Deformable link segment analysis for prosthetic foot-ankle components: Kinematics

Approaches in the literature for estimating prosthetic foot-ankle power typically require calculating the segment deformation velocity. This, in turn, necessitates approximating the segment angular velocity. Methods can be distinguished by the way in which a segment is defined and the assumptions used for estimating the segment angular velocity. However, isolating foot-ankle performance from overall prosthetic system performance is limited by uncertainties in the definition of angular velocity of a deformable segment. A deformable link segment (DLS) analysis is proposed that provides a means for estimating deformation velocity of a deformable segment without first approximating the angular velocity: the deformation velocity and angular velocity are solved simultaneously at each instant during the stance phase of gait. DLS analysis was compared to two approaches in the literature: the distal foot (DF) model and the unified deformable (UD) segment model during over-ground walking for three trans-tibial prosthesis users. DLS and UD segment estimates of deformation velocity were comparable when applied to the UD segment. Furthermore, DLS analysis enables modelling of deformable prosthetic foot-ankle components separately from other prosthetic componentry. The method is proposed as a rigorous approach to estimating angular velocity and deformation velocity of passive prosthetic foot-ankle components for subsequent calculation of deformation power and energy performance of these devices.