Effects of age and body mass index on the results of transtrochanteric rotational osteotomy for femoral head osteonecrosis: surgical technique.

BACKGROUND

Advanced-stage osteonecrosis and a large area of necrotic bone are known risk factors for failure of transtrochanteric rotational osteotomy of the hip in patients with osteonecrosis. The purpose of this study was to determine whether there are other risk factors for failure of this osteotomy.

METHODS

One hundred and five patients (113 hips) underwent an anterior transtrochanteric rotational osteotomy for the treatment of femoral head osteonecrosis and were followed for a mean of 51.3 months postoperatively. Radiographic failure was defined as secondary collapse or osteoarthritic change. Multivariate analysis was performed to assess factors associated with secondary collapse and osteophyte formation. The Kaplan-Meier product-limit method was used to estimate survival.

RESULTS

Secondary collapse occurred in twenty-seven hips (24%), and fourteen hips (12%) were converted to a total hip arthroplasty. At the time of the most recent follow-up, the hip scores according to the system of Merle d'Aubigné et al. ranged from 6 to 18 points (mean, 15.8 points). Multivariate analysis showed that the stage of the necrosis (III or greater) (hazard ratio = 3.28; 95% confidence interval = 1.49 to 7.24), age of the patient (forty years or older) (hazard ratio = 1.08; 95% confidence interval = 1.02 to 1.14), body mass index (≥24 kg/m(2)) (hazard ratio = 1.19; 95% confidence interval = 1.03 to 1.38), and extent of the necrosis (a combined necrotic angle of ≥230°) (hazard ratio = 1.08; 95% confidence interval = 1.04 to 1.11) were associated with secondary collapse. Seven of the eighty-six hips without collapse showed progression to osteoarthritis. The survival rate at 110 months was 63.4% (95% confidence interval = 51.1% to 75.7%) with total hip arthroplasty or radiographic failure as the end point and 56.0% (95% confidence interval = 44.6% to 67.4%) with total hip arthroplasty, radiographic failure, or loss to follow-up as the end point.

CONCLUSIONS

Our study showed that age, body mass index, and the stage and extent of the osteonecrosis were determining factors for secondary collapse, unsatisfactory clinical results, and conversion to total hip arthroplasty. These factors should be considered when selecting patients for a transtrochanteric rotational osteotomy.