Contact mechanics and elastohydrodynamic lubrication in a novel metal-on-metal hip implant with an aspherical bearing surface

Abstract

Diameter and diametral clearance of the bearing surfaces of metal-on-metal hip implants and structural supports have been recognized as key factors to reduce the dry contact and hydrodynamic pressure and improve lubrication performance. On the other hand, application of aspherical bearing surfaces can also significantly affect the contact mechanics and lubrication performance by changing the radius of the curvature of a bearing surface and consequently improving the conformity between the head and the cup. In this study, a novel metal-on-metal hip implant employing a specific aspherical bearing surface, Alpharabola, as the acetabular surface was investigated for both contact mechanics and elastohydrodynamic lubrication under steady state conditions. When compared with conventional spherical bearing surfaces, a more uniform pressure distribution and a thicker lubricant film thickness within the loaded conjunction were predicted for this novel Alpharabola hip implant. The effects of the geometric parameters of this novel acetabular surface on the pressure distribution and lubricant thickness were investigated. A significant increase in the predicted lubricant film thickness and a significant decrease in the dry contact and hydrodynamic pressures were found with appropriate combinations of these geometric parameters, compared with the spherical bearing surface.

Tribology of artificial joints

“…The drive to preserve bone on the acetabular side of large diameter bearings has led to thinner components that may deform elastically when implanted, leaving a non-spherical component. 16 Whether the bone relaxes around this implant, allowing it to go back to its original shape or not, remains to be seen. However, if the clearance is small the change in shape due to implantation may be significant enough, at least in the short term, to cause circumferential impingement.…”

Do Ion Levels In Hip Resurfacing Differ From Metal-on-metal THA at Midterm?

“…For this reason, the introduction of large-diameter MOM bearings, as used in MOM-BHR, has prompted even more concern [5]. However, the large diameter and low radial clearance of MOM bearings are key factors in reducing dry contact and hydrodynamic pressures and important in improving lubrication performance [25]. The better lubrication regime observed with large-diameter MOM bearings with low clearance allows for a thicker fluid film which completely separates the articular surfaces, generating less wear [22,35].…”

Prediction of contact mechanics in metal-on-metal Total Hip Replacement for parametrically comprehensive designs and loads

“…Previous researchers have observed individual contact categories including normal-polar (Besong et al, 2001;Cosmi et al, 2006;Jagatia and Jin, 2002;Liu et al, 2003Liu et al, , 2008Mak et al, 2011;Meng et al, 2010;Sariali et al, 2012;Udofia et al, 2004;Wang et al, 2014;Yew et al, 2003), ring-polar (Besong et al, 2001;Cosmi et al, 2006;Jagatia and Jin, 2002;Liu et al, 2003Liu et al, , 2004Meng et al, 2010;Udofia et al, 2004;Yew et al, 2003), asymmetric-polar (Besong et al, 2001), transitional-polar (Elkins et al, 2012;Mak et al, 2011;Sariali et al, 2012;Wang et al, 2014), transitional-edge (Elkins et al, 2012;Sariali et al, 2012) and normal-edge (Elkins et al, 2012;Sariali et al, 2012;Wang et al, 2014). The present study included all categories and facilitated a comprehensive understanding of their multi-factorial causes .…”

“…Most previous analyses have focused on polar loading (Besong et al, 2001;Bevill et al, 2005;Cosmi et al, 2006;Fialho et al, 2007;Jagatia and Jin, 2002;Liu et al, 2011Liu et al, , 2003Liu et al, , 2008Maxian et al, 1996;Meng et al, 2010;Udofia et al, 2004;Yew et al, 2003), with some recent attention to edge loading (Elkins et al, 2012(Elkins et al, , 2013Mak et al, 2011;Sariali et al, 2012;Wang et al, 2014); the latter associated with subluxation, head-on-rim contact, and extreme wear in explant analyses (Al-Hajjar et al, 2013;Currier et al, 2013). However, continuous solutions for contact mechanics and permanent deformation throughout transition from polar through near-edge to edge loading have not been reported.…”