METAL BACKED ACETABULAR CUPS WITH CONVENTIONAL POLYETHYLENE. A REVIEW OF 9113 PRIMARY ACETABULAR CUPS WITH 0–20 YEARS FOLLOW-UP FROM THE NORWEGIAN ARTHROPLASTY REGISTER

Abstract

Background: In the Norwegian Arthroplasty Register several uncemented femoral stems have proved good or excellent survivorship. The overall results of uncemented total hip arthroplasty however, have been disappointing due to inferior results of the metal backed acetabular cups. In this study we investigated the medium-term performance of primary uncemented metal backed acetabular cups exclusively.

Methods: 9 113 primary uncemented acetabular cups in 7 937 patients operated in the period 1987–2007 were included in a prospective, population-based observational study. All were modular, metal-backed uncemented cups with ultra-high molecular weight polyethylene liners and femoral heads made of steel, cobalt chrome, or Alumina ceramics. Thus 7 different cup designs were evaluated with the Kaplan-Meier method and Cox regression analyses.

Results: Most cups performed well up to 7 years. When the end-point was cup revision due to aseptic cup loosening, the cups had a survival of 87 to 100% at 10 years. However, when the end-point was cup revision of any reason, the survival estimates were 81 to 92% for the same cups at 10 years. Aseptic loosening, wear, osteolysis and dislocation were the main reasons for the relatively poor overall performance of the metal backed cups in this study. Prostheses with Alumina heads performed slightly better than those with steel- or cobalt chrome in sub-groups.

Conclusions: Whereas most cups performed well at 7 years, the survivorship declined with longer follow-up time. Fixation was generally good. None of the metal-backed uncemented acetabular cups with UHMWPE liners investigated in the present study had satisfactory long-term results due to high rates of wear, osteolysis, aseptic loosening and dislocation. Hopefully cross-linked liner inserts will improve long term outcome in the future.