Considerations in the comparison of cemented and cementless total hip prostheses.

Based on conservative models of the revision rates for cemented and uncemented hip arthroplasties, the required number of patients for a study to show significant uncemented superiority was determined using standard statistical techniques. A review of the literature was done to ascertain the revision rates for cemented total hip arthroplasties. Patients with osteoarthritis who were older than 50 years had an average revision rate of 1% per year, while those younger than 50 years had revision rates in excess of 2% per year. Specific conditions of the hip were also associated with increased failure rates, most notably the implantation of a revision arthroplasty for a previously failed total hip arthroplasty. Assuming that the uncemented hip had a long-term revision rate of 0.5% per year and an early lack of biologic fixation in 1% of patients, it was found that a 5-year study would have to include at least 2,800 patients (1,400 in each group) if the study population had a cemented failure rate of 1% per year and a total of 230 patients in those having a cemented failure rate of 2% per year. The patients needed for a 10-year evaluation would be 700 and less than 100, respectively. Altering the long- or short-term revision rate for uncemented total hip arthroplasty had relatively little effect on the study size. This analysis indicates that a comparison study would be best done in patients who have high failure rates with cemented total hip arthroplasties. Multicenter trials involving younger patients or those undergoing revision surgery are ideally suited for such an investigation.