The effect of polymerization of methylmethacrylate on metal-backed and non-metal-backed acetabular components.

Aseptic loosening of the acetabular component has been identified as the main cause of failure of cemented total hip arthroplasty in the long term. Wear of the high-density polyethylene has been implicated as a major contributory factor to loosening. The etiology of wear is multifactorial. The exothermic phase of polymerization of polymethylmethacrylate is associated with a 5.9% volume expansion. Using double-exposure holographic interferometry, the authors examined the influence of polymerization of cement on the internal geometry of a metal-backed cup and two non-metal-backed cups (Charnley 22 mm, Muller 32 mm). The non-metal-backed cups exhibited marked heat concentration points and disrupted fringe patterns, indicating distortion of the internal geometry of the cup. In contradistinction, the metal-backed cup showed good heat dissipation and regular fringe patterns, indicating minimal internal distortion. The differences were not quantified but were visually dramatic. The authors believe this may be an important contributory factor to cup wear in cemented total hip arthroplasty.