Obturator Internus Muscle Entrapment in Posterior Wall Acetabular Fractures: A Rare Intraoperative Finding

Abstract Introduction: We report two cases of the rare presentation of obturator internus muscle entrapment in posterior wall fractures of the acetabulum. While piriformis muscle entrapment has been previously reported, there are no known cases of obturator internus entrapment associated with posterior wall fractures of the acetabulum. Case Presentation: Case 1: A 38-year-old male presented with right hip and knee pain following a road traffic accident. He was diagnosed with a posterior wall and posterior column fracture, accompanied by posterior dislocation of the knee. During surgery, the obturator internus muscle was found interposed between the fracture site and the displaced posterior wall fragment. Case 2: A 43-year-old male sustained blunt abdominal trauma and a Pipkin type 4 (femoral head fracture with posterior wall fracture) injury following a road traffic accident. After stabilization of his abdominal injury with laparoscopic mesenteric repair, the patient underwent open reduction and internal fixation of the posterior wall fracture, along with removal of intra-articular bony fragments from an infra-foveal femoral head fracture. Similarly, during the procedure, the obturator internus muscle was found interposed between the fracture site and the displaced posterior wall fragment. Both patients followed a standard post-operative rehabilitation protocol and recovery was uneventful. Conclusion: These cases highlight the importance of recognizing muscle entrapment as a potential cause of difficulty in reducing posterior acetabular wall fractures. Proper identification and management of such interpositions are crucial to ensure successful fracture reduction and fixation.