How much varus is optimal with proximal femoral osteotomy to preserve the femoral head in Legg-Calvé-Perthes disease?

Background: Although proximal femoral varus osteotomy is an established operative treatment for Legg-Calvé-Perthes disease, there is a lack of data on how much varus at the osteotomy is optimal for preserving the spherical shape of the femoral head. The purpose of this study was to determine if there is a correlation between the amount of varus used and the Stulberg radiographic outcome at maturity and to determine if the varus angulation improved over time. Methods: The database and the radiographs of fifty-two patients treated with proximal femoral varus osteotomy from a multicenter prospective study were analyzed. The neck-shaft angles were measured before the operation, after the operation, and at the time of final follow-up, and the amount of varus placed was correlated with the Stulberg outcome at skeletal maturity. Spearman correlations and logistic regression were used for statistical analysis. Results: All patients were six years of age or older at the time of diagnosis (mean 8.0 ± 1.4 years), and all were skeletally mature at the time of follow-up (mean age [and standard deviation] at the time of follow-up, 16.5 ± 2.0 years). The mean neck-shaft angle was 138° ± 7° preoperatively and 115° ± 11° postoperatively with a mean varus change of 23° ± 10°. No significant correlation was observed between the postoperative neck-shaft angle at maturity and the Stulberg outcome (r = -0.15, p = 0.17) and between the amount of varus placed and the Stulberg outcome (r = 0.14, p = 0.36). However, when the lateral pillar groups were analyzed separately with use of logistic regression, a significant relationship was observed for the lateral pillar group B (p = 0.025), with a higher postoperative neck-shaft angle having a greater probability of being associated with a Stulberg class-I or II outcome. At maturity, the mean neck-shaft angle had improved from 115° ± 11° following the initial surgery to 124° ± 8°. However, nineteen (37%) of the fifty-two patients showed no improvement (defined as a change of >5°) and fifteen (29%) of the fifty-two patients had an overriding greater trochanter. Conclusions: Contrary to the conventional belief, greater varus angulation does not necessarily produce better preservation of the femoral head following proximal femoral varus osteotomy. Given the results, our recommendation is to achieve 10° to 15° of varus correction when performing proximal femoral varus osteotomy on hips that are in the early stages of Legg-Calvé-Perthes disease. Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.