Biomechanical and energetic effects of knee flexion control during incline walking for users of the Power Knee.

Abstract

Individuals with transfemoral amputation often report difficulty with ambulating on inclined surfaces. Conventional prosthetic control strategies typically apply a level walking controller in incline walking modes, which may not be biomechanically optimal. Able-bodied individuals modulate knee stance pre-flexion substantially during incline walking, which is absent in most prosthetic level walking controllers. However, the biomechanical effects of stance pre-flexion for users with robotic microprocessor-controlled knees are not well-explored during inclines. In this study (n = 10), we investigated the joint kinematics/kinetics/power, biological joint level work and metabolic energy cost to evaluate the biomechanical effects of stance pre-flexion on a 7.5^o incline walking using a commercially available robotic prosthetic knee, the Össur Power Knee, and a passive foot, the Össur Pro-Flex LP. We ran a Bradley-Terry model to rank user preferences on stance pre-flexion conditions. We found that a 16.7 % reduction on the contralateral biological ankle joint positive work during stance phase when stance pre-flexion increased (p < 0.01). However, there was no significant difference in metabolic energy cost. Survey data revealed participants preferred higher stance pre-flexion angles (12^o -18^o) compared to lower angles (0^o - 6^o), indicating consistent preference towards increased stance pre-flexion on inclines. Our results indicate that reduction in biological joint work associated with stance pre-flexion emphasizes the need to implement stance pre-flexion adjustments in prosthesis controllers, as opposed to using a level-walking controller.