Evaluation of the gluteus medius muscle after a pelvic support osteotomy to treat congenital dislocation of the hip

Background: Many authors have reported that the pelvic support osteotomy prevents a Trendelenburg gait by restoring the biomechanics of the abductor muscle in patients with congenital dislocation of the hip. However, we are not aware of any studies in which the hip abductor muscles were examined following pelvic support osteotomy. The purpose of this study was, first, to use magnetic resonance imaging to measure alterations in the length and volume of the gluteus medius muscle after pelvic support osteotomy and, second, to determine which factors influence the results of the Trendelenburg test. Methods: Eleven patients with a history of congenital hip dislocation who had been treated with a pelvic support osteotomy were examined clinically with the Harris hip score and the Trendelenburg test, radiographically to measure limb-length discrepancy and valgus angulation of the proximal part of the femur, and with magnetic resonance imaging to measure changes in the gluteus medius length and volume. Results: The pelvic support osteotomy achieved a functional and painless hip in all eleven patients. Five of the eleven patients had a persistently positive Trendelenburg gait at the time of the last follow-up visit, at an average of three years after the osteotomy. The muscle volumes were restored to 43% to 89% of the muscle volumes on the normal contralateral side, and the postoperative muscle volume correlated significantly with the result of the Trendelenburg test (r = -0.63; p = 0.03). There was a positive association between age and the result of the Trendelenburg test (p = 0.01): four of the five patients who had a positive test were at least thirty-one years of age at the time of the operation. There was no correlation between the Trendelenburg test and the change in the length of the gluteus medius muscle, which averaged 19.2 mm in the patients with a positive test and 19.3 mm in those with a negative test. Conclusions: Patient age at the time of the operation and the postoperative change in the volume of the gluteus medius muscle have a significant influence on the result of the Trendelenburg test after a pelvic support osteotomy. Moreover, our study demonstrated that restoration of the muscle volume after a pelvic support osteotomy is not sufficient to prevent a Trendelenburg gait in older patients with congenital dislocation of the hip.