Lower limb amputee gait during stance phase is related to the angular stiffness of the prosthetic foot, which describes the dependence of ankle torque on angular progression of the shank. However, there is little data on angular stiffness of prosthetic feet, and no method to directly measure it has been described. The objective of this study was to derive and evaluate a method to estimate the angular stiffness of prosthetic feet using a simple linear compression test. Linear vertical compression tests were performed on nine configurations of an experimental multicomponent foot (with known component stiffness properties and geometry), which allowed for parametric adjustment of hindfoot and forefoot stiffness properties and geometries. Each configuration was loaded under displacement control at distinct pylon test angles. Angular stiffness was calculated as a function of the pylon angle, normal force, and center of pressure (COP) rate of change with respect to linear displacement. Population root mean square error (RMSE) between the measured and predicted angular stiffness values for each configuration of the multicomponent foot was calculated to be 4.1 N-m/deg, dominated by a bias of the estimated values above the predicted values of 3.8 ± 1.6 N-m/deg. The best-fit line to estimated values was approximately parallel to the prediction, with R2 = 0.95. This method should be accessible for a variety of laboratories to estimate angular stiffness of experimental and commercially available prosthetic feet with minimal equipment.
Novel Method to Evaluate Angular Stiffness of Prosthetic Feet From Linear Compression Tests
Ann Arbor, MI 48104
Department of Mechanical Engineering,
RR&D Center of Excellence,
Department of Human Physiology,
Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received December 10, 2012; final manuscript received July 2, 2013; accepted manuscript posted July 29, 2013; published online September 17, 2013. Assoc. Editor: Kenneth Fischer.
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Adamczyk, P. G., Roland, M., and Hahn, M. E. (September 17, 2013). "Novel Method to Evaluate Angular Stiffness of Prosthetic Feet From Linear Compression Tests." ASME. J Biomech Eng. October 2013; 135(10): 104502. https://doi.org/10.1115/1.4025104
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