Effects of a powered ankle-foot prosthesis on kinetic loading of the contralateral limb: a case series

Lower-extremity amputees encounter a series of stress-related challenges. Among them is an increased risk of chronic joint disorders. For unilateral, transtibial amputees, we hypothesize that increasing the power output of the trailing, ankle-foot prosthesis during powered plantar flexion could mitigate kinetic loading applied to the leading, contralateral leg during walking. Here, we present a case series that analyzes kinetic factors of unilateral, transtibial amputee gait and forms a comparison between two types of ankle prostheses with varying power outputs. The factors examined here are impact resultant force, peak foot pressure at heel-strike, step-to-step transition work, and knee external adduction moment. The two prostheses are the amputee participant's daily-use passive ankle-foot prosthesis and the BiOM powered ankle-foot prosthesis capable of biologically accurate powered plantar flexion during late stance. In a preliminary study on two transtibial amputees walking over level terrain at a controlled speed (1.25 m/s), we observed average reductions of 8% in peak impact resultant force, 18% in impact resultant force loading rate, 8% in peak heel-strike foot pressure, and 15% in the 1(st) peak knee external adduction moment when the powered ankle-foot prosthesis was compared to the conventional passive prosthesis. Overall, our preliminary results suggest that more biomimetic prosthetic ankle-foot push-off during late stance may limit leading-leg musculoskeletal stress in walking.