Comparing forefoot and heel stiffnesses across commercial prosthetic feet manufactured for individuals with varying body weights and foot sizes.

Background: Despite the effects of prosthetic foot mechanical properties on gait of people with lower limb amputation, scant forefoot and heel stiffness data exist to help guide prosthetic foot prescription.

Objective: To measure forefoot and heel linear stiffness properties across commonly prescribed commercial prosthetic foot models and to describe variations in stiffness across feet targeted for users with different body weights and foot sizes.

Study Design: Mechanical testing of five types of commercial prosthetic feet across nine user body weight and foot size combinations.

Methods: Linear forefoot and heel stiffness (force vs. displacement) data were collected for 41 prosthetic feet. Quasistatic testing was conducted at -15 and +20 degrees to isolate loading of the heel and forefoot, respectively.

Results: Overall, there was a significant relationship between user body weight and both forefoot and heel stiffness, when adjusted for foot size and type ( P < 0.001). However, there were a substantial number of inconsistencies across foot type within example user body weight and foot sizes combination. Furthermore, the relative order of forefoot stiffness across foot type differed from the relative order of heel stiffness across foot type.

Conclusions: The inconsistencies and differences in relative order of forefoot and heel stiffness across commercial foot type suggest the importance of publishing objective stiffness and other mechanical properties of prosthetic feet. These data can aid clinicians in better matching mechanical properties of prosthetic feet with the functional goals and abilities of prosthesis users.