Metal-on-metal vs metal-on-improved polyethylene bearings in total hip arthroplasty

Major weaknesses of total hip arthroplasty (THA) in the 20th century were polyethylene wear and dislocation. Efforts to improve THA took several directions including improvement of polyethylene and use of metal-on-metal (MoM) articulations. Metal-on-metal articulations showed excellent early results, but concerns mount over hypersensitivity and increasing failure. This study compares our experience with MoM and metal-on-improved polyethylene (MoIP) bearings in primary THA. We identified 1362 patients undergoing 1589 MoM THA and 693 patients undergoing 779 MoIP THA (all compression molded and sterilized in argon). Overall, more MoM than MoIP cups have been revised (4.0% vs 2.2%; P = .0241). Revision incidence for infection was similar; higher with MoM for loosening (P = .0020), metal complication (P = .0017), and combined aseptic causes (P = .0067); and higher for dislocation in MoIP (P = .0246). Metal-on-improved polyethylene devices had superior results compared with MoM in this study. Furthermore, 5 MoIP revisions were liner exchanges, a conservative option not available with MoM.