Temporary in Situ Pinning With Subsequent Modified Dunn is a Safe Alternative to Primary Modified Dunn in Moderate and Severe Slipped Capital Femoral Epiphysis

BACKGROUND: Surgical hip dislocation with modified Dunn procedure (MD) is a viable treatment option for moderate to severe slipped capital femoral epiphysis (SCFE). In the acute setting, an experienced surgeon may not be immediately available for the MD. However, in situ pinning (ISP) is a well-accepted initial treatment and may be more familiar to the on-call orthopaedic surgeon. Our aim was to compare outcomes at short and midterm follow-up in patients with moderate/severe SCFE undergoing ISP with subsequent MD versus primary MD. METHODS: Between June 2017 and July 2024, we treated 29 patients for SCFE. During this time, we generally indicated the modified Dunn procedure when the slip angle was ≥30 degrees. Radiographic morphologic parameters were measured before surgery and at a minimum follow-up of 8.5 months. Radiographs at final follow-up were also screened for signs of osteoarthritis by the senior hip surgeon. After adjusting for age and sex, we used multivariable linear regression to assess differences in continuous outcomes between the ISP+MD and MD-only groups, and logistic regression to evaluate differences in the odds of binary outcomes between groups. The Wilcoxon rank-sum test tested differences in the distribution of Merle d'Aubigné scores between groups. RESULTS: Twelve patients underwent initial ISP with subsequent MD; 17 patients underwent primary MD. Median time between ISP and MD was 35 days (range: 5 to 137 d). There was no difference in complication rate between groups, including the incidence of AVN (17% in ISP+MD vs. 12% in MD; P≥0.99). Merle d'Aubigné scores at final follow-up were 18 (interquartile range: 16 to 18) in the ISP+MD group versus 17 (interquartile range: 16 to 18) in the MD group (P=0.36). There were no significant differences in radiographic outcomes between groups at final follow-up. CONCLUSION: In this series, a temporary ISP before modified Dunn in moderate and severe slips was a safe alternative to primary MD if an experienced hip surgeon was not immediately available. This allows for optimization regarding surgical timing with an experienced hip surgeon, preoperative patient and family education of surgical risks and benefits, and postoperative compliance with precautions after MD. A longer follow-up duration and results from other centers are warranted for this approach. This study contains a small patient cohort and may be underpowered to detect smaller differences that may be detectable with a higher-powered study. LEVEL OF EVIDENCE: Level II, prospective comparative study.