Health Effects section of this preamble, OSHA summarizes
data and findings from more than 170 epidemiological studies of the
incidence or prevalence of MSDs in groups of workers who are exposed to
physical risk factors in their jobs. In most of these studies, the MSD
prevalence of a group of exposed workers is compared to that in another
worker group that is not exposed to the risk factors of interest. If
the exposed group shows a higher MSD prevalence than does the reference
group, the study provides evidence of an association between exposure
and an increased risk of developing MSDs, particularly if the study is
of good quality and adequately controlled for potentially confounding
factors (such as age and gender) and biases.
Many of these epidemiological studies were reviewed by the National
Institute for Occupational Safety and Health (NIOSH) in 1997 (Ex. 26-1)
to evaluate the strength of the evidence for a causal relationship
between several types of MSDs and the workplace risk factors of force,
repetitive motion, awkward posture, and vibration. More than 600 peer-
reviewed studies were critically reviewed, making this one of the
largest human data bases ever built to examine work-related adverse
health outcomes. NIOSH found that for most combinations of MSDs and
risk factors, the evidence in humans that a causal relationship existed
between workplace exposure to risk factors and the development of MSDs
was either ``sufficient'' or ``strong.'' For a few MSD/risk factor
combinations, there was insufficient evidence of a causal relationship,
but in no case did NIOSH determine that there was evidence for the
absence of a relationship between exposure to workplace risk factors
and the development of MSDs. NIOSH concluded that `` * * * a
substantial body of credible epidemiologic research provides strong
evidence of an association between MSDs and certain work-related
physical factors when there are high levels of exposure and especially
in combination with exposure to more than one physical factor * * *''
(NIOSH 1997, ES p. xiv, Ex. 26-1).
A similar conclusion was reached by the experts participating in a
workshop conducted by the National Academy of Sciences/National
Research Council (NRC) (Ex. 26-37). For the NRC report, a panel of
experts critically reviewed the methods used to select and evaluate the
human studies relied on in the 1997 NIOSH study (Ex. 26-1). The 1999
NRC report concluded as follows:
[the association between MSDs and exposure to risk factors at work
that have been] identified by the NIOSH review * * * as having
strong evidence are well supported by competent research on heavily
exposed populations.
There is a higher incidence of reported pain, injury, loss of
work, and disability among individuals who are employed in
occupations where there is a high level of exposure to physical
loading than for those employed in occupations with lower levels of
exposure. (Ex. 26-37)
In this context, NAS's use of the phrases ``heavily exposed'' and
``high level of exposure'' does not refer to any specific
quantitatively defined level of exposure to biomechanical risk factors,
but simply reflects that, in the epidemiological studies, groups of
workers who were considered to be ``exposed'' to biomechanical risk
factors experienced higher intensities and durations of exposure than
did the comparison, or referent, groups of workers. In general, workers
in the exposed groups were exposed to biomechanical risk factors on a
nearly daily basis, and were usually exposed for most of each work
shift. However, as shown by OSHA's summary of exposure-response data in
the Health Effects section (Section V), many of these epidemiological
studies placed workers in the exposed group even if they were exposed
for only about one-quarter to one-half of the work shift. Later in this
section, OSHA defines ``higher-risk'' workers as those who are exposed
in excess of the final rule's job screening criteria, which generally
reflects those workers as having two or more hours per shift of
exposure to biomechanical risk factors.
Since the NIOSH and NAS reports, many additional epidemiological
studies have been published and are contained in the rulemaking record.
These studies have been reviewed by OSHA in detail in the Health
Effects section, and their results add to the already substantial
weight of evidence originally evaluated by NIOSH and NAS. OSHA is not
alone in its determination that the epidemiological data base for
ergonomics convincingly establishes a causal relationship between
workplace exposure to risk factors and MSDs. Many experts who provided
testimony in the record and appeared at OSHA's informal hearing agreed
that sufficient epidemiological evidence exists to conclude that
biomechanical factors at work cause or contribute to MSDs. These
experts included researchers, medical professionals, and ergonomists
(Exs. 37-1, 37-2, 37-9, 37-10, 37-13, 37-10, 37-15, 37-16, 37-17, 37-
18, 37-21, 37-27; Tr. 843, Tr. 1048; Tr. 1112, Tr. 1103-1103, Tr. 1367,
Tr. 9808-9809, Tr. 16802, Tr. 17566-17567, Tr. 8261, Tr. 2834, Tr.
9297, Tr. 16145, Tr. 1959-1960, Tr. 17358, Tr. 13330-13331, Tr. 3412).
That exposure to workplace risk factors can cause or contribute to
MSDs is made more plausible by the growing body of studies of
biomechanical effects, also summarized in the Health Effects section
(Section V of this preamble), that are designed to explore how tissues
react to mechanical stress and how those reactions are related to
disease processes. OSHA presented detailed scientific information on
the biomechanics and pathophysiology of MSDs in its Health Effects
Appendicies, prepared at the time of the proposed rule (Ex. 27-1); the
discussion below briefly summarizes the information
[[Page 68540]]
reviewed in the Health Effects Appendicies and in the Health Effects
section.
Although all soft musculoskeletal tissue can tolerate certain
physical loads, these tissues will respond adversely if the load
becomes excessive. Muscles, ligaments, tendons, and tendon sheaths can
become inflamed with repetitive or prolonged loading, cartilage can
deteriorate when subjected to abnormal loads, and nerves can exhibit
dysfunction and eventually permanent damage if compressed or subjected
to extended tension. Other studies have shown that the kinds of risk
factors present in many industrial occupations can impose internal
forces on soft musculoskeletal tissue sufficient to cause the kinds of
physiologic responses described above. The relationships between
external and internal loads have been demonstrated using both
biomechanical models and direct measurement and observation in the
workplace (see Section V, Health Effects).
Finally, evidence of the work-relatedness of MSDs comes from
several studies and case reports that document the effectiveness of
ergonomic interventions in reducing exposures to risk factors and the
successes of individual companies' ergonomics programs in reducing the
incidence or prevalence of MSDs and the severity of MSDs among their
workers. After reviewing intervention studies, including both field and
laboratory studies, the NRC (1998, Ex. 26-37) concluded that
* * * specific interventions can reduce the reported rate of
musculoskeletal disorders for workers who perform high-risk tasks.
No known single intervention is universally effective. Successful
interventions require attention to individual, organizational, and
job characteristics, tailoring the corrective action to those
characteristics.
The scientific evidence and case studies demonstrating that ergonomic
interventions reduce excessive tissue loads and the associated tissue
pathology, and reduce MSD incidence and severity, are summarized later
in this section).
In addition to biomechanical risk factors present at work, the risk
of developing an MSD is also influenced by individual, organizational,
and social factors. Factors that affect individual susceptibility
include age, general conditioning, and pre existing medical conditions.
Although some of these individual factors have been identified in human
studies as being statistically significant predictors of disease, they
are generally much weaker predictors than are biomechanical factors of
force, repetition, posture, and vibration (NRC 1998, Ex. 26-37).
Organizational factors that have been linked to MSDs include poor job
content (e.g., lack of job variety) and job demands (e.g., excessive or
highly variable workload and time pressure). The importance of poor job
content is difficult to evaluate, since this factor can coexist with
biomechanical factors (for example, excessive workload can result in a
worker needing to increase repetitive movement and/or force). Social
factors refer to a lack of social support from management and
supervisors, which can lead to psychological stress and dissatisfaction
with work, both associated with an increased prevalence of MSDs.
However, after evaluating the nature of psychosocial factors and their
role in contributing to the risk of MSDs, OSHA has determined that,
although psychosocial factors appear, at least in some studies, to have
some relationship to the observed increases in the incidence of MSDs
among workers exposed to risk factors, their effect is independent of
that of biomechanical factors and is generally not as predictive of MSD
risk as are biomechanical factors. The evidence reviewed by the Agency
suggests that psychosocial factors may have a greater influence in
determining the length of disability following development of an MSD
than do biomechanical factors, but have shown weaker associations with
the prevalence or incidence of MSDs than have biomechanical factors
(see Section V.G.5 of the Health Effects Section for a discussion of
the literature dealing with psychosocial effects). OSHA's finding is in
accord with that of the NAS review (1999, Ex. 26-37).
OSHA believes that the human epidemiologic studies, the
biomechanical and physiological studies, and the studies of the
effectiveness of workplace ergonomic interventions together constitute
a compelling body of evidence that demonstrates that exposure to risk
factors at work is a major factor in the development of MSDs, and that
reducing or eliminating exposures to these risk factors will reduce the
number and severity of these MSDs.
The epidemiological data base that describes the associations
between exposure to workplace risk factors and increased prevalence or
incidence of MSDs is vast. The nature of the hazard and of the
available data require OSHA to perform a different type of risk
assessment than it performs to assess occupational risks from chemical
exposures. There are many reasons for this, in particular the complex
interactions among different kinds of exposures that lead to tissue
injury and disorders and the difficulty of defining exposure metrics
that reflect all of the various combinations of risk factors to which
workers are exposed across industry. This is not to say that exposure-
response relationships have not been observed or cannot be defined in
specific circumstances; in fact, there are many cases in which the risk
of MSDs has been quantitatively related to the degree and intensity of
exposure. In the Health Effects section of this preamble (Section V),
OSHA describes scientific studies that demonstrate a positive
association between the magnitude and/or duration of exposure to
workplace risk factors and the prevalence of MSDs, including upper
extremity disorders and back injuries. OSHA concludes that these
studies provide compelling evidence of the work-relatedness of MSDs,
since a finding of positive exposure-response trends is one of the key
findings necessary to establish a causal relationship between exposure
and disease.
Using data on the incidence of work-related MSDs, risk can be
quantified using a population-based approach similar to the one used by
OSHA to quantify the risk of Hepatitis B among workers with frequent
occupational exposure to blood and other potentially infectious
material (56 FR 64004). For this final ergonomics program rule, OSHA
uses a similar approach in its final risk assessment. In this
assessment, OSHA relies on data from the Bureau of Labor Statistics
(BLS) to estimate the annual incidence of work-related MSDs in
different industry sectors and occupations, by type of injury and type
of exposure. A description of these data and OSHA's analytical approach
are described in part B below, and the results of this analysis appear
in part C.
Having quantified the risk, it is important to determine the extent
to which the standard is likely to reduce that risk. In the case of
this ergonomics program standard there is abundant evidence of the
effectiveness of ergonomic programs. This evidence comes from a variety
of published studies, articles, and unpublished data that describe the
reductions in risk ergonomics programs have actually achieved in the
workplace. Most commonly, this evidence is expressed in terms of
reductions in injury rates and decreases in the numbers of lost
workdays caused by MSDs. OSHA's discussion of these data appears in
part D, below. The Agency presents the results of its risk analysis in
parts C and D; comments on the preliminary risk
[[Page 68541]]
assessment (64 FR 65926) follow these sections.
B. Data Sources and Analytical Approach
The annual Survey of Occupational Injuries and Illnesses conducted
by the Bureau of Labor Statistics (BLS) is the principal data source
for evaluating the risks to employees of developing a work-related
musculoskeletal disorder. This survey is conducted under a joint
federal/state program that collects workplace injury and illness data
from about 165,000 private industry establishments. The survey requests
information only on non-fatal injuries and illnesses, and excludes the
self-employed, farms with fewer than 11 employees, private households,
and employees in federal, state, and local government agencies.
For this survey, selected employers are required to provide
statistics on the total number of injuries and illnesses recorded on
the OSHA Form 200 (the ``OSHA Log''), as well as information describing
the nature and causes of their lost workday injuries and illnesses.
Thus, according to the BLS, the data provided by employers ``* * *
reflect not only the year's injury and illness experience, but also the
employer's understanding of which cases are work-related under current
record keeping guidelines of the U.S. Department of Labor.''
Information from employers is provided in sufficient detail to permit
the BLS to systematically code each reported case and develop estimates
of the numbers and incidence of each specific type of LWD injury and
illness for the United States as a whole, by industry sector and by
occupation.
Although the BLS data are the best available data on the number and
kinds of job-related injuries and illnesses occurring among U.S.
workers in any given year, there is no single BLS-reported number that
represents all employer-reported musculoskeletal injuries and illnesses
occurring in that year. Instead, employer-reported injuries and
illnesses are coded by the BLS according to a classification system
that categorizes each incident by type of injury or illness and by
nature of the exposure event leading to the injury or illness (Ex. 26-
1372). The types of disorders that are addressed by the standard fall
into several of these BLS injury and illness categories.
To use these data, OSHA identified the kinds of cause-specific
injuries and illnesses, as coded by the BLS, that reflect MSDs of the
kinds that will be covered by the ergonomics program standard. An OSHA
panel, which included an occupational physician and two professional
ergonomists, examined the BLS listing of occupational injury and
exposure event codes and their definitions from the manual provided to
state personnel who code the data from the BLS employer survey. The
table contained in Appendix VI-A at the end of this Risk Assessment
section provides the list of injury categories that were initially
selected by this panel as being likely to include at least some work-
related MSDs. From this initial list, the panel selected a subset of
injury categories that predominately included work-related MSDs of the
type that has been associated with exposure to the biomechanical risk
factors addressed by the final rule; these categories appear in Table
VI-1. Of the injury categories selected, OSHA chose to base its
analysis exclusively on six injury categories that were deemed by these
experts to be most relevant and most likely to represent a large
proportion of lost workday MSDs; in other words, OSHA deliberately
excluded several categories such as ``traumatic injuries to bones,
nerves, and spinal cord,'' ``symptoms involving nervous and
musculoskeletal systems, unspecified,'' and ``disorders of the
peripheral nervous system, unspecified.'' The injury categories
included by OSHA for the risk assessment were:
Sprains, Strains, and Tears;
Back Pain, Hurt Back;
Soreness, Hurt, except back;
Carpal tunnel syndrome;
Hernia; and
Musculoskeletal and connective systems diseases and disorders.
[[Page 68542]]
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[[Page 68543]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.001
For this analysis, OSHA is interested in capturing only those
injuries and illnesses that are associated with exposure to the risk
factors addressed in the final rule. These risk factors are repetitive
motion, excessive force,
[[Page 68544]]
awkward postures, contact stress, and segmental vibration. The annual
BLS survey does not break out the causes of injuries and illnesses
captured by the survey in a manner that precisely matches the kinds of
risk factor exposures covered by the rule. However, the OSHA panel did
identify the three exposure event categories defined by the BLS that
are the most closely related to these risk factors. These are:
``Repetitive motion,'' which reflects the risk factors of
repetitive motion, sometimes combined with force and/or awkward
posture, and contact stress, which is a combination of repetitive
motion and force;
``Overexertion,'' which includes activities such as
lifting/lowering, pushing/pulling, holding/carrying, and throwing, and
thus reflects the risk factor of force, sometimes combined with
repetitive motion and/or awkward posture; and
A subcategory of ``bodily reaction'' that includes
``bending, climbing, crawling, reaching, twisting,'' which reflects the
risk factor of awkward posture.
The BLS definitions for these exposure event categories appear in
Table VI-2. Note that musculoskeletal injuries and illnesses caused by
acute events such as slips, trips, falls, being struck by objects, or
by motor vehicle accidents are excluded from the data relied on in
OSHA's risk analysis (because they are not included in the coverage of
the final rule (see paragraph (a) of the regulatory text)). The process
used by OSHA to identify those injury and exposure event categories
from which to select the BLS data represents the closest approximation
possible from the data available to OSHA of the MSDs that the final
rule will actually cover.
The BLS injury and illness coding system also includes two exposure
event categories that reflect exposure to vibration involving damage to
the nerves or circulatory system (Ex. 26-1372). They include:
Event code 05, rubbed or abraded by friction or pressure;
this code includes injuries caused by rubbing or abrasion by ``objects
being handled,'' and includes ``superficial injuries such as blisters,
scratches, or abrasions,'' as well as those involving nerve or
circulatory damage, and
Event code 06, rubbed, abraded, or jarred by vibration,
which includes injuries caused by vibration of mobile equipment or
vehicles, as well as other machines or equipment.
[[Page 68545]]
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[[Page 68546]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.003
MSDs caused by segmental vibration are thus included with those
caused by whole-body vibration in both event categories, which makes it
difficult to separate out those vibration-induced injuries and
illnesses related only to
[[Page 68547]]
segmental vibration, one of the risk factors covered by the standard.
The BLS estimated that a total of 5,465 injuries related to exposure
events classified under these two categories (excluding injuries
involving the eyes) had occurred in 1996 (see BLS Table R32 for 1996,
available at http://www.bls.gov/oshc_d96.htm). Because it is not
possible to identify the number of injuries associated with segmental
vibration, OSHA has included in its analysis only those MSDs related to
the three event codes of overexertion, repetitive motion, and the
subcategory of bodily reaction described above. The injury/illness and
event codes used by OSHA in the Risk Assessment and Significance of
Risk sections for the final rule are the same as those used to support
these analyses of the proposed rule. OSHA's decision not to include
vibration-induced injuries and illnesses in the universe of MSDs means
that the risks estimated in the final Risk Assessment section, and the
estimates in the Significance of Risk section, are understated.
OSHA received numerous comments on its selection of injury/illness
and exposure event codes from those used in the BLS classification
system. In particular, several commenters objected to OSHA's inclusion
of injuries categorized as ``strains, sprains, and tears,'' because, in
their view, such injuries reflect acute injury events, while OSHA's
ergonomics program standard was intended to address injuries that arise
from cumulative damage through long-term exposure to risk factors.
These commenters include, among others, the Chamber of Commerce (Ex.
30-1722), the American Iron and Steel Institute (Exs. 30-3951, 32-206),
Gibson, Dunn, & Crutcher on behalf of numerous clients (Exs. 500-197,
32-241), the National Coalition on Ergonomics (Ex. 32-368), the
American Forest & Paper Association (Ex. 30-3865), the AEI-Brookings
Joint Center (Ex. 30-3911), Edison Electric Institute (Ex. 32-300-1),
the Center for Office Technology (Ex. 30-2208), Integrated Waste
Services Association (Ex. 30-3853), Organization Resources Counselors
(Ex. 30-3813), the American Meat Institute (Ex. 30-3677), Guilford
Mills (Tr. pp. 11519-11520, 11566-11567), the Puerto Rico Manufacturers
Association (Ex. 30-3348), and the National Paint and Coatings
Association (Ex. 30-4340). In support of their views, these commenters
point to the BLS's definition of ``strains, sprains, and tears,'' which
appeared on Table VI-1 of the preamble to the proposal (64 FR 65928--
65929) and reads as follows:
This nature group classifies cases of sprains and strains of
muscles, joints, tendons, and ligaments. Diseases or disorders
affecting the musculoskeletal system, including tendinitis and
bursitis, which generally occur over time as a result of repetitive
activity should be coded in Musculoskeletal System and Connective
Tissue Diseases and Disorders, major group 17. (Ex. 26-1372)
Based on this definition, Gibson, Dunn, & Crutcher conclude that cases
classified as sprains, strains, and tears represent single-incident
traumatic injuries and ``are not MSDs'' (Ex. 500-197, p. I-166).
To further support their view that strains, sprains, and tears
reflect acute injury events and not cumulative trauma, Gibson, Dunn, &
Crutcher note that most of the strain, sprain, and tear injuries
described in OSHA's preliminary risk assessment were associated with
overexertion, which is defined by the BLS as follows:
Overexertion applies to cases, usually non-impact, in which the
injury or illness resulted from excessive physical effort directed
at an outside source of injury or illness * * * Free bodily motions
that do not involve an outside source of injury or illness are
classified either in major group 21, Bodily Reaction, or in major
group 23, Repetitive Motion. (Ex. 26-1372)
Thus, Gibson, Dunn, and Crutcher argue that
Clearly, nothing in this definition suggests that overexertion
injuries develop gradually over time. To the contrary, this
definition expressly excludes injuries that result from repetitive
motion. There is simply no evidence that sprains, strains, and tears
associated with overexertion meet the definition of an MSD. (Ex.
500-197, p. I-167)
Similarly, the Chamber of Commerce stated: ``It is not difficult to
imagine that many, if not most of these injuries * * * may well have
occurred as the result of a single instantaneous event.'' (Ex. 30-1722)
Gibson, Dunn & Crutcher (Ex. 500-197), AISI (Exs. 32-206, 30-3951),
the American Forest & Paper Association (Ex. 30-3865), the American
Meat Institute (Ex. 30-3677), and the Hon. David M. McIntosh of the
U.S. House of Representatives (Ex. 30-542) all objected to the
inclusion of cases from BLS category 0972 (back pain, hurt back) in the
universe of MSDs on the grounds that these are traumatic injuries as
well. To support this position, Gibson, Dunn, & Crutcher pointed to
OSHA's Record Keeping Guidelines for Occupational Illnesses and
Injuries, commonly known as the ``Blue Book.'' These guidelines
instruct employers how to record occupational injuries and illnesses on
their OSHA 200 logs. Gibson, Dunn & Crutcher argued that, in the Blue
Book, OSHA ``concedes'' that back cases should be categorized as
injuries rather than illnesses. According to Gibson, Dunn and Crutcher
(Ex. 500-197):
OSHA states that back cases are ``injuries'' that are ``usually
triggered by an instantaneous event'' for purposes of OSHA 200
recording, [but] converts them into ``illnesses'' that develop
``gradually over time'' for purposes of its MSD statistics * * * The
bottom line is that OSHA has no reliable data regarding the causes
of back pain and back injuries. OSHA allows employers to
``generalize'' about back pain for purposes of OSHA 200 recording
precisely because its causes are often indeterminate.
OSHA has carefully considered these comments and finds them
unpersuasive. It is necessary and appropriate to include these BLS
categories to arrive at an accurate estimate of the risk posed by the
biomechanical risk factors addressed in this standard.
First and foremost, OSHA is issuing its final ergonomics program
standard because of substantial evidence that workers who are regularly
exposed to biomechanical risk factors are at an increased risk of MSDs
and the pain and disabilities associated with them. Whether these
injuries and illnesses come about because of an acute event or because
of pathology that develops over a longer term is not germane to the
issue of whether workers who are regularly exposed need protection. The
sole consideration is that increased exposure to biomechanical risk
factors increases the risk to the worker. For example, a worker whose
job involves heavy lifting on a regular basis is at an elevated risk of
suffering a low back disorder. Such a disorder may arise either because
repeated lifting is causing cumulative wear resulting in degenerative
changes to the disc, or because the stress imposed on the spine during
lifting can overcome the capacity of the disc to withstand compression,
resulting in acute structural failure (see Section V.E on the health
evidence for low-back disorders). Although a worker who lifts heavy
loads infrequently may be at risk from acute failure, the worker who
lifts frequently as part of their regular job is at greater risk via
either mechanism.
Furthermore, there is substantial evidence in the record that many
of the injuries coded as strains, sprains, and tears in fact develop
gradually over time. Several commenters believed that it was
appropriate for OSHA to include statistics on strains, sprains, and
tears in its assessment of MSD risks. For example, the AFL-CIO, in
their post-hearing brief, stated that
[[Page 68548]]
The industry is just plain wrong on this point [that back
injuries are traumatic injuries]. The BLS survey is based on
employer reports of injuries. To simplify recording, OSHA recording
criteria specifically specify that back injuries, one major source
of MSDs, should be recorded as injuries, even if they result from
chronic exposure conditions. Disorders related to repeated trauma,
including carpal tunnel syndrome are to be recorded as illnesses. *
* * Thus, it is OSHA's recording criteria and BLSs coding rules and
definitions that result in many MSDs, particularly back injuries,
being classified as sprains, strains, and tears. This category
includes injuries that may result from a single exposure and those
that result from repeated activities. OSHA has limited the types of
strains, sprains, and tears that are covered [in its risk
assessment] to those * * * associated with] exposures that are
covered by the rule (e.g., overexertion, repetition). (Ex. 500-218,
p. 13-14)
Testimony from Dr. Frank Mirer of the United Auto Workers, who is also
a member of the BLS Labor Research Advisory Committee, explained why
MSDs of the back are frequently recorded as sprains and strains:
You have to understand the reality of this BLS database, which
is derived from [the] OSHA 101 form submitted by management medical
departments to OSHA or to the BLS. Now when a worker goes up to the
medical department * * * all they know is they hurt. And most of
them see a nurse and their disorder is just thrown into a bin. Back
conditions are all injuries. They come as strain and sprain * * *.
[W]e have acute flare ups, just as a back injury is a chronic
condition and has an acute flare up. So standard practice in the
industry * * * is [that] cases [considered to be] of ergo interest *
* * [include] sprain and strain injuries that are not accompanied by
a fall or some other traumatic [event] * * *. (Tr. 5896-5897)
When asked whether strains and sprains due to overexertion or
repetition were likely to be related to the risk factors covered by the
standard, both Dr. Rosecrance and Mr. Alexander agreed. Dr. Rosecrance
testified that injuries classified as sprains or strains are
appropriately considered MSDs, depending on the events leading to the
injury:
* * * I look at an MSD * * * as a disorder affecting muscles,
tendons, ligaments, bone, connective tissue. And certainly in my
definition of MSD, a sprain would meet that because a sprain is a
tear to a ligament * * * [It] perhaps [might] be a traumatic one or
from an acute injury like a slip or a trip * * *. When we review,
let's say, the OSHA 200 Log and there is a strain or sprain on
there, I will ask * * * what was the cause of that sprain or strain?
Was the strain from repetitive use or was it a strain from an acute
type of injury?
Some rulemaking participants provided evidence to the record
documenting that back disorders were frequently recorded as strains and
sprains without regard to the nature of the exposure or events
associated with each case. For example, the post-hearing submission of
the United Food and Commercial Workers Union (UFCW) (Ex. 500-133),
which contained copies of OSHA-200 logs (Ex. 500-133-2), reported
finding MSDs categorized as strains and sprains, back pain, hurt back,
carpal tunnel syndrome, hernia, and disorders associated with repeated
trauma. According to the UFCW, retail stores primarily categorized such
MSDs as sprains and strains, back pain and hurt backs, and injuries,
and seldom classified MSDs as illnesses. In contrast, the UFCW stated
that meatpacking industry logs more often accurately record MSDs as
illness, reflecting the greater experience this industry has in dealing
with ergonomic issues. A review of OSHA 200 logs submitted by the
Teamsters (Ex. 500-146) also shows that disorders that are clearly
recognized as MSDs, such as carpal tunnel syndrome and tendinitis, are
nevertheless often recorded by employers as injuries, which in turn
would be described in the BLS statistics as strains and sprains.
Other rulemaking participants described the use of sprain and
strain injury categories for ergonomic injuries in other injury
classification systems. In describing the province of Victoria's
(Australia) 1999 ergonomics regulation, which combined Victoria's
earlier manual handling and occupational overuse syndrome (OOS)
regulations, Mr. David C. Caple, Director, David Caple & Associates Pty
Ltd., testified that both repetitive injuries and back injuries were
combined under one generic sprain and strain category by that
regulation (Tr. 2723-2724). The Ford Motor Company's injury
classification system also combines strain and sprain injuries with
cumulative trauma disorders and other disorders of interest to the
company's ergonomics committee (Tr. 5826). When asked whether sprains
and strains are included within the category of repetitive motion
disorders under Oregon's workers' compensation law, Mr. Goodman replied
that they are often classified in that category, depending on the
events leading to the injury. He explained that Oregon's law defines an
injury as ``sudden and unexpected in onset'; thus, strains and sprains
would be considered repetitive motion disorders if the onset was slow
and insidious rather than sudden (Tr. 13694).
As described by the AFL-CIO submission and Dr. Frank Mirer's
testimony, all back disorders are classified as injuries rather than
illnesses, under OSHA's recordkeeping rules; as a result, back
disorders are commonly classified as strains and sprains, regardless of
whether the disorder arose from an acute, traumatic event or from
cumulative damage caused by prolonged exposure to risk factors.
Evidence in the record indicates that most cases of back pain arising
from exposure to risk factors of the type covered by the final rule do
not develop suddenly but are instead cases involving gradual onset,
which makes it difficult to identify or relate the back pain to a
single precipitating event. OSHA's witness, Dr. Stover Snook, testified
that
I am of the view and most scientists are of the view that that
is not typically how low back pain develops through traumatic things
like playing football on a weekend. It usually develops gradually
and insidiously, most of it, not all of it, but most of it does.
(Tr. 884)
In a study of back braces, Walsh and Schwartz (Ex. 30-3857-7) also
characterized the nature of work-related back disorders as being of
gradual onset:
Most back injuries are not the result of a single traumatic
incident but rather a compilation of minor traumatic events
occurring during normal working conditions for reasons that are
seldom obvious to the individual worker. Successive injuries result
in more severe impairment and increase the probability of long-term
disability * * *. In fact, improper body mechanics and unhealthy
work habits may take their toll on a daily basis. In recent years,
there has evolved a body of evidence that suggests that the etiology
of most but not all back pain is due to insidious and chronic
deterioration of the intervertebral disc, facet joints, and
ligaments in the back caused by biomechanical wear and tear. (Ex.
30-3857-7, p. 245)
OSHA's analysis of the biomechanical and pathological literature
dealing with work-related back pain leads to conclusions that are
consistent with these characterizations (see Section V, Health
Effects).
Because back disorders are recorded as injuries, notwithstanding
the mechanistic evidence described above that characterizes most back
disorders as being of chronic onset, practicing ergonomists believe
that it is important to investigate the underlying events associated
with recorded cases of strain or sprain to determine whether the injury
is related to excessive exposure to ergonomic risk factors. This
practice was described in the testimony of Dr. John Rosecrance,
Assistant Professor, University of Iowa and Mr. David Alexander,
President of Auburn
[[Page 68549]]
Engineers, Inc. and reflects an understanding that the classification
of back disorders as strains and sprains often does not mirror the true
nature of these disorders.
OSHA's final risk assessment (like its proposed assessment) relies
on statistics for strains and sprains that are associated only with
overexertion (i.e., lifting/lowering, pushing/pulling, holding/
carrying), repetitive motion, and bodily reaction (i.e., awkward
postures). Thus, OSHA's treatment of the BLS data exclude strains and
sprains that were determined by ergonomists or health care
professionals to arise from accidents, such as slips or falls. Based on
the evidence and testimony reviewed above, strains and sprain injuries
captured by the BLS system and classified under these three exposure
event codes properly reflect musculoskeletal disorders that arise as a
result of exposure to the risk factors covered in the final rule.
Further, as described below in part C of the risk assessment, OSHA has
refined its analysis, based on data in the record, to estimate the
number and incidence of MSDs occurring among those workers who are
exposed to risk factors at levels that meet the final rule's screen;
OSHA believes that this refinement will ensure that the Agency is
accurately stating the risks posed to employees covered by the final
rule.
The United Auto Workers (Ex. 32-185), argued that OSHA was
underinclusive, not overinclusive, in its choice of the BLS categories
that represent MSDs. In addition to the six categories chosen by OSHA,
the UAW argued that OSHA should have included a substantial fraction of
the injuries and illnesses categorized as ``other'' and ``multiple
injuries'' as well. OSHA agrees that these injury categories contain
MSDs that are relevant to OSHA's risk analysis. However, since data are
not available to describe the proportion of the injuries classified
under these categories that are, in fact, MSDs, the Agency has not
included them in its revised risk assessment. This decision also means
that the risks presented by OSHA in its Risk Assessment section and
estimated in the Significance of Risk section are understated.
As explained by OSHA in its preliminary risk assessment for the
proposed rule, risk estimates based on the BLS data understate the true
risk of incurring a work-related MSD posed to employees who are exposed
to workplace risk factors that are associated with the development of
MSDs, for several reasons. First, the BLS data include only those lost
workday (LWD) cases that resulted in at least 1 day spent away from
work, and thus do not capture either non-lost workday MSD cases nor MSD
cases that resulted in the employee being temporarily reassigned to
another job. Second, some LWD MSDs reported to the BLS by employers are
likely to have been coded in BLS injury categories that are excluded
from OSHA's categories of overexertion, repetition, and bodily reaction
(bending, climbing, crawling, reaching, twisting); for example,
injuries due to segmental vibration are included in BLS event
categories other than those included by OSHA in its analysis, and, as
pointed out by the UAW (Ex. 32-185), the non-specific BLS injury
categories of ``other'' and ``multiple injuries'' are also likely to
contain MSDs.
Finally, the incidence of MSDs reported by the BLS is the reported
incidence of MSDs occurring among all workers in the industries
surveyed (on a full-time-equivalent basis); that is, the incidence for
each industry sector is calculated by BLS as the number of MSD cases
reported in 1996 divided by the total number of full-time equivalent
employees in that industry sector in 1996. Expressing the incidence in
this way has the effect of diluting the estimated incidence of
disorders that are actually occurring among exposed employees, i.e.,
those who routinely are exposed to workplace risk factors that have
been associated with the development of work-related MSDs. The risk to
exposed employees is substantially higher than the risk reflected by
the BLS estimates of MSD incidence, because most of the injuries
reported to the BLS will in fact have occurred among that subset of
workers whose jobs expose them to these risk factors (that is, if the
incidence were calculated using the much smaller denominator that
reflects the number of exposed employees, the resulting incidence
estimate would be higher). Evidence that workers exposed to workplace
risk factors are at substantially higher risk than other workers in
their industry comes from the large data base of formal scientific
studies of exposed worker populations that have demonstrated a positive
relationship between exposure to workplace risk factors and the
relative risk of developing an MSD (see the Health Effects section of
this preamble). These studies show that the prevalence of MSDs among
exposed employees is often 2- or 3-fold higher, and can be as much as
10 to 20 times higher, as the prevalence among workers who are not so
exposed.
In the next part of the Final Risk Assessment, OSHA presents two
alternative approaches to quantifying risks posed to workers who are
exposed to biomechanical risk factors on the job. The first approach is
the same as that used in the Preliminary Risk Assessment presented in
with the proposed rule. In that approach, OSHA's estimates of the risk
are based on the numbers and incidence of MSDs reported by BLS (based
on OSHA's definition of MSDs) by industry sector and by occupation.
OSHA's second approach responds to a number of comments made in the
record that the Agency's Preliminary Risk Assessment did not (1)
properly subtract out MSD cases that occurred among employees who were
not heavily exposed to physical risk factors, and (2) did not properly
account for background risk (i.e., that part of the risk that could not
be attributed to workplace exposure or that occurs among the general
population). To address these comments, the Agency was able to use data
that became available in the record to more precisely characterize the
MSD risk in the subset of employees who are the most heavily exposed to
risk factors covered in the final rule, and to account for background
risk. OSHA's underlying rationale is explained fully in part C below.
C. Results
Table VI-3 provides the BLS estimates of the number of injuries and
illnesses reported nationwide by employers for 1996, by nature of
injury and type of workplace exposure, for all injury and exposure
event categories determined by OSHA to represent the MSDs covered by
the standard. Overall, OSHA estimates that there were a total of
647,344 lost workday MSDs that occurred in 1996, as derived from
employer reports of thoseTable VI-3 here illnesses and injuries. These
disorders represent about 34.4 percent of the 1.88 million LWD injuries
and illnesses reported by employers in 1996 (BLS press release 97-453,
12/17/97).
[[Page 68550]]
Table VI-3.--Estimates of the Number of Lost Workday Musculoskeletal Disorders (MSDs) in 1996, by Nature of Injury and Type of Workplace Exposure
--------------------------------------------------------------------------------------------------------------------------------------------------------
Type of workplace exposure
-----------------------------------------------------------------------------------------------
Nature of injury BLS Code Total for all Subtotal (O Bodily
exposures Overexertion Repetition and R) Reaction \a\ Subtotal
--------------------------------------------------------------------------------------------------------------------------------------------------------
Total for all lost workday injuries..... .............. .............. 526,594 73,796 600,390 79,475 679,865
Musculoskeletal Disorders:
Sprains, Strains, Tears............. 021 819,658 424,290 12,872 437,162 66,068 503,230
Back Pain, Hurt Back................ 0972 52,046 28,046 861 28,907 4,646 33,553
Soreness, Hurt, except back......... 0973 73,542 17,984 5,811 23,795 2,896 26,691
Carpal tunnel syndrome.............. 1241 29,937 .............. 29,809 29,809 .............. 29,809
Hernia.............................. 153 29,624 25,819 322 26,141 670 26,811
Musculoskeletal and connective 17 35,238 7,761 18,278 26,039 1,211 27,250
system diseases and disorders......
---------------------------------------------------------------------------------------------------------------
Total Number of MSDs............ .............. 1,040,045 503,900 67,953 571,853 75,491 647,344
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Data from BLS included only those injuries reporeted to have been associated with ``Bending, climbing, crawling, reaching, twisting.'' Source: BLS-
reported estimates for BLS nature-of-injury codes 021, 0972, 0973, 1241, 153, and 17, and for BLS exposure events of overexertion, repetition, and
bodily reaction (1996).
For 1998, the BLS estimated that there were 592,500 MSDs that
occurred throughout U.S. industry, representing an 8.5-percent decline
from 1996 (``Lost-Worktime Injuries and Illnesses: Characteristics and
Resulting Time Away From Work, 1998,'' U.S. Bureau of Labor Statistics,
available at http://www.bls.gov/news.release/osh2.nr0.htm). This
decline is consistent with the pattern seen from 1992-1996, when both
MSD and overall injury rates declined. For the final risk assessment,
OSHA has continued to use 1996 BLS data in order to be consistent with
the economic analysis, which uses 1996 as a base year throughout. For
example, 1996 is the base year from which data are used to estimate
numbers of establishments and employees, revenues, profits, and costs
associated with the final rule.
About 66 percent of the estimated number of MSDs reported to the
BLS in 1996 were categorized by BLS coders as ``sprains, strains, and
tears'' due to overexertion. As discussed in part B above, OSHA
received many comments on the use of BLS data on injuries classified by
the BLS as sprains, strains, and tears; these commenters objected to
including these injuries in the risk assessment on the grounds that
injuries classified as strains, sprains, and tears reflect acute
injuries that cannot be considered MSDs. Based on the evidence and
testimony presented in part B above, however, OSHA has determined that
it is appropriate to include strains, sprains, and tears that are
associated with the exposure events of overexertion, repetitive motion,
and bodily reaction in the universe of relevant MSDs because these
injuries arise from exposure to relevant risk factors. Furthermore,
OSHA believes that, when MSDs result from exposure to the biomechanical
risk factors covered in the final rule, it is not important to make any
distinction between whether those injuries arose from acute or chronic
events. The purpose of the standard is to reduce the risk of MSDs
resulting from exposure to risk factors, regardless of the duration of
the exposure preceding to those injuries and illnesses.
As further evidence of the appropriateness of including strain,
sprain, and tear injuries in the risk assessment, OSHA presented BLS
data in the preliminary risk assessment that provides additional
information on the nature of the injuries and the exposure events
associated with those injuries [64 FR 65931]; these data are reproduced
in Table VI-4. For this analysis, OSHA obtained from the BLS a breakout
of the estimated number of injuries, by body part and by type of
overexertion event. This breakout appears in Table VI-4 and shows that
about 89 percent of these sprain, strain, and tear injuries (379,615)
are comprised of injuries due to lifting /lowering, pushing/pulling,
holding/carrying, or throwing, all of which are activities involving
force. For the remaining 11 percent of the BLS-coded sprain, strain,
and tear injuries, the exact nature of the overexertion exposure was
either not reported by the employer or did not fall into any other
exposure classification under the BLS system. Of the 379,615 injuries
for which the nature of the overexertion exposure was reported, the
majority (88 percent) affected body parts that are consistent with the
kinds of injuries addressed by the final standard, such as the upper
extremities, neck and shoulder, lower extremities, and back. Fifty-two
percent of these injuries represent back injuries due to lifting or
lowering. Only a small proportion (12 percent) of sprain, strain, and
tear injuries reported by the BLS in 1996 affected body parts that are
not relevant to MSDs. Therefore, OSHA is confident that the vast
majority of BLS-coded sprain, strain, and tear injuries are
appropriately included in the estimated number of MSDs for 1996, and
that the judgment of the OSHA expert panel in selecting appropriate BLS
injury and event categories for Table VI-4 here the risk analysis is
confirmed by this additional breakout and review of the BLS data.
[[Page 68551]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.004
The data summarized above have been broken out by the BLS both by
industry sector and by occupation code. In addition, the BLS provided
OSHA with estimates of the incidence of MSDs, as defined above by
injury type
[[Page 68552]]
and cause, for each 2-digit SIC. As explained above, the BLS-calculated
incidence estimates are based on the incidence among all employees
(full-time equivalents) in each industry sector, and therefore
understate the true incidence of work-related MSDs occurring among
workers who are highly exposed to workplace risk factors, i.e., exposed
in jobs that meet the standard's action trigger. Nevertheless, OSHA
believes that these incidence estimates are useful for characterizing
industry-specific MSD risks and for comparing the extent of the problem
between industry sectors covered by the ergonomics program standard.
Table VI-5 provides estimates of the number and incidence of LWD MSDs
in each general industry 2-digit SIC group for which the BLS provided
data. Industries having the highest incidence of MSDs include the
following:
Air transportation (36.6 cases/1,000 workers);
Local and suburban transit (14.7 cases/1,000);
Motor freight transportation and warehousing (14.4 cases/1,000);
Health services (13.8 cases/1,000);
Transportation equipment (13.4 cases/1,000); and
Food and kindred products (12.2 cases/1,000).
Table VI-6 provides estimates of the number and incidence of LWD
MSDs by occupation code for the 75 occupations having the highest
estimated annual incidence of employer-reported MSDs. Because the BLS
does not provide incidence estimates by occupation, OSHA calculated the
incidence using employment estimates from the Bureau of the Census
Employment and Earnings (1996). Occupations having the highest
incidence include:
Driver--sales workers (42.4 cases/1,000 workers);
Machine feeders and offbearers (34.6 cases/1,000);
Public transportation attendants (32.1 cases/1,000);
Nursing aides, orderlies, and attendants (31.6 cases/1,000);
Punching and stamping machine operators (30.4 cases/1,000 workers);
Laborers, except construction (29.1 cases/1,000);
Sawing machine operators (18.9 cases/1,000);
Furnace, kiln, and oven operators, except food (18.0 cases/1,000);
Grinding, abrading, polishing machine operators (17.9 cases/1,000);
Health aides, except nurses (16.9 cases/1,000); and
Licensed practical nurses (16.5 cases/1,000).
[[Page 68553]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.005
[[Page 68554]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.006
[[Page 68555]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.007
[[Page 68556]]
Of the Census Employment and Earnings (1996). Occupations having
the highest incidence include:
Driver--sales workers (42.2 cases/1,000 workers);
Machine feeders and offbearers (34.6 cases/1,000);
Public transportation attendants (32.1 cases/1,000);
Nursing aides, orderlies, and attendants (31.6 cases/1,000);
Punching and stamping machine operators (30.4 cases/1,000 workers);
Laborers, except construction (29.1 cases/1,000);
Sawing machine operators (18.9 cases/1,000);
Furnace, kiln, and oven operators, except food (18.0 cases/1,000);
Grinding, abrading, polishing machine operators (17.9 cases/1,000);
Health aides, except nurses (16.9 cases/1,000; and
Licensed practical nurses (16.5 cases/1,000).
Of the 225 occupations for which BLS provided estimates of the
numbers of employer-reported MSDs and total employment, the annual
incidence of MSDs was 1 LWD case or more per 1,000 workers per year for
178 (79 percent) of the occupations. The data described above reflect
the annual incidence of MSDs estimated to have occurred in 1996 within
general industry sectors and within occupations within this sector.
Past risk assessments conducted by OSHA in other health standards
rulemakings have typically estimated the lifetime risk to workers based
on the assumption that they are exposed to the hazard in question for a
full 45-year working lifetime. These past risk assessments dealt
primarily with chronic, fatal diseases such as cancer. Unlike the
impairments of health caused by many other OSHA-regulated hazards,
however, MSDs are not fatal, although they are often debilitating.
Moreover, a worker can experience more than one work-related MSD over a
working lifetime. As a result, the lifetime risk associated with
exposure to risk factors on the job can be expressed in a number of
ways. One way of doing this is to define lifetime risk as the
probability that a worker will experience at least one work-related
musculoskeletal disorder during his or her working lifetime (45 years).
This probability is calculated as 1-(p),45 where p is the
probability that a worker will not experience a work-related MSD in any
given year (i.e., p is one minus the estimated MSD incidence for 1996
in the industry sector of interest).\1\ For example, the estimated
incidence of MSDs in 1996 for SIC 80, Health Services, is 13.847 lost
workday cases per 1,000 workers. The probability that a worker in SIC
80 will not experience an MSD in any given year is calculated as
1-.013847, or 0.9862 (almost 99 percent). Over 45 years, the
probability that a worker will never experience a work-related MSD is
(.9862)45, or 0.534 (i.e., 53 percent). Therefore, the
probability that a worker in SIC 80 will experience at least one work-
related MSD is 1-0.534, or 0.466 (i.e., 466 per 1,000 workers).
---------------------------------------------------------------------------
\1\ OSHA used two simplifying assumptions when calculating the
probability of experiencing no work-related MSDs in a working
lifetime: (1) Employment in an industry was used as a surrogate for
exposure to ergonomic hazards in that industry. (2) The probability
of experiencing a work-related MSD in any given industry was treated
as if it were identical for workers in that industry who had never
previously experienced a work-related MSD and those who had
previously experienced a work-related MSD.
---------------------------------------------------------------------------
Alternatively, lifetime risk could be defined as the expected
number of work-related MSDs an employee entering an industry will
experience over a working lifetime in that industry. Unlike a
probability, the expected value in such cases can exceed 1. (That is
why, in the table below, one industry is identified in which an
individual who works for 45 years can expect to experience, on average,
more than one work-related MSD during that time.) The expected value
represents the experience of the ``average'' individual, a measure that
reflects the aggregate experience of many individuals.
Both approaches \1\ taken by OSHA to estimate lifetime risk assume
that the risk to a worker is independent from one year to the next,
i.e., that a worker's injury experience in any one year does not modify
his or her risk in any subsequent year. Although this is a reasonable
assumption for the purpose of estimating an average lifetime risk, it
is likely to be the case that the risk will be higher for workers who
have had an MSD and continue to be exposed since musculoskeletal tissue
has already been damaged. Among workers who have not experienced
symptoms of an MSD, the risk to any individual worker in subsequent
years depends on the amount of tissue damage sustained from exposure to
risk factors and that worker's individual ability to repair or resist
continued injury to the point of experiencing an MSD. In addition,
OSHA's approach also assumes that each worker within a given industry
sector (defined by 2-digit SIC) has the same risk. For the same reasons
as discussed above, a relatively small number of workers will, in fact,
experience injury rates far in excess of the average, while a
comparatively large number will experience injury rates below the
average. At this time, data are not available that would allow OSHA to
determine the lifetime MSD risks for subpopulations of workers within
each industry sector, i.e., those subpopulations with higher than
average or lower than average risks, respectively.
---------------------------------------------------------------------------
\1\ In written comments (Ex.32-185-3), the UAW expressed a
strong preference for estimating the lifetime risk as the
probability that a worker will experience at least one MSD in a
working lifetime rather than as an estimate of the lifetime risk
expressed as the expected number of MSDs a worker will experience in
a working lifetime.
---------------------------------------------------------------------------
Another meaning or interpretation of expected value may be more
intuitive: The expected value is the total number of MSDs that may be
expected to occur in a cohort of 1000 workers all of whom enter an
industry sector at the same time and all of whom work for 45 years in
the industry. The expected value of the number of MSDs occurring among
these 1,000 workers over 45 years of employment is calculated as the
annual MSD incidence multiplied by 45. For example, the estimated
incidence of work-related MSDs in 1996 for SIC 80 (Health Services) is
13.847 cases per 1,000 workers, or a frequency of 0.01387. The expected
value of the number of work-related MSDs predicted to occur among those
1,000 workers over 45 years is estimated to be (0.01387*45), or 0.623
(623 per 1,000 workers).
Table VI-7 presents OSHA's estimates of the lifetime risk of
experiencing work-related MSDs, by industry sector. Based on the
probability approach, the estimated probability of experiencing at
least one work-related MSD during a working lifetime ranges from 24 per
1,000 to 813 per 1,000, depending on the industry sector. Based on the
expected value approach, the expected number of work-related MSDs that
will occur in a cohort of workers all entering an industry at the same
time ranges from 24 per 1,000 to 1646 per 1,000, since this approach
recognizes that it is possible for a worker to experience more than one
work-related MSD in a working lifetime.
Several rulemaking participants criticized OSHA's preliminary risk
assessment on the grounds that the Agency's risk estimates made no
allowance or correction for background risk. These participants (see,
for example, Exs. 32-206, 500-223, Tr. pp.10248-9, Exs. 30-3865, 30-
3356, 32-368, 30-4185, 30-3813, 30-1722, 500-221) argued that MSD risks
for specific industries and occupations based on
[[Page 68557]]
BLS data should be compared to the background rate of MSD risk in the
general population to calculate the excess risk associated with work.
Some of these stakeholders asserted that, because OSHA has not done so,
the Agency's estimates here represent only the average MSD risk posed
to a worker in a particular industry or occupation by exposure to ``all
of life's activities.'' OSHA does not agree; the BLS data reflect only
cases that employers have deemed to be work-related. It would be
inappropriate to adjust the MSD rates estimated on the basis of the BLS
data by subtracting from these rates the MSD rates that have been
reported in the general population. When excess risk is calculated by
comparing a population of concern (in this case the employed
population) to a reference population (e.g., the general population),
the proper approach is to compare the total incidence in the population
of concern to the total incidence in the reference population (see
Rothman and Greenland, Ex. 38-240). That is, to estimate the excess
risk of MSDs among workers using the approach suggested by these
commenters, one must have data that describes the incidence of all
MSDs, both work-and non-work-related, in the working population.
Assuming that the MSD rate for the general population is the non-work-
related rate, and then subtracting this rate from the BLS-based rate,
would yield estimates of the work-related, or excess, risk to workers
only if the BLS data truly represented all MSDs occurring among workers
(both on the job and off the job). This is clearly not the case, since
the BLS data are designed only to capture those injuries that are work-
related; the BLS system does not capture those MSDs that occur among
workers that are unrelated to work. Therefore, adjusting the BLS data
by subtracting out MSD rates for the general population would not yield
meaningful estimates of the excess MSD risk to workers.
[[Page 68558]]
[GRAPHIC] [TIFF OMITTED] TR14NO00.008
Some commenters (see, e.g., Ex. 30-3813, Tr. 4102-4108, Exs. 30-
3356, 30-46-28, 30-4564, 30-3865, 30-4185, 30-3368, 30-1897) argued
that, despite screening out some of the background risk, the BLS data
are still overinclusive.
[[Page 68559]]
They pointed out that under the applicable OSHA and BLS guidelines, a
case is considered ``work-related'' if an event or exposure in the
workplace made any contribution to the injury or illness, regardless of
the extent of that contribution. For example, Frank White of ORC
testified that
ORC [and others] question OSHA's ability to make quantitative
determinations of workplace risks based on data that do not allow
OSHA to differentiate between the respective contributions of
workplace and non-workplace factors. In the face of OSHA's own
acknowledgment of the special difficulties associated with
establishing MSD causation compared ``to more traditional workplace
exposures and disorders,'' the use of data that inherently include
conditions caused by both work and non-work exposures to determine
workplace risk is unacceptable. The result, once again, is an
overreaching by OSHA--this time in its estimation of the true
workplace risk--that has the effect of permeating, and effectively
invalidating, the entire proposal. (Tr. 4102)
OSHA interprets Mr. White's comment as saying that, although strictly
non-work-related MSDs are not captured by the BLS system, some
proportion of cases in the system nevertheless represent MSDs that
occur among workers who are not regularly exposed to risk factors, or
whose exposures arise from tasks that are not ``core elements'' of the
job (using the language contained in the proposed rule). In other
words, although there may be some contribution from work to these
cases, exposure to risk factors on the job are no greater that those
encountered during non-work activities.
In this risk assessment for the final ergonomics program standard,
OSHA has relied on BLS injury and illness data in much the same way it
does when evaluating the risks associated with safety hazards. Because
the statistics relied upon by OSHA reflect work-related injuries and
illnesses reported by employers and determined by OSHA to have been
associated with exposure to the risk factors addressed by the final
rule, there is no ``background'' number of injuries and illnesses in
the OSHA data in the sense that BLS data are capturing non-work-related
injuries. In other words, the total number of MSDs that occur in the
workforce are either work-related or non-work-related; BLS counts the
first and the second represents background. Thus, OSHA does not agree
with these commenters that it is necessary to adjust the BLS data per
se to account for such background risk.
However, OSHA does recognize that some fraction of the number of
MSDs estimated from the BLS data represents injuries and illnesses
occurring among employees in jobs that would not be covered by the OSHA
standard. That is, some of the MSDs being captured by the BLS's annual
survey reflect injuries to workers who are not in jobs that meet the
action trigger, e.g., those who may be exposed to risk factors only
infrequently or those whose exposures were not of sufficient duration.
OSHA does not intend the final ergonomics program standard to apply to
these kinds of jobs. Instead, OSHA intends the standard to apply to
those jobs where MSDs have occurred and the employee's exposure to risk
factors was of sufficient duration, magnitude, and frequency to have
contributed to the injury. This concept is reflected in the final rule
in the form of the Basic Screening Tool, which explicitly identifies
those exposure conditions that must be present on the job, along with
an employee's report of an MSD incident, before the employer is
obligated to implement the program. Employers have no obligation to
establish an ergonomics program under the final rule if employees are
not exposed to risk factors at least at the level(s) reflected in the
Basic Screening Tool. Thus, OSHA adjusted, as an alternate analysis,
its estimates of risk based on the BLS data to include only that
portion of the risk that will be addressed by an ergonomics program
developed under the final rule, i.e., that portion of the risk that is
occurring among employees who are exposed to risk factors at least to
the extent reflected in the final rule's screening tool. OSHA is thus
estimating the risk of MSDs occurring among employees who would be
covered in an ergonomics program, i.e., those who are more highly
exposed to biomechanical risk factors.
As explained by OSHA above, the BLS-reported incidence of MSDs
reflects the number of MSDs reported per 1,000 full-time equivalent
workers employed in industry. This incidence figure distributes the
MSDs evenly across all workers in an industry sector or occupation.
However, as demonstrated by the scientific evidence presented in the
Health Effects section (Section V), OSHA has determined that the work-
related risk of MSDs increases with the intensity and/or duration of
exposure. Because of this, MSDs are not, in fact, evenly distributed
across all workers, but are concentrated among the proportion of
workers who are the more highly exposed to biomechanical risk factors.
Thus, the incidence of MSDs among the more highly exposed workers is
greater than that among the lesser-exposed workers; this has been shown
in the almost 200 epidemiological studies reviewed in the Health
Effects section. It is for this reason that OSHA believes that the risk
estimates presented in the first analysis above, which relied on the
BLS-reported incidence estimates by industry and occupation, understate
the true risk among the workers who are more highly exposed to physical
risk factors (while overstating it for workers who are not highly
exposed to risk factors).
OSHA's second approach to estimating work-related MSD risks takes
account of this risk differential between more highly exposed (i.e.,
higher-risk) workers and lesser-exposed (i.e., lesser-risk) workers to
estimate more precisely the risk among those workers who would most
benefit from an ergonomics program. In addition, the risk among the
higher-risk workers is estimated in two forms. One assumes that all of
the risk among the higher-risk workers can be attributed to their
exposure to biomechanical risk factors, i.e., all of the risk is work-
related. OSHA believes this is reasonable because the data used to make
these estimates are the BLS data, which represents MSDs reported by
employers to be work-related. The second form assumes that, despite the
fact that the data derive from reports of work-related injuries, only
part of the risk can be attributed to workplace exposure to physical
risk factors because of the presence of some ``background'' risk among
the higher-risk workers. This background risk represents MSDs that are
not work-related and are attributed to some unknown non-work exposure
to risk factors. OSHA believes that making such an adjustment to the
estimated risk among higher-risk workers leads to an overly
conservative estimate of risk among workers whose jobs will be screened
in under the final rule; however, the Agency is nevertheless making
this adjustment in response to addresses the concerns of those
commenters who argued that OSHA should take account of the
``background'' incidence of MSDs.
The first step in OSHA's second approach to estimating work-related
MSD risks is to estimate the incidence of MSDs for higher-risk and for
lesser-risk workers. OSHA considers the higher-risk workers to be those
workers who are exposed to risk factors at levels that meet the final
rule's basic screening tool; all other workers are considered lower-
risk in the sense that they are exposed to risk factors at levels below
the final rule's screen.
To accomplish this analysis, OSHA relied on data contained in the
record from Washington State's industry-wide survey of workplace
exposure to
[[Page 68560]]
physical risk factors (Ex. 500-41-118); details of this survey are
presented in Chapter 3 (Benefits Assessment) of the Final Economic
Analysis. Data from this survey were used to estimate the percentage of
employees in each major industry group who are exposed to risk factors
that at least meet the level of a ``caution zone'' job under Washington
State's ergonomics standard. The kinds and durations of risk factor
exposures contained in Washington State's definition of a ``caution
zone'' job are similar to those contained in OSHA's Basic Screening
Tool, e.g., generally 2 or more hours per shift of exposure to
repetitive motions, awkward postures, contact stress, or segmental
vibration, or 4 or more hours per shift of keyboarding activity. Both
tools also use the same lifting weight and frequency-of-lift criteria
to screen jobs for force associated with manual handling. Because of
the similarities between OSHA's screening tool and the Washington State
criteria, OSHA believes it reasonable that use of the Washington State
survey data on workplace exposures to biomechanical risk factors will
yield reasonable estimates of the numbers of workers who are exposed to
risk factors at the levels that meet the action trigger of the final
rule. OSHA has used these data, along with data derived from the
epidemiology studies reviewed in the Health Effects section (Section V
of the final rule's preamble), to estimate the number and incidence of
MSDs occurring annually among employees who are exposed to risk factors
at levels meeting the action trigger in the final rule. OSHA's Final
Economic Analysis contains a detailed description of the Washington
State survey data and OSHA's use of these data to estimate the
percentage of workers in each covered industry sector who are exposed
to risk factors at levels that meet the final rule's action trigger.
OSHA's approach to estimating the excess risk of MSDs among exposed
workers is summarized in Table VI-8. From the Washington State survey
data, OSHA estimated the percentage of employees who are exposed to
risk factors that meet the final rule's screen criteria (Column D of
Table VI-8) in each 2-digit industry sector, as well as the number of
higher-risk workers (Column E).
To estimate the incidence of MSDs separately for higher-risk as
compared with lower-risk workers, OSHA assumes that the annual
incidence of MSDs among the higher-risk workers is three times that of
low-risk workers. The justification for this assumption can be found in
the many epidemiology studies reviewed in the Health Effects section of
this preamble (Section V). These studies compared the prevalence or
incidence of MSDs among workers who are regularly exposed to the risk
factors addressed by the final rule with the prevalence or incidence
among the referent (or less-exposed) worker populations. Typically,
these epidemiological studies report observed differences in these
rates as ratios (such as odds ratios, incidence ratios, prevalence
ratios, or other relative risk measures). A compilation of the risk
measures identified in these studies appears in the form of estimated
median and mean risk ratios in Table VI-9, separated by part of body.
As the table shows, median risk ratios for back disorders, neck and
shoulder disorders, and upper extremity disorders are 1.85, 2.7 to 3.3,
and 2.8 to 6.6, respectively. Mean values for back disorders, neck and
shoulder disorders, and upper extremity disorders are 2.4, 4.5 to 5.2,
and 4.4 to 12.6, respectively. Based on these values, OSHA finds that,
in general, employees who are regularly exposed to the risk factors
covered by the final rule are at three times higher risk or, put
another way, will experience a 3-fold higher incidence of MSDs than is
the case for workers who are not so exposed.
[[Continued on page 68561]]