Survivorship and Retrieval Analysis of Sikomet Metal-on-Metal Total Hip Replacements at a Mean of Seven Years

Background: Second-generation metal-on-metal total hip replacements were introduced in the early 1990s with the aim of eliminating polyethylene wear and the resulting complications of osteolysis and aseptic loosening. The goal of the present study was to evaluate the intermediate-term results in a series of patients who were managed with one of these implants.

Methods: Between 1994 and 2002, we performed 640 total hip replacements in 591 patients with use of a Bicon-Plus cementless threaded cup with a polyethylene liner housing a metal inlay made of Sikomet low-carbon cobalt-chromium-molybdenum alloy that articulates with a Sikomet metal femoral head. Clinical and radiographic evaluation was performed retrospectively at a mean of 7.1 years postoperatively. Histologic analysis was performed on specimens retrieved from seventeen hips that were revised, and wear measurements were made for six hips that were revised.

Results: Thirty-four hips (thirty-four patients) were revised because of infection (six hips), aseptic loosening (twenty-three hips), pain without loosening (two hips), or other reasons (three hips). The survival rate of the prosthesis as a whole at ten years, with revision for any reason as the end point, was 0.91 (95% confidence interval, 0.88 to 0.95). The survival rate of the cup was 0.94 (95% confidence interval, 0.90 to 0.97), and that of the stem was 0.96 (95% confidence interval, 0.94 to 0.98). Linear or expansile osteolysis, or both, was observed on the radiographs of sixteen (64%) of the twenty-five hips that were revised because of aseptic loosening and/or pain. Histological analysis of pericapsular tissue was performed for seventeen of the twenty-five hips that were revised because of aseptic loosening and/or pain. Thirteen of these seventeen hips demonstrated a hypersensitivity-like reaction with aseptic inflammatory changes accompanied by moderate to extensive diffuse and perivascular infiltration of lymphocytes. In the six retrieved specimens that were subjected to wear analysis, the main wear mode was abrasive wear. The mean cumulative linear wear for the bearing was 31.3 μm, and the mean annual wear rate was 6.3 μm/yr. The mean clearance was 87.6 μm.

Conclusions: After a mean duration of follow-up of seven years, aseptic loosening was the major reason for failure of Sikomet metal-on-metal prostheses. The histological findings and the prevalence of osteolysis suggest the possibility of a hypersensitivity-like immunological response to wear particles.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.