Energy storage and stress-strain characteristics of a prosthetic foot: a priori design and analysis with experiments

This work proposes an experimentally validated numerical approach for a systematic a priori evaluation of the energy storage and stress-strain characteristics of a prosthetic foot during the stance phase of walking. Boundary conditions replicating the rocker based inverted pendulum model were incorporated. The mechanically complex Ottobock Solid Ankle Cushioned Heel (SACH) foot was opted as the test device. A non-linear finite element (FE) model of the device was developed inclusive of its sources of non-linearity. A custom rig was fabricated to investigate the prosthetic foot's mechanics in a gait analysis facility and experimentally validate the finite element approach. The numerical and experimental outcomes showed fair agreement, with the centre of pressure at the foot-floor interface deviating by 1.56 mm at the instance of highest strain. The magnitude and the distribution of the energy stored and a series of stress and strain parameters were analyzed for the test device using the proposed approach. The novel methodology proposed may act as an effective tool for the design, analysis, and prescription of energy storage and return prosthetic feet.