Avascular Necrosis After Modified Dunn Surgery for the Treatment of Slipped Capital Femoral Epiphysis.

 The present study analyzed the incidence of epiphyseal avascular necrosis in patients with slipped capital femoral epiphysis (SCFE) treated using a modified Dunn technique. In addition, this study determined the correlation of other variables with this incidence and described treatment complications.  This is a retrospective study with 20 patients treated by the same surgical team from 2009 to 2019 and followed up for 2 to 12 years. The analysis included general features, time from presentation to surgical procedure, classification, and intraoperative blood perfusion of the epiphysis, as well as complications and their treatment.  All cases were severe; 65% were acute on chronic, and 55% of the SCFEs were unstable. Our complication rate was 45%, with 5 cases of avascular necrosis, 2 cases of deep infection, 1 case of material failure, and 1 case of joint instability. The statistical analysis revealed that the risk of necrosis was higher when the surgery occurred after a long hospitalization time and there was no intraoperative epiphyseal perfusion. Four necrosis cases happened within the first 5 years, and 1 case in the last 5 years of the study.  Our study showed that necrosis was the most common complication. It also revealed that surgery delay and lack of intraoperative epiphysis perfusion potentially predispose to avascular necrosis. Although with no statistical significance, coxofemoral instability occurred in chronic SCFE, and surgical fixation with threaded wires was less effective than fixation with a cannulated screw. The modified Dunn procedure should be reserved for severe cases in which other techniques are not feasible and performed by an experienced, trained, and qualified team.