SURFACE TREATMENTS FOR WEAR MINIMIZATION IN A NEW DESIGN OF TOTAL KNEE REPLACEMENT

Abstract

Design and materials selection and optimisation are the-factors affecting the performance of the modern TKR. In this study new surface treatments were performed and investigated on CoCrMo with the goal to minimize the wear in a new total knee prosthesis design.

Three surface finishing treatments were considered and applied to cast CoCrMo alloy specimens. A surface polishing treatment performed by mass finishing technique was applied on machined CoCrMo. ACoCrMo coating, obtained by Magnetron Sputtering Physical Vapour Deposition (PVD) technique, was applied on mass finished CoCrMo specimens. Conventional hand polishing performed by silicon carbide papers followed by a final diamond past polishing was considered as reference material. For this study not cross-linked not sterilized UHMWPE was used. Surface morphology obtained by the surface treatments was investigated by SEM, Atomic Force Microscopy, and non contact laser profilometry. The microstructure and micro-hardness of CoCrMo alloy was investigated as well. Wear tests were performed in bovine serum using two screening wear test machines. A final wear test was performed on the new knee pros-thesis design using a knee wear simulator, up to five millions cycles.

CoCrMo PVD coating performed on CoCrMo substrate was capable to eliminate and to fill all the surface defects originated by the casting process of the CoCrMo alloy. Such surface defects could not be eliminated by hand polishing or mass finishing process alone. Vickers micro-hardness was improved by the mass finishing treatment. Although the roughness measured on the mass finished specimens was not the lowest, screening wear test produced for them the best results. Wear simulator test performed on the mass finished knee femoral prostheses sliding against UHMWPE, confirmed very low UHMWPE wear generation.

The mass finishing surface treatment applied to cast CoCrMo alloy specimens and femoral components is capable to polish the surface to the level required by standards. The PVD coating investigated was capable to improve the surface morphology of the alloy and to eliminate all the surface micro defects. Nevertheless, the screening wear tests indicated that the mass finishing treatment generate the lowest wear. The results were confirmed by wear simulator test. This study indicated that the mass finishing surface treatment can be effectively applied for the polishing of the femoral components of knee prosthesis.