A Tribological assessment of the porous coated anatomic total hip replacement

Abstract

The tribological performance of internal joint prostheses is a fundamental influence on their longevity. The aim of this study is to characterise the tribological performance of the Porous Coated Anatomic total hip replacement by the analysis of 119 explanted prostheses. Investigations of the friction, wear, surface topography and wear debris were made and related to the joint's clinical performance. The friction of the joints at explant was similar to that of new prostheses. The median total wear volume (419mm(^3)) was found to agree with previous wear studies suggesting the existence of a threshold wear volume which promotes osteolysis. Clinical wear factor for the whole cohort matched that of alternative joint designs. The femoral head finish was shown to degrade but not in proportion to implant duration. The roughness of the UHMWPE liner was shown to fall but no relationship with any head roughness, or temporal, parameter could be distinguished. Simulator studies confirmed that the wear factor of a joint is likely to change over its lifespan. Wear models published previously describing the influence of femoral head roughness on wear could not predict the performance of explanted prostheses. An alternative relationship was observed indicating that head roughness is not as powerful a predictor of wear as previously held. A novel technique for the characterisation of the size distribution of ex vivo and in vitro wear debris was developed. A Low-Angle Laser Light Scattering Particle Analyser was used to size particles continuously over a range from 0.5 to 1000μm. This technique offers considerable unprovement over existing microscope-based methods in terms of the detail of the information and does so with less experimental effort. It was shown to be highly accurate and repeatable in preliminary investigations. Case studies of five tissue samples revealed the potential of this method.