Effect of Acetabular Cup Design on the Tribology of Metal-on-Metal Hip Resurfacing Replacements: A Contact Mechanics and Elastohydrodynamic Lubrication Study

The tribology of metal-on-metal (MOM) hip resurfacing prostheses has been investigated in this study, with particular consideration of the effect of prosthesis design (cup wall thickness and clearance) on the contact mechanics and elastohydrodynamic lubrication (EHL) of these man-made bearings. Two commercially available MOM hip resurfacings, which differ mainly in cup-wall thickness and diametral clearance, were investigated. Finite element contact mechanics and lubrication analyses were carried out on the two MOM hip resurfacing designs. It was found that the thinner acetabular cup with a the relatively smaller clearance resulted in lower contact and hydrodynamic pressure predictions, and a significant increase in the predicted lubricant film thickness at the bearing surfaces. This was attributed to the increase in contact area, conformity between the cup and ball and to the increased influence of the underlying non-metallic structures such as bone and cement, which enhanced the elasticity of the thin acetabular cup. It was shown that full fluid-film lubrication was possible in MOM hip resurfacings during the walking cycle with the small clearance and thin cup-wall thickness model. The importance of the design and manufacturing parameters on the tribological performance of MOM hip resurfacings is highlighted in this study, particularly in promoting fluid film lubrication as a means to further reduce wear at the bearing surfaces.