Survival of hip replacements. A comparison of a randomized trial and a registry

Abstract

At the authors' hospital, 410 primary total hip replacements were performed on 372 patients between September 1, 1985, and May 31, 1989. All hips were assigned randomly to receive a Charnley prosthesis with an ogee flanged cup or a Spectron prosthesis with a metal backed cup. Eleven-year survivor analysis, using revision as the end point definition of failure, revealed a survival rate of 93.2% +/- 5.8% for the Charnley replacement and 95.9% +/- 3.0% for the Spectron. If each component of the systems was analyzed (concerning aseptic loosening), the ogee cup and the Spectron stem had 100% survival. The survivorship for all 410 hips was 94.5% +/- 3.4%. If the end point definition of failure was expanded to include patient dissatisfaction, the survival rate decreased to 86.3% +/- 4.9%. These survival rates were compared with the rates obtained by the Swedish National Hip Registry. The national cohort included all patients in Sweden who were treated surgically with a Charnley (14,053 patients) or Spectron (metal backed cup) prosthesis (726 patients) between September 1, 1985, and May 31, 1989. Eleven-year survivor analysis revealed a national survival rate of 92.1% +/- 0.7% for the Charnley replacement and 88.6% +/- 6.1% for the Spectron. The analyses from the Swedish Registry are based on more than 160,000 primary operations and 11,500 revisions. Despite the enormous amount of data, there are drawbacks, and registries never can replace the prospective, randomized trial. One reason is the Swedish National Registry is unable to discriminate between the individual cup and stem components when analyzing the cause of revision, and no clinical or radiographic information is collected. A potential drawback for the randomized trial is performance bias because surgeons from specialized centers might perform better than the general orthopaedic surgeon.