Finite Element Simulation of Prosthetic Foot Adaptation to Mediolateral-Angled Cross-Slopes

Introduction: Balance, functional mobility, satisfaction with participation, residual limb comfort, and falls are persistent problems for people with lower-limb amputations (LLAs). Limitedmediolateral accommodation of foot prostheses to cross-slope and uneven ground has been suggested to contribute to these problems. The purpose of this study is to examine how variations of prosthetic foot stiffness, width, and split toes alter mediolateral and vertical displacement, forward velocity, and ground-foot orientation during the stance phase of gait on cross-slopes using finite element computer simulation. Materials and Methods: Model construction (material data, geometry, and mesh) and simulations were performed using Ansys LS Dyna. Durawalk foot geometry was used as the base model. Variations included cross-slope angle (5 degrees increments from 10 degrees to -10 degrees), foot stiffness, body mass, foot width, and number of splits. Lateral deviation (millimeter), vertical displacement (millimeter), and change in forward velocity (% of initial) were obtained from the proximal pylon. Foot contact was measured as a percent of the base model foot width. Results: For a given foot stiffness, mediolateral displacement, inferior vertical displacement, and forward velocity increased with increased cross-slope. Reduced foot stiffness decreased mediolateral displacement and increased foot contact, inferior vertical displacement, and forward velocity on cross-slopes. Wider foot design increased foot contact but increased mediolateral displacement on cross-slopes. Single- and double-split toes creating two or three cantilever springs improved foot contact and reduced mediolateral displacement compared with full-toe variations. Conclusions: For full-width foot variations of stiffness, body mass, and width, properties that enabled maintenance of forward velocity during flat-ground walking gait resulted in mixed effectiveness on cross-slopes. Reducing foot stiffness resulted in deformation of the foot on cross-slopes, which reduced mediolateral displacement but increased forward velocity and vertical displacement. Increasing foot stiffness maintained vertical position and forward velocity but reduced foot contact and increased mediolateral displacement. Full-length splits of the foot into two or three cantilever springs resulted in less mediolateral displacement and improved foot contact. Full-length splits reduced performance changes from flat ground to cross-slopes compared with full-width prosthetic feet. Future studies will be necessary to determine which variations are optimal and if these results are sufficient for comfort, skin integrity, and performance for people with LLA who use prosthetic feet.