Overestimation of the risk of revision with Kaplan-Meier presenting the long-term outcome of total hip replacement in older patients.

INTRODUCTION: The purpose of the present study was (i) to review the long-term outcome of cemented Charnley total hip replacements (THRs) performed by 1 surgeon (GH), 20 to 42 years ago, in patients ≥60 years, using both the Kaplan-Meier (KM) and the cumulative incidence (CI) methods, and (ii) to compare the estimations of the 2 statistical methods.

METHODS: We evaluated the outcome of 306 consecutive primary cemented THRs that were performed in 265 patients. The final clinical, radiographic assessment and satisfaction of living patients were also included. The survivorship was estimated with the use of KM and CI methods and the relative difference between their estimations was calculated.

RESULTS: Living patients' final clinical results were significantly improved in comparison with respective preoperative ones, and all the acetabular and 91% of femoral components considered as well fixed. 95% of these patients reported satisfaction. The risk of revision at 25 years, with revision for aseptic loosening for 1 or both components as the endpoint, with 21 hips at risk, assessed with KM analysis was 6.9% and with CI approach was 3.9%. The relative difference between KM and CI estimations was increasing during follow-up, reaching up to 76.8% at 25 years.

CONCLUSIONS: We concluded that fixation of implants with cement in older patients had satisfactory long-term results and can serve as a benchmark with which to compare newer fixation methods (hybrid and uncemented) and materials. However, KM method, in studies that include older population with long-term follow-up, may significantly overestimate the risk of revision and clinicians could consider using besides the cumulative incidence of competing risk method.