Citing limited data to guide selection of the optimal prosthetic foot stiffness, a team of researchers compared forefoot and heel linear stiffness properties across manufacturer-designated stiffness categories and foot sizes.
They found enough variation in measured stiffness across consecutive categories to conclude that mechanical property data for commercial prosthetic feet would be helpful to clinicians during prescription.
Rather than relying solely on manufacturer recommendations, which are typically based on the intended user’s weight and general activity level, the team set out to establish comparable forefoot and heel stiffness data for a better understanding of differences between commercial prosthetic feet, and between feet of different stiffness categories and foot sizes.
Mechanical testing was completed for five types of commercial prosthetic feet across a range of stiffness categories and three foot-sizes, 56 prosthetic feet in total. Testing at two discrete angles was conducted to isolate loading of the heel and forefoot components. Each prosthetic foot was loaded for six cycles while force and displacement data were collected.
Forefoot and heel measured stiffness were both significantly associated with stiffness category, the study’s authors concluded, and there was no evidence that the relationships between stiffness category and measured stiffness differed by foot size. However, they found inconsistencies between the expected
and measured stiffness changes across stiffness categories (i.e., magnitude of stiffness changes varied substantially between consecutive stiffness categories of the same feet).
While statistical results support that, on average, measured stiffness is positively correlated with stiffness category, force-displacement data suggests substantial variation in measured stiffness across consecutive categories.
The open-access study, “Prosthetic forefoot and heel stiffness across consecutive foot stiffness categories and sizes,” was published in PLOS One.