Compliant orthoses for repositioning of knee joint based on super-elasticity of shape memory alloys

Abstract

People suffering from neuromuscular diseases may also face certain abnormalities in their walking pattern. Patients with quadriceps muscle weakness suffer from flexion contracture as well as flexion instability during the gait cycle. In this article, a knee-ankle-foot orthosis design is proposed with two different mechanisms for the stance and swing phases, addressing the needs of patients with quadriceps muscle weakness. The stance phase mechanism locks the knee joint movement from the initial contact until the end of mid-swing and after mid-stance phase, the knee joint can flex freely. OpenSim was utilized to simulate patients with muscle weakness as well as calculating the required moment to mimic the stiffness of a normal knee joint. The super-elasticity of shape memory alloys was then used to reproduce the calculated moment for different levels of muscle weakness. It is shown that by designing patient-specific orthosis, the stiffness profile of normal joint for each patient with distinct level of muscle weakness can be reproduced.