STRUCTURAL ANALYSIS OF A POSTERIOR STABILITY TOTAL KNEE JOINT REPLACEMENT

Abstract

Aim of this work is to compare two different total knee prostheses that differ in the shape of the Polyethylene (PE) insert, trying to optimize the shape of the best one, in order to reduce the stress peaks. The study procedure has been divided into the following steps. First step has been the three-dimensional shape acquisition of the two prostheses by means of a COMET5 3D scanner. The morphology of two prototypes of the prostheses has been acquired by elaborating multiple Moirè fringe pattern projected on their surfaces. Second step consisted of the manipulation of these data in a CAD module, that is the interpolation of raw data into parametric surfaces, reducing singularities due to the typical scattering of the acquiring system. Third step has been the setting up of FEM simulations to evaluate the prostheses behaviour under typical loading conditions. The CAD model of the prostheses has been meshed into solid finite elements. Different flexion angles configurations have been analysed, the load being applied along the femoral axis. FEM analyses have returned stress fields in the PE insert and, in particular, in the stabilizing cam which function is to avoid dislocation. Last step has been the integrated use of CAD-FEM to modify the shape of the stabilizing cam of the best prosthesis, in order to reduce the stress peaks in the original prosthesis without compromising the kinematics of the joint. Good results have been obtained both in terms of stress and contact pressure peaks reduction.