The influence of load carriage and prosthetic foot type on individual muscle and prosthetic foot contributions to body support and propulsion.

Individuals with transtibial amputation (TTA) experience altered gait mechanics, which are primarily attributed to the functional loss of the ankle plantarflexors. The plantarflexors contribute to body support and propulsion and play an important role in adapting to different load carriage conditions. However, how muscle function is altered across different prosthetic foot types and load carriage scenarios for individuals with TTA remains unclear. This study used musculoskeletal modeling and simulation of human movement in OpenSim to investigate the effects of a range of prosthetic feet and load conditions on individual muscle and prosthetic foot contributions to body support and propulsion. Twenty walking trials were collected from five individuals with TTA, consisting of five loading conditions (no-load; 30 lbs (13.6 kg) carried as a front-load, back-load, intact-side-load and residual-side-load) while wearing four prosthetic feet (their passive standard of care (SOC) foot, their SOC foot one category stiffer, their SOC foot with a heel stiffening wedge, and a dual-keel foot). Two participants also wore a powered ankle-foot prosthesis, thus completing an additional five trials each. The results indicated that the front-load condition may be more challenging because it required overall increased muscle contributions to body support and propulsion. However, the front- and residual-side-loads required reduced intact-side plantarflexor contributions to support and propulsion, and thus may be advantageous for individuals with plantarflexor weakness. Further, the large variability across contributions suggests that individuals with TTA may rely on a variety of compensatory mechanisms depending on the load condition and prosthetic foot used.