The effect of single and multiple split-toe designs on cross-slope adaptability of prosthetic feet: a finite element simulation study.

Abstract

ABSTRACT Introduction During activities of daily living, the foot-to-ground contact orientation changes in the frontal plane. The adaptability of a prosthetic foot in the frontal plane may improve functional mobility, comfort, and safety. Current prosthetic feet may or may not have a longitudinal split in the toe portion of the foot. The single-split (two-toe) prosthetic foot has been recommended for adaptability on uneven ground compared with feet without longitudinal splits. The purpose of this study was to evaluate the effect of single and multiple split-toe cantilever spring designs of prosthetic feet on cross-slopes using finite element simulation. Materials and Methods Model construction (material data, geometry, and mesh) and simulations were performed using Ansys LS Dyna. A virtual mass of 75 kg, representing body mass, was fixed to the proximal pylon. Foot variations with one to six toes were created by modifying the base geometry with zero to five splits. Walking surfaces that were either flat or a 15-degree cross-slope was virtually fixed in space. The simulation was started at midstance with the pylon in a vertical position and was continued for 0.2 seconds. An initial velocity of 1 m/s was applied to the proximal mass. Lateral deviation, and vertical displacement and mediolateral contact forces of the simulated body mass were calculated. Von Mises stresses, indicating the potential for material failure, were evaluated. Results On level ground, after 0.2-second simulation, feet were comparable in outcomes. On a 15-degree cross-slope, lateral deviation of the body mass decreased with increasing splits from 15.5 mm with no splits to 6.9 mm with the five-split variation. Consistent with this finding, maximal and average forces at the pylon-body mass connection also decreased with increasing splits. Von Mises stress values increased at the proximal toes with increasing splits consistent with narrowing of each toe. Discussion and Conclusions The current study showed that the benefit of increasing the number of toes was most significant with the first split and diminishing returns as the number of splits increased beyond three. Adaptability of split-toe variations may have benefits beyond cross-slopes because there are many instances during activities of daily living where the foot-to-ground angle may change. These findings should be tested using other research methods such as biomechanical studies of multiple split-toe prosthetic feet, and if these results are supported, clinical trials may be warranted. Clinical Relevance This study supports the use of split-toe prosthetic feet for people who want more frontal plane adaptability during gait or who have lateral pressures at the socket. The study predicts that prosthetic feet with more than one split could provide more adaptability and should be explored for clients.