SUPERIOR SURFACE FINISHING OF SURGICAL GRADE CHROMIUM COBALT MOLYBDENUM KNEE IMPLANTS

Abstract

It is well established in the literature that the tribological properties of sliding metallic and ultra-high molecular weight polyethylene (UHMWPE) counterfaces are a major contributor to accelerate wear rates that contribute to osteolysis. The majority of the research over the years has been on improving the UHMWPE properties through manufacture and secondary processing of the polymer. Little attention has been directed towards the optimisation of the Chromium Cobalt Molybdenum (CrCoMo) surface finish.

The focus of this research has been on the highly polished CrCoMo metallic surface. A new surface finishing technique was applied to CrCoMo femoral knee prosthetic implants. The surface finish of our finished implants was compared to that finished by traditional mechanical polishing techniques. A representative number of polished CrCoMo knee femoral components were compared under the following topics; tribological, topographical and the extent of processing containments present.

It was found that traditional mechanically polished parts contained a significant amount of embedded polishing compounds (Al2O3), coarse interdendritic (M7C3) and fine (M23C6) carbide elements. Both the polishing containments and carbide elements stand proud of the articulating surface and thus act as micro cutting tools to accelerate UHMWPE wear. The new polishing technique completely eliminated hard carbide particles and embedded polishing compound media. Consequently, the samples prepared using the new polishing technique produced lower UHMWPE wear debris and improved wear patterns to that of the traditionally polished samples. Additionally, all sub-micron scratching was removed from the surface of the samples.

This polishing technique for CrCoMo prosthesis represents a milestone in CrCoMo surface finishing and will significantly reduce the UHMWPE wear debris generated and consequently increasing prosthesis longetivity.