Comparative approach to knee endoprosthesis stem materials - static analysis of bone-implant system by the means of FEM

Abstract

The main aim of this work was evaluation of the displacements, strains and stresses in components of knee endoprosthesis by means of Finite Element Method. The semiconstrained knee endoprosthesis instrumented into femur and tibia bones was chosen for the analysis. The first step was preparation of full knee endoprosthesis geometrical model which was developed on a basis of a real model. Using reverse engineering methods containing 3D scanning and post-processing, model was obtained and then modified due to analysis assumptions. To carry out an analysis it was necessary to develop a femur and tibia bone models, which were obtained from MRI scans. Next a grid for finite-element method calculations was generated for the geometrical model. Mesh was next optimized to obtain high quality elements along with simplification of calculations. Subsequently it was necessary to specify and set the edge conditions to reflect appropriately the phenomena taking place in the real system. The system was loaded with axial force from femur proximal joint surface to tibia distal joint surface in range of 500- 2000N. Calculations were realized for endoprosthesis components made of chromium alloy for femoral joint surface part, UHMWPE for plastic sliding bearing and five different titanium alloys for endoprosthesis femoral part stem and tibial implant part – Table I. On a basis of obtained results, the highest values of reduced stress in endoprosthesis elements were observed in the stems of both femoral and tibial part. Stress in bone didn’t exceed its compression strength for all of chosen materials. The biomechanical analysis may form the basis for improving the geometry of analyzed endoprostheses and optimizing a selection of the mechanical properties of the material used to manufacture them.