Effect of acetabular orientation on stress distribution of highly cross-linked polyethylene liners

Several case reports have documented the fracture of highly cross-linked polyethylene (HCLPE) liners used in total hip arthroplasty (THA). Although uncommon, fractured liners result in considerable morbidity for patients and require revision surgery. One postulated mechanism that leads to this type of implant failure is malorientation of the acetabular component. The purpose of this study was to investigate the effect of acetabular orientation on the stress distribution of HCLPE liners used in THA by means of finite element analysis. Three-dimensional models of a commonly used HCLPE liner were created corresponding to 12 different acetabular component orientations (inclination ranging from 20° to 70° and version ranging from 20° of retroversion to 40° of anteversion). A static stress analysis of the finite element models was performed under conditions simulating peak gait loads. The results of the analysis revealed that excessive inclination and extremes of version were associated with an increase in peak stress magnitudes. The locations of peak stress also were found to lie within the rim notch and locking ring groove regions, which were consistent with the fracture locations reported in published case reports. Therefore, the acetabular component should be oriented carefully during implantation to reduce the risk of rim loading and subsequent liner fracture. In addition, an alternative liner design may further help reduce stress risers and risk of fracture.