Impact testing of prosthetic feet for high-activity prosthesis users: A pilot study

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.