Optimal Powered Ankle-Foot Prosthesis Torque Profiles to Improve Walking Performance for Individuals with a Unilateral Transtibial Amputation

Prosthetic ankle-foot devices provide valuable assistance for individuals with a unilateral transtibial amputation (TTA) to effectively engage in daily living activities, although users often experience diminished walking performance such as increased metabolic cost, knee joint loading, and dynamic balance asymmetry due to the lack of torque control from commonly prescribed passive devices. Consequently, active powered prosthetic devices have been developed; however, it is unclear how to optimally tune them. The purpose of this study was to identify the optimal ankle torque profile of a powered ankle-foot prosthesis that improves walking performance for individuals with TTA. Specifically, we used a musculoskeletal simulation-based optimization framework to optimize a powered prosthesis torque profile while emulating group averaged kinematics and ground reaction forces. We compared the metabolic cost, knee joint loading, sagittal plane dynamic balance symmetry and torque profiles across the following simulated conditions: a passive prosthesis tracking individuals with TTA walking data, a powered prosthesis tracking able-bodied walking data and a powered prosthesis that separately minimized metabolic cost, knee joint loading, and dynamic balance asymmetry. Distinct torque profiles emerged for each measure, but there was no clear trend in the positive prosthetic work performed, which suggests increased prosthetic work alone is insufficient to improve walking performance. Further analysis showed the prosthetic torque must be properly timed over the gait cycle to improve each measure. This work provides a framework for future work developing customized controllers for powered prostheses to improve various aspects of walking performance of individuals with TTA.