Survivorship of hip prosthesis in primary arthrosis: influence of bilaterality and interoperative time in 45,000 hip prostheses from the Finnish endoprosthesis register.

We studied the influence of bilaterality and interoperative time on survivorship of the hip prosthesis. The material consisted of 45,000 (3,153 bilateral) total hip arthroplasties and 38,000 patients operated on for primary osteoarthrosis, using data from the Finnish Endoprosthesis Register between 1980 and 1999. Cox regression analysis showed that male sex, young age, uncemented prosthesis and time of surgery (first 10-year period) were significant risk factors for aseptic loosening. We found no difference between the survivorship of the first bilateral and that of unilaterals, but second bilaterals survived better than the unilaterals. Bilateral prostheses survived better when the second prosthesis was implanted during the first postoperative year. The risk of loosening of a bilateral prosthesis increased when the second prosthesis was implanted a few years later. Survivorship of bilateral prosthesesin a 1-stage bilateral operation was about the same as in those operated on within the first postoperative year. Better survivorship of the second bilateral can cause bias in per hip survivorship analyses. In bilateral cases, the second hip should be operated on as soon as possible or be considered for a 1-stage bilateral procedure.