Medium-term outcome of periacetabular osteotomy and predictors of conversion to total hip replacement.

BACKGROUND Little is known about medium or long-term results of periacetabular osteotomy and which factors predict a poor outcome in terms of conversion to total hip replacement. The aims of this study were to assess the medium-term outcome following periacetabular osteotomy and to analyze what radiographic and patient-related factors predict a poor outcome. METHODS One hundred and sixteen periacetabular osteotomies performed by the senior author from December 1998 to December 2002 were eligible for inclusion. Data were assessed through database inquiry and evaluation of radiographic material. The mean duration of follow-up was 6.8 years. At the time of follow-up, we conducted an interview, performed clinical and radiographic examinations, and asked the patients to complete the Western Ontario and McMaster Universities Osteoarthritis Index and the Short Form-36 questionnaires. We performed a Kaplan-Meier survival analysis, and we used a Cox proportional hazards model to identify factors predicting a poor outcome. RESULTS With conversion to total hip replacement as the end point, the Kaplan-Meier analysis showed a hip survival rate of 81.6% (95% confidence interval, 69.7% to 89.3%) at 9.2 years. At the time of follow-up, the median physical component score on the Short Form-36 was 48.31, the median mental component score on the Short Form-36 was 57.95, and the median Western Ontario and McMaster Universities Osteoarthritis Index total score was 84.44. The median pain score on the visual analog scale was 0 at rest and 1 after fifteen minutes of normal walking. When adjusting for preoperative osteoarthritis, we identified seven factors predicting conversion to total hip replacement. Preoperative predictive factors were severe dysplasia on conventional radiographs and computed tomographic scans, reduced acetabular anteversion angle on computed tomographic scans, and the presence of an os acetabuli (calcification of a detached labrum). Predictive factors identified on the immediate postoperative radiographs were a small width of the acetabular sclerotic zone and excessive lateral and proximal dislocation. CONCLUSIONS Periacetabular osteotomy can be performed with a good outcome at medium-term follow-up, suggesting that it may be applied by experienced surgeons with satisfactory results. To further improve the outcome, focus should be on the potential negative influence of parameters that are easily assessed, such as the preoperative grade of osteoarthritis, the presence of an os acetabuli, and severe acetabular dysplasia.