Acetabular labrum entrapment following traumatic posterior dislocation of the hip.

In traumatic dislocation of the hip with or without a fracture of the acetabular rim, complete anatomical reduction might be prevented by a bone fragment or infrequently by a soft tissue block, such as a torn acetabular labrum, ruptured capsule, or round ligament. We report a rare case of a tear in the acetabular labrum that prevented complete reduction of the dislocated hip. A 26-year-old man suffered posterior dislocation of the right hip, which was reduced under general anesthesia. The postreduction radiograph showed that the reduction was not complete, and a thin bony fragment was observed in the joint space in the weight-bearing area. Open reduction was performed 11 days later. We found a free bone fragment in the joint space, which was removed. The postoperative radiograph still did not show complete reduction of the hip. A large defect in the contrast medium was shown in the widened joint space by arthrography, which revealed the existence of the soft tissue interposition. We then performed a second operation and learned that the acetabular labrum was widely detached from the anterior to the posterior acetabular rim and was lying deep within the acetabulum. This detached portion of the labrum was excised, and the hip was reduced. The radiograph obtained during surgery then showed complete, concentric reduction. We missed the diagnosis clinically and radiologically at the first operation, proving how important it is to obtain an accurate radiological diagnosis in the operating room.