Design and development of mechanical metatarsophalangeal joint for powered ankle-foot prostheses

Abstract

This thesis seeks to explore passive designs for a mechanical alternative to the metatarsophalangeal (MTP) joint, a critical anatomical component in human feet which allows for various types of anatomical motion. Our goal is to design a system that will act as a platform to test a proof of concept for a passive ankle-foot prosthesis with an MTP joint, but can also be adapted to use an actuated joint in the future. To increase the user's range of motion, our aim was for the mechanical MTP joint to achieve a maximum 600 dorsiflexion angle. We developed 2 MTP joint designs (Rubber Hinge and Fabric Hinge) with 2 body geometries varying at the heel for each (Traditional Heel and Inverted Heel) for a total of 4 models. We performed a static load Finite Element Analysis (FEA) using the Solidworks FEA Simulation Tool. The FEA was performed under the worst-case static load scenarios for the toe and body components of the prosthesis, standing on tiptoe with a dorsiflexion angle of 60' for the toe components and standing with all weight on the heel for the body components. The simulation yielded that not only did no components experience any irreversible deformation, but that the Rubber Hinge design had a minimum safety factor of 5.7, 10, and 4.5 for the Toe, Inverted Heel Body, and Traditional Heel Body respectively and the Fabric Hinge Design had a minimum safety factor 1.4, 9.9 and 4.5 for the Toe, Inverted Heel Body, and Traditional Heel Body respectively. This informed us that though both designs did not undergo failure under the prescribed loads, material utilization was in excess and could be further optimized to decrease the weight. Future designers should focus on implementing this platform into high fidelity physical models to be tested under various static and dynamic loading conditions as well as further optimizing the dimensions of the prosthesis.