Morphology of Foot Types

Introduction

     Structurally, the foot can be classified as one of three foot types: pes cavus (high arch), neutrally aligned (normal arch), or pes planus (flat foot, low arch). Classification measurements are typically 2-D or contain a subjective component that limits their accuracy and repeatability. Furthermore, no classification methods are universally accepted as the gold standard. The purpose of this study was to develop a repeatable, objective method to quantify differences of foot structures between foot types based on the 3-D orientations of foot bones. Direct understanding of how the foot structure changes between foot types can assist in diagnosis and improve upon clinical treatment regimes such as orthotic prescription and surgical correction.

Pes cavus feet have a high medial arch, an adducted forefoot and an inverted hindfoot. The foot may be rigid and nonreducible.
Neutrally aligned feet have a normal (well formed) medial arch, and the hindfoot is well aligned, i.e., the calcaneus is perpendicular to the floor.
Pes planus feet have a low medial arch, an abducted forefoot, and an everted hindfoot. These feet are usually flexible and reducible.

Methods

Subjects were classified as either pes cavus, neutrally aligned or pes planus through clinical examination by an orthopaedic surgeon with extensive foot and ankle experience. The pes planus population was further divided into asymptomatic and symptomatic foot types. Partial weight bearing CT scans (GE 8 slice multi-detector Lightspeed Ultra Scanner, 0.5 sec helical scans, 1.25 mm slice thickness, 1.25 slice interval, 0.625:1 pitch) were collected. The subjects were scanned in a supine position, while their feet were placed in a custom designed loading frame that applied a force to the soles of their feet. The force applied was equivalent to 10% of their body weight to simulate weight bearing.

Assuming constant density throughout the bone, the inertial matrices were determined from the bone morphometry; these data served as local coordinate systems and bone-to-bone orientations were described using Z, Y’, X” Euler angles.

Results

One of the relationships of interest is the orientation of the first metatarsal relative to the talus. In the pes planus feet the first metatarsal is abducted (-Y’ angle) with little plantar flexion (X” angle, near zero), pes cavus feet are adducted (+Y’ angle) with large amounts of plantar flexion (+X” angle) and that neutral feet lie between.

		Z	Y'	X"
Pes Cavus		4.30 (± 16.09)	33.60 (± 23.76)	26.66 (± 10.63)
Neutrally Aligned		-7.24 (± 8.16)	-6.57 (± 9.59)	13.53 (± 5.77)
Pes Planus Asymptomatic		-12.13 (± 9.48)	-15.67 (± 5.73)	3.83 (± 6.20)
Pes Planus Symptomatic		-14.07 (± 14.38)	-21.25 (± 12.02)	-0.34 (± 8.02)

Acknowledgement:

This research was supported in part by VA Grant A2180R.

This project is fully described in:

Ledoux WR,  Rohr, E.S., Ching RP,  Sangeorzan BJ. "The Effect of Foot Shape on the three-dimensial position of foot bones", Journal of Orthopedic Resarch, 24(12), 2176-86, 2006

Research Team

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