Background: Deformity of the femoral head after open reduction for developmental dislocation of the hip (DDH) influences the outcome of pelvic osteotomy as a final correction for residual dysplasia to prevent secondary osteoarthritis. The purpose of this study was to review long-term outcomes after open reduction using a medial approach for DDH. The correlation between age at the time of operation and femoral head deformity at skeletal maturity was specifically evaluated.

Methods: Forty-two hips in 40 patients with more than 10 years of follow-up were assessed radiologically. The mean age at the time of surgery was 14.3 (range, 6–31) months, and the postoperative follow-up period ranged from 10 to 27 (mean, 15.8) years. The round and enlargement indices of the femoral head were measured on follow-up radiographs to evaluate deformity and enlargement of the femoral head at skeletal maturity.

Results: Severin classification was I and II in 16 hips; III, IV, and V in 23; and II at the final follow-up in the 3 hips treated by osteotomy less than 10 years after open reduction. Mean round index at follow-up was 58.3 ± 8.3 (range, 47–79); it showed correlation with age at the time of operation (r = 0.68, p < 0.001). Mean enlargement index at follow-up was 113.4 ± 11.8 (range, 93–137) and showed no correlation with age at the time of operation (r = 0.009, p = 0.96).

Conclusions: At more than 10 years’ follow-up, the occurrence of deformity of the femoral head correlated with increased age at the time of operation. Indications for use of a medial approach in the correction of DDH in older patients must take into account the risk of subsequent femoral head deformity at skeletal maturity.