This article describes a case of late locking mechanism failure and disassociation of a Pinnacle acetabular cup (DePuy, Warsaw, Indiana) and Marathon polyethylene liner (DePuy) 53 months after routine primary total hip arthroplasty in an active patient. Following an uncomplicated initial postoperative recovery, the patient felt a pop while kneeling for gardening activities. The patient had no prodromal symptoms but reported pain with range of motion and weight bearing following the episode. Radiographs appeared to show a fractured liner with intact acetabular and femoral components. Intraoperatively, the liner was disassociated and dislocated inferior to the acetabulum, and 3 consecutive antirotational tines were sheared off the liner at their bases. The acetabular cup and femoral stem were well fixed. Extensive metallosis existed from the femoral head and acetabular shell articulating in the absence of a liner. The patient underwent revision of the acetabular cup, polyethylene liner, and femoral head due to the concern for osteolysis given the extensive metallosis. Revision of the acetabular cup and liner were performed with no further complications. No conclusions could be made as to the exact mechanism of failure following laboratory analysis of the retrieved polyethylene liner. Several possible mechanisms of failure are possible. Although cases of acute disassociation of this system have been reported, this is the first article to our knowledge to report failure at such a late postoperative time.
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