trajectory of the center of rotation in non-articulated energy storage and return prosthetic feet

non-articulated energy storage and return prosthetic feet lack any true articulation or obvious point of rotation. this makes it difficult to select a joint center about which to estimate their kinetics. despite this absence of any clear point of rotation, methods for estimating the kinetic performance of this class of prosthetic feet typically assume that they possess a fixed center of rotation and that its location is well approximated by the position of the contralateral lateral malleolus. to evaluate the validity of this assumption we used a finite helical axis approach to determine the position of the center of rotation in the sagittal plane for a series of non-articulated energy storage and return prosthetic feet. we found that over the course of stance phase, the sagittal finite helical axis position diverged markedly from the typically assumed fixed axis location. these results suggest that researchers may need to review center of rotation assumptions when assessing prosthetic foot kinetics, while clinicians may need to reconsider the criteria by which they prescribe these prosthetic feet.