Replacement of an active metatarsophalangeal joint with a passive spring-damper system for implementation in an ankle prosthesis

Abstract

Analytical modeling was used to determine the optimal configuration of a replacement metatarsophalangeal (MTP) joint to be used in a prosthetic ankle. A spring was added to the joint to store energy and release it during the part of the gait cycle where the highest torque is required, reducing the torque the motor must exert. A linear spring-damper system adapted for use on a rotational joint was found to exhibit similar behavior to the biological joint for the range of motion required. The optimal gear ratio for the ankle motor, spring constant, and damping constant for the MTP joint were found using a MATLAB program written for this purpose. A physical prototype was fabricated, and testing was performed on an Instron machine to validate the results.