Analysis and optimization of passive knee prosthetic design parameters over varying cadences

Abstract

The need for effective prostheses is prevalent worldwide, and is especially dire in developing countries and low-resource settings. The MIT GEAR Lab is addressing this gap through the ATKnee, a low-cost, passive prosthetic knee that employs the use of spring and damper components to replicate the knee torque of the able-bodied human knee. In this study, we build upon prior work to optimize the components used in the ATKnee by accounting for results from field-testing. We first develop an inverse dynamics model to confirm understanding of previous work. We then use a genetic optimization algorithm to optimize parameters across different walking speeds and various spring-damper configurations. The best fit, as measured by the highest R2 value, is obtained when a viscous damper is active during the first dissipative phase (b*11 ), a friction damper is active during the second dissipative phase (b*/20 ), and an additional friction damper is active throughout both phases (b*/0). We make the suggestion that b*/0 = 0.084, b*/11 = 0.008, b*/0 = 0.183, gives the most optimal passive system knee torque with the engagement and disengagement timings teng = 51.3%, tdis1 = 64.2% for the first damper, and teng2 = 86.1%, tdis2 = 95.2% for the second damper. We find that the parameters are robust to subject body mass, but show a positive correlation with walking speed. We conclude that while we are able to suggest an optimized parameter set that includes higher order dampers, it will be important to investigate the effects of cadence, as well as to study the joint torques at the hip, which is further from the foot.