Is Subcapital Realignment for Slipped Capital Femoral Epiphysis a Reproducible Technique? Midterm Results
Authors: Rego Paulo , Mafra Inês , Viegas Rui , Canhoto Joana , Oliveira Filipe , Pinto Pedro 
Published: January 2024

Background
The modified Dunn procedure, which is based on the development of an extended retinacular flap containing the blood supply for the femoral head, allows anatomic reestablishment in patients with moderate to severe slipped capital femoral epiphysis (SCFE). Some controversy exists regarding the short-term to midterm risk of avascular necrosis (AVN) and other complications resulting from the surgical technique.

Questions/purposes
(1) What percentage of patients treated with an extended retinacular flap during the modified Dunn procedure for SCFE with a moderate (slip angle from 30° to 60°) or severe slip (slip angle equal or greater than 60°) develop symptomatic AVN, and what percentage underwent further surgery or had other complications? (2) What femoral head-neck alignment and position parameters relative to the greater trochanter are achieved after surgery? (3) Can we identify radiographic signs of osteoarthritis at a minimum of 4 years after surgery?

Methods
Between January 2006 and December 2018, we treated 61 patients for SCFE. During this time, we generally used the modified Dunn procedure when the slip angle was ≥ 30°. Based on this indication, the modified Dunn procedure was performed in 37 patients (41 hips) during that time period, and those patients were potentially eligible for this retrospective study. Because bilateral hips in the same patient are not statistically independent, for our analyses, we analyzed only the hip with the longer follow-up time. Of those who remained, 11% (4) were lost before the minimum study follow-up of 48 months or had incomplete datasets, leaving 89% (33) for analysis here at a median follow-up of 80 months (range 49 to 208 months). Periacetabular osteotomy or subtrochanteric rotational femoral osteotomy was added under the same anaesthesia time in 33% (11 patients). We added periacetabular osteotomy in 24% (8) when intraoperative anterior instability was present in external rotation. A femoral rotational osteotomy was added in 9% (3) when posterior instability was present in flexion and internal rotation. The mean ± standard deviation age at the time of surgery was 13 ± 1 years, and 33% (11 of 33) of patients were female. The mean slip angle was 51° ± 16º, and 15% (5) of hips had unstable slips, defined as an inability to walk with or without crutches. We documented chronic presentations in 82% (27) of patients, acute and chronic in 12% (4), and acute in 6% (2). The rate of symptomatic AVN was determined by reviewing all radiographs obtained at the latest follow-up interval. Further surgery and other complications were assessed through an electronic medical record review. Radiographic morphologic parameters were measured before surgery and at a minimum follow-up of 4 years by two senior orthopaedic surgeons. Radiographs obtained at the latest follow-up visit were also screened for signs of osteoarthritis by the same surgeons.

Results
At the latest follow-up, 3% (1 patient) of patients developed symptomatic AVN and underwent further surgery and 3% (1) underwent revision surgery for screw breakage after a high-energy fall. Postoperatively, the alpha angle was restored to 39º ± 6º, the anterior head-neck offset was restored to 8 ± 3 mm, the neck-shaft angle was 136º ± 6º, and the presence of a positive Klein line decreased from 64% (21 hips) to 0% (0 hips). No patients showed radiographic signs of osteoarthritis at the minimum follow-up of 4 years.

Conclusion
In this series, the modified Dunn procedure in moderate and severe slips was a reproducible procedure, and few patients developed symptomatic AVN or experienced other complications. Hip morphology was restored, but a longer follow-up duration and a detailed analysis of the results from other centers is warranted to assess the possible long-term risk of progression to AVN or osteoarthritis.

Level of Evidence
Level IV, therapeutic study.