Effect of Foot Shells on Mechanical Properties of Prosthetic Foot Systems

Abstract

Prosthetic foot systems are typically composed of both structural keel and foot shell components. The interaction between these components is considered by the prosthetic device industry with respect to designing higher performance systems with strategically paired components. However, the influence of foot shells on prosthetic foot system mechanical performance is limited in academic literature.

The overall goal of this study was to inform future prescription guidelines and design practices of prosthetic foot components by quantifying the effects of foot shells on mechanical properties of prosthetic foot systems. A methodology was proposed enabling characterization of midstance properties that was adapted from a protocol used to predict continuous deformation characteristics of prosthetic feet throughout stance. The proposed method was validated against previous results, and successfully detected differences related to foot design during midstance loading. Specifically, increased deformation corresponded to earlier double-keel loading initiation and later transition into single-keel forefoot loading.

The new protocol was implemented to quantify effects of various foot shell designs on predicted deformation and stiffness characteristics of prosthetic foot systems. Observed effects on the system included path-dependent changes to the force-displacement curves, instances of both decreased and increased stiffness up to 73% and 49%, respectively, and up to 13% increased durations of double-keel loading. Varied effects were observed depending on keel and foot shell design, and phase of stance.

In a final study, effects of isolated foot shell design features on mechanical performance of prosthetic foot systems were investigated. Results indicate a complex interaction likely exists between keel and foot shell components, and should therefore be taken into further consideration in the evaluation, design, and prescription of prosthetic foot systems.