Design of an implantable radiopaque liquid load sensor from a modified Scandinavian Total Ankle Replacement (STAR) mobile bearing for the in vivo measurement of axial compressive force in the tibiotal

Abstract

Reliable and comparable biomechanical testing of total ankle replacement (TAR) systems can only be accomplished with an accurate standardized simulation of ankle mechanics. Information about the kinetics and forces acting on the tibiotalar joint is vital to developing accurate and comparable simulations. Current simulation models rely on extrapolation of 2D force plate information or on mathematical model predictions to approximate the forces at this joint. The main goal of this project was to design an implantable force sensor to isolate and directly measure the axial compressive force acting on the tibiotalar joint during the gait cycle. The ultra high molecular weight polyethylene (UHMWPE) mobile bearing of the Scandinavian Total Ankle Replacement (STAR) was chosen for modification due to the design’s inherent isolation of the axial compressive force. Initial design has focused on creating a radiopaque fluid force sensor that can give reliable and repeatable force measurements at the tibiotalar joint after implantation. The force sensor can be monitored in vivo using fluoroscopic video methods allowing force measurements during weight bearing movements of the ankle joint. Using this data, 2D pattern recognition techniques can be used to recreate a 3D model of the TAR components and model the ankle kinematics corresponding to the compressive force information. Design is currently in the preliminary, feasibility testing stages. Initial tests support the feasibility of the design, but additional design modification and feasibility tesing are required to optimize and validate the design.