Survivorship analysis of surgical treatment of the hip in young patients.

Survivorship analysis has become the standard statistical technique for evaluating the results of total joint arthroplasty. There are several problems associated with survivorship analysis as it is presented in the orthopaedic literature that apply to younger and older patients. Studies conducted within the same institution using the same prosthesis have reported differences between young and old patients as high as 30% whereas other studies have reported differences as low as 2%. When discrepancies such as this exist it is clear that more care is needed when presenting results and making comparisons among younger patients. The major reason for the higher revision rates in younger patients usually has been an assumption of higher patient activity resulting in more wear for the prosthesis. However, some older patients are very active after surgery and some younger patients are very inactive. I will discuss the need for more sophisticated instruments measuring patient activity and statistical procedures that are necessary for the proper presentation of data involving younger patients. The statistical issues include the need for multivariate survival analysis and the need for time varying measurements of patient activity.