Long-term results of the modified Dunn procedure in slipped capital femoral epiphysis : a minimum of ten-year follow-up.

AIMS: In situ fixation for slipped capital femoral epiphysis (SCFE) prevents further displacement, but fails to correct the proximal femoral deformity, which may lead to femoroacetabular impingement (FAI) and early osteoarthritis (OA). The modified Dunn procedure (MDP) restores proximal femoral anatomy with the aim of improving long-term joint preservation. However, evidence beyond mid-term follow-up remains limited. This study evaluates the ten-year survivorship, functional outcomes, and radiological correction following MDP. METHODS: A retrospective single-centre review was performed of patients treated with the MDP between 2007 and 2014 for stable or unstable SCFE of any severity. Patients with preoperative avascular necrosis (AVN) were excluded. Primary outcomes were ten-year survivorship free from conversion to total hip arthroplasty (THA) and from radiological OA progression (≥ 1 Tönnis grade). Secondary outcomes included patient-reported outcome measures, hip range of motion, clinical signs of FAI, and correction of the Southwick and α angles. Kaplan-Meier survival analyses were performed and stratified by slip severity. RESULTS: A total of 35 hips (34 patients) completed ≥ ten years of follow-up (163 months (SD 34)). Ten-year THA conversion-free survivorship was 88.6%, decreasing from 100% in mild slips to 86.4% in moderate and 83.3% in severe slips. Ten-year OA progression-free survivorship was 82.9%, with rates of 100%, 81.8%, and 66.7% for mild, moderate, and severe slips, respectively. The mean ten-year functional scores were high (modified Harris Hip Score 88.9 (SD 4.4); University of California, Los Angeles Activity Scale 8.9 (SD 1.6); and Merle d'Aubigné-Postel 17.7 (SD 0.9)). Substantial radiological correction was observed, with the Southwick angle improving from 45.0° to 13.1° and the α angle from 85.8° to 50.9°. No postoperative AVN occurred. CONCLUSION: At ten-year follow-up, the MDP achieved excellent functional outcomes and effective deformity correction in SCFE, with high survivorship in mild and moderate slips. However, progression of hip OA was less favourable in severe slips.