Quantifying the Spring-Like Properties of Ankle-Foot Orthoses (AFOs)

Abstract

ABSTRACT

To assess the ability of a specific orthotics stiffness tester to quantify the biomechanical properties of stiffness and energy return of three different ankle-foot orthosis (AFO) designs. Three different posterior leaf spring AFO designs (standard, chevron, carbon fiber) were fabricated in three different sizes and in three different stiffnesses. Efforts were made to standardize the design characteristics across the different styles to ensure uniformity. Each AFO was tested repeatedly with the orthotic stiffness tester. Stiffness was calculated as the average slope of the angle versus moment plot. Energy dissipation was calculated as the area inside the hysteresis loop. The device was found to be repeatable for stiffness, but not for energy storage. Speed did not affect stiffness calculations. Size was significant. Significant differences were found between stiffness categories (flexible, moderate, and stiff). The orthotic stiffness-testing device appears to be appropriate for use in studies that attempt to optimize orthosis-patient stiffness pairings. It is not adequate for assessing energy storage and return. We intend to match stiffness deficits of individual patients with AFOs of appropriate stiffness to normalize the midstance plantarflexor moment. We plan to improve the design of the orthotics tester to better assess the ability of the AFO to assist with power generation at push-off.