Fig. 4From: The Kocher-Langenbeck approach combined with robot-aided percutaneous anterior column screw fixation for transverse-oriented acetabular fractures: a retrospective studyThe complication of heterotopic ossification in one case. a An isolated fragment is located at the lateral side of the femoral head (red arrow). b A postoperative radiograph shows that the fragment was not removed (red arrow). c An antero-posterior view shows heterotopic ossification with grade II at the affected hip joint at one-year follow-upBack to article page