Big Steps Forward for Amputees

David S. Barr of Bodfish, Calif., took an 80,000-mile motorcycle trip that spanned North and South America, Europe, Asia, and Africa.

"Only 70 people have ever done anything like it before," Barr said. "There've been more people in outer space than have made this trip."

What makes it more extraordinary is that Barr, 41, is a double amputee. Fighting in Angola in 1981, he lost one leg above the knee and the other below the knee. But that hasn't kept him from riding a two-wheel 1972 Harley Davidson and writing a book about his around-the-world motorcycle trip.

And that is not all. Barr is one of only a handful of double-amputee parachutists who jump with special prosthetics. And he walks 3 or 4 miles a day and mows his own grass.

Advances in prosthetics, and the example set by amputees such as Barr, have shown more and more people that an amputation does not always mean confinement to a wheelchair. At private companies and key centers such as Northwestern University in Chicago and the University of Utah at Salt Lake City, research that sounds like something out of "The Six Million Dollar Man" could give amputees even more control over artificial limbs.

Physical therapist Marie A. Schroeder, chief of the Food and Drug Administration's restorative devices branch, explains that FDA regulates prostheses, but manufacturers do not have to undergo a full review for each new device. Instead, they must register the products and keep a record of any complaints.

"But if there's a significant change in the technology, we could get involved," Schroeder said.

For instance, she said, her branch has seen some interest in implantable electrodes for stimulating muscles in spinal cord injury cases. Such devices would require review by FDA.

Some innovators are also exploring ways to use computers to design and manufacture custom prostheses, to attach muscles directly to a prosthesis, to develop powered fingers with microelectronics, and even to use brain waves to power prostheses.

For thousands of years, inventors have tried to replicate what nature cannot replace. Prostheses have been used since at least 300 B.C., when crude devices consisting of metal plates hammered over a wooden core, were attached to an amputated limb.

Advances in the science of prosthetics burgeon during and immediately after wars, when large numbers of people need to be fitted with artificial limbs. The technology of modern prosthetics has changed little since shortly after World War II.

"There's a real need for revolution in design," said Giovani M. Ortega, research and development project manager at Sabolich Prosthetics & Research in Oklahoma City, Okla., a division of NovaCare. "The systems that we have, have been around for a long time, and at best there have been only improvements. As far along as we've come, we're still far behind many other industries in terms of implementing new technologies."

Estimates of the amputee population in the United States vary widely, from fewer than 400,000 to more than 1 million. About 9 out of 10 amputations involve the leg, from the foot to above the knee.

Three-quarters of all amputations are the result of disease, often cancer or peripheral vascular disease. The latter is a narrowing of the arteries in the extremities that is often associated with diabetes. Most other amputations are the result of workplace or automobile accidents. And a small fraction, perhaps 3 percent, are due to birth defects that constrict bone growth.

Preventing Amputation

Because so many amputations result from disease, considerable attention has been paid to prevention. For example, the American Diabetes Association recommends people stop smoking, which can speed the progress of peripheral vascular disease. Patients with diabetes should monitor their blood glucose levels carefully, eat a healthy, balanced diet, see their doctors regularly, control their weight, and check their feet each day for small cuts or blisters.

Electric blankets and heating pads carry warning labels that say people with diabetes should not use them without talking to their doctors first. This is because people with diabetes may lose sensation in their limbs. Patients can be seriously burned by an electric blanket or heating pad because they cannot feel how hot it really is.

Patients are also advised to develop an exercise plan after consulting with their doctors. Regular exercise maintains strength, flexibility, and blood flow to damaged areas and can help control pain. However, it's important not to stress the legs, feet or joints. Some good exercises are bicycling or easy rowing on a rowing machine. Swimming and aqua aerobics are also good choices.

"We know of many things that can help people avoid amputation, but unfortunately, it's no fun to do daily foot care or wear only proper fitting, well-designed shoes," said Jennifer Mayfield, M.D., chairwoman of the association's Foot Care Council. "Everybody keeps waiting for a magic bullet, and that would be nice, but it's not coming anytime soon."

Richard J. Gusberg, M.D., chief of vascular surgery at Yale University, said one of the first signs of peripheral occlusive disease is claudication, an aching, tired feeling in the leg muscles when they are exercised.

"The vast majority of people with claudication remain stable, or nearly stable, for an indefinite period of time," Gusberg said. In most cases the progress of the disease can be slowed if people control the risk factors, which includes reducing blood pressure, controlling their diabetes through diet or insulin, and reducing cholesterol levels. Regular exercise has also proven effective because it can strengthen circulation, he said.

The drug Trental (pentoxifylline) is approved by FDA for people with peripheral artery disease. Its use can decrease the thickness and stickiness of blood, and can reduce the deformities of red blood cells, so the blood can get through the narrowed arteries, but it is not effective in all patients, Gusberg said. The use of other drugs in treating occlusive disease has largely been abandoned, he said.

If the disease progresses, the patient might develop gangrene, or ulcers in the leg, as blood flow is reduced.

"When people get to that stage, most of them need to be evaluated for a bypass operation," Gusberg said. Replacing the arteries in the lower leg is effective for five years or more in 70 to 80 percent of cases.

Sensory Loss

Another danger with diabetes is a deadening of the nerves in the extremities. John F. Glass, a biologist with FDA's pacing and neurological devices branch, said there are now a variety of devices that measure sensory loss in the affected limbs. In a patient with diabetes, loss of sensation because of nerve damage signals a need for diligence. Even minor injuries, undetected because the feeling is gone and thus left untreated, can become infected easily and lead to gangrene.

"If you're aware of sensory loss, you want to keep a close watch on it," Glass said. "There's a range of measurement devices, from those that detect general loss of sensation, to those that assess the specific degree of sensory loss, or that can quantify sensitivity to pressure or temperature."

Many of the devices are easy-to-use mechanical implements with no significant health risk to patients. One of the simplest is a hand-held device that looks like an old typewriter eraser with thin wires attached to it. The wires are placed on the toes or fingertips to see if there is tactile sensitivity.

Such simple devices are typically not reviewed by FDA before they are made available to the public. They are intended for use by the patient for monitoring only, not self-diagnosis.

"Loss of sensation in an extremity could indicate a lot of other conditions or disorders, so we would encourage the patient to see a physician immediately for a complete physical examination," Glass said.

Unavoidable Limb Loss

Precautions such as Glass advocates can often delay the progression of the disease. Sometimes, though, the loss of a limb is unavoidable. In those cases, physical therapy starts a day or two after surgery. Since more than 9 out of 10 amputations involve one or both legs, physical therapy usually involves the use of parallel bars, and later a walker or crutches. Part of the training involves how to fall and get up safely.

There are other adjustments as well. Barr said the loss of both legs, and covering the stumps with plastic, means his body has become much less effective at cooling itself, so he has to be on the lookout for hyperthermia. And he learned other tricks to cope, as well.

"I'm constantly on the move, never standing still, always readjusting my balance even when I'm staying in one place, because I don't want one particular area on the stump to get sore," Barr said.

Until recently, patients were not fitted with an artificial limb for four to eight weeks after surgery, but new techniques allow the use of a protective foam over a sterile bandage, and the prosthesis can be fit as soon as the day following surgery.

New Prosthetic Materials

For centuries, wood and leather were the only materials for prostheses, but today's physical therapist has a much wider range available, including advanced plastics and carbon fiber, which are much stronger and lighter and more durable.

"The industry is really moving towards composite materials, because they're lighter in weight, easier to work with, and more durable," said Douglas McCormack, vice president of the Amputee Coalition of America.

Silicone-based compounds used to make prosthetic arms, for instance, give the appearance of real skin, unlike the rigid plastic or metal limbs of years ago, and they are more comfortable for the person wearing them. Women can get prosthetic feet with life-like toes for when they wear sandals; men can get legs with the appearance of hair.

But even materials that work out in one application might not work in another.

"We tested a silicone foot at one point. On a machine it was subjected to 300 pounds of stress for a million cycles, and it didn't have any problems. But an amputee broke it within a few minutes. It really surprised us. Torque and other stresses can fatigue the material quickly," said Sabolich's Ortega. "You'd be amazed at the toll that a human body puts on even the strongest material."

New computer programs better determine where and what the forces are. But it's not just a question of choosing a material that will withstand those forces.

"With some of the new materials being developed, we could make a foot to take any of the pressures that the human body will give it," Ortega said. "The problem is it might not have any springiness. You give up flexibility for strength. You have to balance all the considerations in a prosthetic."

Prostheses are typically sold as components, so that someone who has an above-the-knee amputation would be able to choose leg, knee and foot units, often from different manufacturers, depending on their individual needs.

Most of the units are adjustable. Shock absorbers in knees, for instance, can be made more flexible as a person gains controls over the artificial leg. Ankles can be adjusted to the weight and activity level of the patient.

Arm amputees today can choose between prostheses that are powered by a harness and cable attached to the residual limb, or externally powered devices. Powered arms can be controlled by switches mounted inside or outside the socket, that the patient can activate by flexing certain muscle groups.

Energy Requirements

Some prosthetics research is aimed at providing active devices, which do part of the work of the amputated limb, as opposed to passive devices that are controlled by the residual limb. An amputee with prostheses expends two to three times more energy than a nondisabled person to perform even the simplest activities, such as walking across a room or climbing stairs.

"A semi-active system, in which the limb itself performs part of the function, could reduce that energy requirement significantly," said Sabolich's Ortega. "And there would also be a psychological benefit, because the prosthesis would no longer be just a dead limb, but something that is helping."

Ortega said one area Sabolich is researching would provide sensory feedback from the prosthesis to the remaining limb. For instance, in an artificial leg, pressure sensors in the foot would send a mild electrical signal to the thigh muscles when there is pressure on the back, front or sides of the foot.

That kind of feedback would be similar to what they would get with the pressure of the ground against a natural foot, which would make their adjustment to the prostheses go more quickly, Ortega said.

Ortega said prosthetic designs are limited only by how large a power pack the amputee can carry.

"The crucial issue when it comes to trying to introduce any new prosthesis is the energy requirements," said Ortega. "Our muscles are so efficient, in terms of the power that they produce versus the fuel that they use, that we have a difficult time matching it."

Scientists are also working to build a better socket--the part of the prosthesis that attaches to the residual limb.

Dudley S. Childress, Ph.D., of Northwestern University's Rehabilitation Engineering Program, is working on applying the industrial practice known as rapid prototyping to socket production.

Sockets are now produced largely by hand. A cast is made of the residual limb, and plaster is poured into the cast to make a positive mold. The mold is then used to create a plastic or laminated polyester socket that fits over the residual limb.

Childress employs a computer-aided design program to measure the residual limb and design a socket. Then, using a modified "plastic deposition technology" called squirt shaping, a computer lays down small amounts of polypropylene to produce the desired shape, to very tight tolerances. In industry, the technology is used to quickly produce prototypes of everything from car parts to military weapons, to test them before starting mass production.

"Essentially, every socket is a prototype, and there are potentially some significant advantages to applying these techniques to prosthesis manufacture," Childress said. "We can make a socket in about 50 minutes, which isn't bad, but as people continue to work with the technology, it may be possible to get that down even faster."

The process would also allow manufacturers to make sockets out of different types of material than have been used in the past, or alter the thickness or characteristics of the material very quickly.

Another innovation being explored at Northwestern is powered prosthetic fingers. That might be difficult if you were going to match real fingers, he acknowledged, but most of the time that's unnecessary. Picking up a spoon and holding a book don't require much power, just control. Small motor technology and power storage capability have both improved vastly in recent years.

"If you want to do something like squeeze orange juice, you need force," Childress said. "But even for people without a prosthesis, that's tiresome, so we have all kinds of devices to do those jobs for us. So the intent of the powered fingers would be to provide prehensile [wrap-around] force."

Childress said his laboratory is also looking at devices that would improve the "feel" of prostheses over current devices. It would be comparable, he said, to the way power steering reduces the muscle power needed to steer a car, but you can still "feel" the road through the wheel.

Cables in artificial fingers and hands would connect to the muscles of the forearm, either through holes in the muscle that are surgically lined with skin, or tendons could be taken outside the residual limb and covered with skin. Either option would give the muscle the sense of how hard it is working and how fast it is moving.

Mundane, but Important, Needs

Joan E. Edelstein, Ph.D., director of Columbia University's physical therapy program, stresses the need for prosthetics research to focus not just on high-technology improvements, but to the more mundane but critical things such as fit, to make them as comfortable as possible, particularly among the elderly, whose needs may not be fully considered.

"Most patients are older people who have lost a limb because of diabetes, and the assumption is that they're going to be relatively undemanding of their prosthesis," Edelstein said.

Better prostheses for the elderly might prevent skin breakdown and infections, yet hardly any research dollars are being spent in that area, she said, explaining that, "It's not as glamorous as developing better prostheses for sport, or for children, and they are very difficult problems to overcome."

Research often proceeds along several courses at once, she noted, and you can never know which might yield the next major breakthrough.

Robert A. Hamilton is a writer in Franklin, Conn.