An Unusual Mechanical Cause of Hip Subluxation Following Modified Dunn Procedure for Slipped Capital Femoral Epiphysis: A Case Report

Abstract Postoperative hip instability occurs in approximately 4% of patients after modified Dunn procedures for slipped capital femoral epiphysis (SCFE), typically attributed to capsular laxity. A 13-year-old boy with severe SCFE (Southwick angle 55°) underwent a modified Dunn procedure. Immediate postoperative radiographs revealed hip subluxation. Computed tomography imaging confirmed subluxation with an intra-articular shadow. Emergency revision surgery identified a 2 cm × 3 cm cartilage fragment lodged between the femoral head and acetabulum. Fragment removal resulted in complete joint restoration and successful recovery. This case demonstrates an unusual mechanical cause of postoperative hip subluxation. Unlike typical cases caused by capsular laxity, this subluxation resulted from intra-articular debris creating mechanical blockage. Early identification prevented potentially devastating complications. Intra-articular fragments can cause residual hip subluxation after modified Dunn procedures. Surgeons should consider joint inspection under direct vision or fluoroscopy before capsular closure when hip instability is suspected.