Human Variation In Midstance Foot Shape Generated From Plantar Pressure

PURPOSE: The human foot plays an integral role in single and double stance support and bipedal locomotion. Previous studies have analyzed variation in plantar pressures during walking. However, plantar pressure also has the potential to be applied to studying shape variation in the human footprint relative to foot morphology. We present a novel approach to generate three-dimensional surfaces from plantar pressure data at midstance with arch shapes categorized as high, normal, or low arch by the Arch Index (AI). METHODS: A pressure sensitive-mat was used to obtain a dynamic left footprint of 49 young (ages 18-52), healthy adults (32 females, 17 males). Three-dimensional surfaces were generated from plantar pressure data at midstance in MATLAB with the x and y dimensions representing foot positioning on the force plate and the z dimension representing the ground reaction force. Foot shape was analyzed using a three-dimensional geometric sliding semilandmark analysis (195 semilandmarks) in MATLAB. Semilandmarks were slid to minimize the energy of bending of the thin plate spline interpolation function. Final semilandmarks underwent a Generalized Procrustes Analysis and variation was determined using a principal components analysis and resampling statistics based on Procrustes distances between subjects. RESULTS: A statistically significant (p < 0.05 for all pairwise comparisons between groups) difference in whole foot shape between individuals categorized as high, normal, and low arch heights exists. The three foot types separate along the first three principal components (representing 38.25% shape variation). There is no statistically significant difference between males and females whole foot shape (p = 0.999). CONCLUSIONS: Variation in whole foot shape suggests differences in the support and locomotion patterns among humans of different foot types. This is consistent with previous studies investigating plantar pressure differences; however, no study has characterized overall foot shape. Analyzing three-dimensional surfaces generated from plantar pressure data allows for an increased understanding of the impact of human anatomical characteristics on the shape and plantar pressure forces. Future research aims to analyze variation relative to other clinically relevant characteristics.