Elastohydrodynamic lubrication analysis of metal-on-metal hip implants with complex structures using the finite-element method

Various complex structures are employed in different metal-on-metal (MOM) hip prostheses for different purposes. For the elastohydrodynamic lubrication (EHL) study of these prostheses, the elastic deformation calculation is not a trivial task due to the effect of complex structures. The finite-element method (FEM) is an attractive approach for solving these problems because of its flexibility in handling complex geometries. Moreover, the availability of high-level ready-to-use finite-element commercial software may facilitate the modelling of complex structures and thereby reduce the time spent on implementing the analysis. In this study, a numerical method was developed to solve the EHL problems of MOM hip prostheses with complex structures. In this method, the elastic deformation was calculated from the product of the flexibility matrix of the lubrication nodes and the nodal force. The flexibility matrix was obtained by inverting the stiffness matrix, which was obtained through finite-element analysis using commercial software. The nodal force was obtained by transferring the hydrodynamic pressure according to the isoparametric element definition. This method was validated for a typical 28 mm diameter MOM total hip replacement. The effects of the structures of the femoral head, the wall thickness of the cup, as well as the bone quality of patients on lubrication performance of MOM hip resurfacing prostheses were subsequently investigated.