Effect of Asymmetric Foot Placement and Reduced Weight-Bearing Asymmetry on the Sit-to-Stand Task of a Unilateral Transfemoral Amputee

Abstract

The Sit-to-Stand (SiSt) task is one of the most crucial yet mechanically demanding daily tasks. A transfemoral amputee develops high torques on the intact leg to complete the SiSt task. Such high torques are a consequence of limited torques produced by a prosthesis. The main interest of this project is on the sit-to-stand task of a transfemoral amputee fitted with an active knee and passive ankle prosthesis. The objective is to test whether strategies like asymmetric foot placement and reduced weight-bearing asymmetry could reduce the torque produced in the intact knee. Musculoskeletal model of an able-bodied human subject and a transfemoral amputee subject enabled with an active knee prosthesis is developed. Forward dynamic optimisations are performed by defining an appropriate framework required for simulating the sit-to-stand task. The process was verified by implementing the framework on the musculoskeletal model of an able-bodied individual and comparing it with experimental results available in the literature. The comparison showed a good agreement of simulated results with results reported in the literature. Joint torque profiles of the intact limb of the amputee model were then simulated with asymmetric foot placement and reduced weight-bearing asymmetry strategies. Placing the prosthetic leg posterior to the intact leg reduced the peak intact knee torques by 1.5% relative to placing the intact leg adjacent to the prosthetic leg. The peak intact knee joint torques were reduced by 13% in SiSt task simulation with reduced weight-bearing asymmetry. An increased metabolic cost needed to perform the SiSt task also resulted from this strategy.