Low Rate of AVN and Complications in Unstable SCFE With Epiphyseal-metaphyseal Discontinuity After Treatment With a Modified Dunn Procedure
Authors: Ziebarth Kai , Lerch Till D. , Kaim Tilman , Schwab Joseph M. , Steppacher Simon D. , Tannast Moritz , Siebenrock Klaus A. 
Published: June 2024

Background
The risk of developing avascular necrosis (AVN) in the setting of an unstable slipped capital femoral epiphysis (SCFE) that is undergoing treatment with the modified Dunn procedure is not well understood. In addition, since the Loder classification of unstable is reportedly different than actual intraoperatively observed instability (that is, discontinuity between the femoral head epiphysis and proximal femoral metaphysis), the overall risk of developing AVN, as well as the potential complications of treatment of these patients with the modified Dunn procedure, are unknown.

Questions/purposes
To evaluate the modified Dunn procedure for the treatment of patients with epiphyseal-metaphyseal discontinuity, we asked: (1) What was the survivorship free from AVN at 10 years? (2) What was the survivorship free from subsequent surgery and/or complications at 10 years? (3) What were the clinical and patient-reported outcome scores?

Methods
In a retrospective analysis, we identified 159 patients (159 hips) treated with a modified Dunn procedure for SCFE between 1998 and 2020, of whom 97% (155 of 159) had documentation about intraoperatively observed epiphyseal-metaphyseal stability. Of those, 37% (58 of 155) of patients were documented to have intraoperatively observed epiphyseal-metaphyseal discontinuity and were considered eligible for inclusion, whereas 63% (97 of 155) had documented epiphyseal-metaphyseal stability and were excluded. No patients were lost to follow-up before the 2-year minimum. All patients were assessed for survival, but 7% (4 of 58) did not fill out our outcomes score questionnaire. This resulted in 93% (54 of 58) of patients who were available for outcome score assessment. Additionally, 50% (29 of 58) of patients had not been seen within the last 5 years; they are included, but we note that there is uncertainty about their status. The median (range) age at surgery was 13 years (10 to 16), and the sex ratio was 60% (35 of 58) male and 40% (23 of 58) female patients. Sixty-four percent (37 of 58) of patients were classified as acute-on-chronic, and 17% (10 of 58) of patients were classified as acute. Forty-seven percent (27 of 58) of patients presented with severe slips and 43% (25 of 58) of patients with moderate slips based on radiographic classification. All patients underwent surgical hip dislocation with the modified Dunn procedure to correct the slip deformity and provide stabilization. Complications and reoperations were assessed from a review of electronic medical records, and a Kaplan-Meier estimator was used to estimate survivorship free from complications and reoperations at 10 years. Clinical examination results and questionnaire responses were evaluated at minimum 2-year follow-up.

Results
Kaplan-Meier survivorship free from AVN was 93% (95% CI 87% to 100%) at 10 years. Survivorship free from any reoperation was 75% (95% CI 64% to 88%) at 10 years. In addition, survivorship free from complications, defined as development of AVN, reoperation, or a Sink Grade II complication or higher, was 57% (95% CI 45% to 73%) at 10 years. The median (range) Merle D’Aubigne Postel score was 18 (14 to 18) for the patients who did not develop AVN, and 12 (6 to 16) for the four patients who developed AVN (p < 0.001). The median modified Harris hip score was 100 (74 to 100) in the non-AVN cohort and 65 (37 to 82) in the AVN cohort (p = 0.001). Median HOOS total score was 95 (50 to 100) in the non-AVN cohort and 53 (40 to 82) in the AVN cohort (p = 0.002).

Conclusion
Although the modified Dunn procedure is technically challenging, this study shows that in experienced hands, patients with who have demonstrated epiphyseal-metaphyseal discontinuity can be treated with a low risk of AVN and subsequent surgery. Referral of these patients to specialists who have substantial expertise in this procedure is recommended to improve patient outcomes. Prospective, long-term observational studies will help us identify these high-risk patients preoperatively and determine the long-term success of this procedure.

Level of Evidence
Level IV, therapeutic study.