The effect of cup orientation and coverage on contact mechanics and range of motion of metal-on-metal hip resurfacing arthroplasty

Implant malpositioning has been identified as a factor associated with clinical failures of metal-on-metal hip resurfacings (MoMHRs). This study investigated the effect of cup orientation and cup coverage on the contact mechanics (incidence of edge-loading) and range of motion (ROM) of MoMHR. Three generic MoMHRs with differing amounts of cup coverage were considered at various orientations. Contact area and contact pressure at the bearing surface were predicted for each design using finite element (FE) method. The ROM was determined based on the geometry overlap. Edge contact was found at lower angles of inclination (65 degrees) for lower coverage cup designs; however, they also provided the greatest ROM. Conversely, cups with greater coverage did not exhibit edge contact until the cup was more steeply positioned (75 degrees), however ROM was reduced. This study enables both sets of variable to be considered in the design of metal-on-metal bearings in hip.