The influence of load carriage and prosthetic foot type on measures of biomechanical demand

Individuals with transtibial amputation (TTA) are at increased risk for conditions such as intact-limb osteoarthritis and fatigue, likely due to elevated joint loading and metabolic cost compared to unimpaired individuals. These risks are amplified during load carriage, as individuals with TTA lack residual limb ankle plantarflexors and rely more heavily on their intact limb to meet increased mechanical demands. This study used musculoskeletal modeling and simulation to evaluate how different prosthetic feet and load carriage positions affect biomechanical demand during steady-state walking. Measures included total metabolic cost, individual muscle contributions to metabolic cost, and intact limb axial knee joint impulses. Walking data were collected from five individuals with TTA across five loading conditions (no-load and 30 lbs. carried as a front-, back-, intact-side-, or residual-side-load) while wearing four prosthetic feet (a passive standard-of-care foot, a stiffer foot, a heel-wedge-modified foot, and a dual-keel foot). Two participants also completed additional trials using a powered ankle-foot prosthesis. Front-load carriage resulted in the highest metabolic cost (7.56 ± 0.40 W * kg^-1) while back-load carriage had the lowest (6.34 ± 0.38 W * kg^-1). Key contributors to increased metabolic cost included the gastrocnemius, soleus, gluteus maximus and gluteus medius. Front-load carriage had the lowest intact knee joint impulse (16.56 ± 1.33 N * s * kg^-1) while intact-side-load carriage had the highest (20.60 ± 1.39 N * s * kg^-1). The optimal prosthetic foot varied greatly depending on load carriage position or biomechanical demand. These findings highlight the importance of tailoring both load carriage strategies and prosthetic foot prescriptions to the individual to optimize outcomes.