Outcome of the modified Dunn procedure in severe slipped capital femoral epiphysis

BACKGROUND: The modified Dunn procedure has rapidly gained popularity as a treatment for slipped capital femoral epiphysis (SCFE) during the past few years. However, there is limited information regarding its safety and efficacy in severe slips with this procedure. The purpose of this study is to present clinical results and incidence of complications associated with the modified Dunn osteotomy in a consecutive series of severe SCFE cohort. PATIENTS AND METHODS: We retrospectively assessed the outcomes of all twenty patients who had been treated with the modified Dunn procedure in our tertiary-care institution. According to the Loder and Fahey criteria, all cases were classified as severe slips; nineteen cases were stable, and one case was an unstable slip. All surgical procedures were performed by one senior orthopedic surgeon who had specific training in the modified Dunn procedure. Operative reports, outpatient records, follow-up radiographs, and the intraoperative findings were reviewed to determine the demographic information, type of fixation, final slip angle, presence of avascular necrosis (AVN), and any additional complications. The mean age of the patients was 13.2 ± 1.6 years (range, 10 to 17 years). Twenty patients (twenty-one hips) with a mean of 31.2 ± 14 months (range, 12 to 57 months) follow-up met the inclusion criteria. Pain and function were assessed by the modified Harris score and WOMAC score. Radiographic anatomy was measured using the slip angle and α-angle. The radiographic findings related to the anatomy of the femoral head-neck junction, as well as signs of early-onset of osteoarthritis (OA) and AVN, were evaluated pre- and postoperatively. RESULTS: Overall, nineteen patients had excellent clinical and radiographic outcomes with respect to hip function and radiographic parameters. One patient (5%) who developed implant failure at 3 months postoperatively had a poor outcome. The mean preoperative slip angle was corrected from 63.2 ± 8.1° (range, 51 to 84°) to a normal value of 7.5 ± 3.5° (range, 2 to 15°) (p < 0.01). The mean α-angle was improved from an average of 94.5 ± 21.1° (range, 61 to 123°) to postoperative 42 ± 6.4° (range, 25 to 55°) (p < 0.01). The mean modified Harris hip and WOMAC scores postoperatively were 96.7 ± 13.4 (range, 40 to 100) and 95.4 ± 10.6 (range, 38 to 100), respectively. There were no cases of the development of femoroacetabular impingement (FAI) and the progression of OA. We did not record any case of AVN, closure of the growth plate, heterotopic ossification (HO), trochanteric nonunion, or limb length discrepancy that occurred postoperatively either at the most recent follow-up. CONCLUSIONS: Our series of severe SCFEs treated with the modified Dunn osteotomy demonstrated that the procedure is safe and capable of restoring more normal proximal femoral anatomy by maximum correction of the slip angle, minimizing probability of secondary FAI and early onset of OA. However, despite its lower surgical complication rate compared with alternative treatment described in the literature for SCFE, AVN can and do occur postoperatively which should always be concerned in every hip.