Center of Rotation Position in Non-articulated Prosthetic Feet: Implications for Prosthetic Foot Kinetics

Joint kinetics have been estimated via inverse dynamics with link-segment models to analyze the performance of non-articulated energy storage and return (NA-ESR) prosthetic feet [1] and to examine the motor control strategies and compensations adopted by lower limb amputees [2]. A central assumption of the link-segment model commonly used in this application is that the ankle’s axis of rotation acts as a fixed hinge; yet in NA-ESR prosthetic feet, no true ankle articulation exists, and the extent to which any axis remains fixed is unknown. Despite these concerns, this computational approach has been used to assess differences within and between amputees, and in comparison to non-amputees [1,3]; thus reports of estimated kinetics in NA-ESR prosthetic feet, and proximal joints may be in question [4]. Two groups have attempted to address this concern [4,5], yet neither reported the actual axis location. Additionally, the feet tested previously are not commonly prescribed in clinical use today. The overall objectives of our work are to discern the magnitude of ankle joint axis mis-location required to induce meaningful alterations in joint kinetics, evaluate the center of rotation position in a series of NA-ESR prosthetic feet, and quantify the effect of any differences in center of rotation position on prosthetic foot and proximal joint kinetics of a unilateral transtibial amputee. The primary focus of this paper is the quantification of the center of rotation position in NA-ESR prosthetic feet.