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Impact Testing of Prosthetic Feet for High-Activity Prosthesis Users

A Pilot Study

Nickel, Eric, MS; Voss, Gregory, MBA; Morin, Steve; Koehler-McNicholas, Sara, PhD; Hendershot, Brad D., PhD; Schnall, Barri L., MPT; Gravely, Amy, MA; CPO, Kyle Barrons, MSOP; Mion, Spencer, MHA MBA CPO; Hansen, Andrew, PhD

JPO: Journal of Prosthetics and Orthotics: February 20, 2019 - Volume Online First - Issue - p
doi: 10.1097/JPO.0000000000000252
Original Research Article: PDF Only
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Introduction There is currently no accepted test standard for prosthetic feet to demonstrate durability to impact loading such as that encountered in physically demanding professions (e.g., construction, farming, or military service). The goal of the study was to build a system to pilot test the impact resilience of a selection of prosthetic feet marketed for high-activity prosthesis users.

Materials and Methods Three specimens each of nine prosthetic feet (n = 27 total) were selected by prosthetists at the Minneapolis VA Health Care System (with specifications in accordance with an associated human-subjects research study, n = 3). Maximum drop height without failure was used to assess impact resilience. Drop testing was performed using a custom system with an electromagnet to lift and release a weighted frame in increments of 10 cm until failure. The test specimens were organized into three sets, each with one specimen of each foot with the spring category for a particular user mass. Sets A, B, and C were tested with 45.9, 57.8, and 61.5 kg, respectively (101, 127, and 135 lb, respectively) simulating the mass of the user plus an added 22 kg (48 lb) of worn/carried load, then divided by two to represent even load distribution to both legs at impact.

Results The feet withstood drop heights without failure ranging from 20 cm to 100 cm. The type of foot was found to significantly affect maximum drop height (P = 0.014). Effect sizes for comparisons of individual feet range from 0.15 to 3.17 with the median effect size being 0.94, which is considered “large.”

Conclusions The test system successfully measures impact resilience and is sensitive to foot type. Large effect sizes indicate substantial differences between prosthetic feet marketed for active prosthesis users.

ERIC NICKEL, MS; GREGORY VOSS, MBA; STEVE MORIN; SARA KOEHLER-MCNICHOLAS, PHD; AMY GRAVELY, MA; KYLE BARRONS, CPO, MSOP; SPENCER MION, MHA, MBA, CPO; and ANDREW HANSEN, PHD, are affiliated with the Minneapolis VA Health Care System, Minneapolis, Minnesota.

BRAD D. HENDERSHOT, PHD; and BARRI L. SCHNALL, MPT, are affiliated with the Department of Rehabilitation, Walter Reed National Military Medical Center, Bethesda, Maryland.

BRAD D. HENDERSHOT, PHD, is affiliated with the DoD-VA Extremity Trauma and Amputation Center of Excellence, San Antonio, Texas.

BRAD D. HENDERSHOT PHD, is affiliated with the Department of Rehabilitation Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.

ANDREW HANSEN, PHD, is affiliated with the Department of Rehabilitation Medicine, University of Minnesota, Minneapolis, Minnesota.

Disclosures: Support was provided by the BADER Consortium via the Congressionally Directed Medical Research Program (award number W81XWH-11-2-0222). There are no potential conflicts to report.

Correspondence to: Eric Nickel, MS, 1 Veterans Dr (Mail Stop 151–Research), Minneapolis, MN 55417; email: Eric.Nickel@va.gov

© 2019 by the American Academy of Orthotists and Prosthetists.