A Study of Multifunctional Slope Adaptive Behaviors in Ankle Prostheses

Abstract

While carbon fiber spring prostheses remain the standard in transtibial prostheses, an increasing number of multifunctional prostheses – those that provide different behaviors than a simple spring, such as hydraulic damping – have started to emerge. This thesis evaluates two multifunctional behaviors relative to a fixed-angle spring. One introduces damping in the mid-stance range of motion, which becomes a simple spring outside that range. The other also introduces conformal damping in the mid-stance range of motion, but incorporates a variable spring equilibrium angle to adapt to slopes. To assess these three behaviors in a consistent manner, a robotic ankle prosthesis emulator was used and controlled real-time from Simulink. It is expected that the spring will provide the best energy return and symmetry of gait, but the hydraulic damping will reduce socket moments, especially on inclines. The equilibrium-adjusting behavior should provide energy benefits similar to a simple spring, with reduced socket moments due to the conformal damping. Three participants walked with each ankle behavior on level, inclined, and declined angles. From motion capture and ground reaction force data, the energy return, symmetry of step length, and average socket moment were calculated for each step. The conclusion is threefold: 1) mid-stance damping increases comfort; 2) however, mid-stance damping decreases energy return and reduces step symmetry on level ground; 3) by introducing a variable spring equilibrium with mid-stance damping, the ankle can provide both increased comfort on level ground and slopes without sacrificing energy return and step symmetry.