Treatment of Unstable Versus Stable Slipped Capital Femoral Epiphysis Using the Modified Dunn Procedure.

BACKGROUND: The modified Dunn procedure (open subcapital realignment via a surgical dislocation approach) has been shown to be a safe and effective way of treating acute, unstable slipped capital femoral epiphysis (SCFE). There is a paucity of literature comparing the modified Dunn procedure in stable SCFE. The purpose of this study was to compare acute, unstable versus chronic, stable SCFE managed with the modified Dunn procedure.

METHODS: A retrospective chart review was performed on 44 skeletally immature patients who underwent the modified Dunn procedure for SCFE. Patients were divided into stable or unstable based on clinical presentation and intraoperative findings. Demographics, radiographic measurements, and complications were recorded and compared. χ and t tests were used to compare variables.

RESULTS: In total, 31 consecutive hips (29 patients) with acute, unstable slips, and 17 consecutive hips (15 patients) with chronic, stable slips were reviewed. Average age was 12.5 and 13.8 years for acute and chronic, respectively (P=0.05). Mean follow-up was 27.9 months (unstable) and 35.5 months (stable). Average postoperative Southwick angle was 14.2 degrees; (unstable) and 25.3 degrees (stable) (P=0.001). Greater trochanteric height averaged 6.2 mm below the center of the femoral head in the acute group and 6.2 mm above center in the chronic group (P<0.001). Average femoral neck length measured 34.1 mm (unstable) and 27.1 mm (stable) (P<0.001). Two patients (6%) developed avascular necrosis (AVN) in the unstable group, with 5 patients (29.4%) in the stable group (P=0.027). All patients with hip instability (N=3) developed AVN.

CONCLUSIONS: Although both acute, unstable and chronic, stable SCFE can be successfully treated with the modified Dunn procedure, the complication rate is statistically higher in patients with stable SCFE, specifically both AVN rate and postoperative instability. In addition, it is more difficult to establish normal anatomic indexes with regard to greater trochanteric height and femoral neck length. This procedure has great utility in the correction of the anatomic deformity associated with SCFE, but should be used with caution in patients with chronic, stable SCFE.

LEVEL OF EVIDENCE: Level III-retrospective review.