Low-profile prosthetic foot stiffness category and size, and shoes affect axial and torsional stiffness and hysteresis.
Joshua R Tacca, Zane A Colvin, Alena M Grabowski
PMID 38481976WHAT IT FOUND
Stiffness category, foot size, and adding a shoe changed measured stiffness and energy loss of low-profile prosthetic feet.
A higher category was stiffer. Larger size reduced axial stiffness. Shoes reduced heel and midfoot stiffness and increased energy loss.
Key findings
01Higher stiffness category increased axial stiffness at the heel, midfoot, and forefoot by 4.6, 15.6, and 3.8 kN/m for every 1 stiffness category increase.
02Larger prosthetic foot size decreased axial stiffness at the heel, midfoot, and forefoot by 1.7, 19.4, and 1.6 kN/m for every 1 cm increase in size.
03Adding a shoe decreased heel and midfoot axial stiffness by 13.5 and 81.4 kN/m and increased heel, midfoot, and forefoot hysteresis by 13.8, 11.0, and 7.0 percentage points, but did not significantly change forefoot axial stiffness (p = 0.46).
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study tested prosthetic feet on a machine, not people with amputation, so it did not measure walking, comfort, energy cost, or injury risk. Only one type of walking shoe was tested, so the shoe effects may not apply to all footwear. A uniaxial load cell was used, so off-axis forces could not be directly measured; the authors noted a possible force overestimation and reported a post hoc check showing 1% overestimation. Torsional stiffness was estimated using a constant moment arm, which may have overestimated torque. The tested sample was limited to stiffness categories 1 to 8 and sizes 24 to 29 cm.
Declared interests
The study was funded by a Department of Veterans Affairs Rehabilitation Research and Development Service merit review award (I01 RX002941). The authors declared financial support for the research, authorship, and/or publication.
The easy way to misread this
Do not conclude that a shoe or a higher stiffness category will improve a patient's walking. This was a bench test of prosthetic feet, not a clinical trial, and it did not measure walking outcomes.