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

Abstract

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.

Predictive wear modeling of the articulating metal-on-metal hip replacements

“…A significant amount of research has been undertaken on the EHL of artificial hip joints . In these models, the interaction of the fluid film pressure and the elastically deformable head and cup is calculated to predict both the film thickness and the lubricating fluid pressure.…”

“…A significant amount of research has been undertaken on the EHL of artificial hip joints. [1][2][3][4][5][6][7][8][9][10][11][12][13] In these models, the interaction of the fluid film pressure and the elastically deformable head and cup is calculated to predict both the film thickness and the lubricating fluid pressure. Such studies have shown that the fluid-filled lubricating gap is at nanometer size-an extremely small gap when compared to typical engineering bearing problems, where the fluid-filled gap is typically in a range of 1-100 mm.…”

Effect of simplifications of bone and components inclination on the elastohydrodynamic lubrication modeling of metal-on-metal hip resurfacing prosthesis

“…The diameter, radial clearance and cup thickness of this surface hip prosthesis were 50 mm, 75 mm and 3.94 mm, respectively. 23 The minimum and maximum thicknesses of the head were 2.5 and 9 mm, respectively. The radius and length of the pin of the head were approximately 3.5 and 60 mm, respectively.…”

“…19 The current EHL models applicable to hip replacements can be found in a few review articles. 19,20 Although a large number of lubrication studies have been performed for THRs, 20 only few studies [21][22][23] have been performed to investigate how design parameters, such as the head diameter, diametric clearance, cup wall thickness and detailed structures and fixation of the femoral component, affect the EHL of MOM hip resurfacing prostheses. These studies assumed that the cup was horizontally positioned and the head was vertically positioned.…”

“…[24][25][26][27][28][29] Moreover, in these studies, the pelvis and femur were simplified using equivalent bone models with appropriate material properties. [21][22][23] Although a contact mechanics study has been performed to justify the application of the equivalent bone models, 22 the effects of realistic bone structures on the lubrication performance of MOM hip resurfacing prostheses remain unknown due to the lack of a full model that considers the realistic geometries and material properties of the pelvis and femur.…”