Metallosis caused by alumina ceramic screw fixation of grafted bone in a bipolar hip endoprosthesis.

We report a case of metallosis due to ceramic fragments in the inner bearing surface of the polyethylene cup of a bipolar hip prosthesis with fracture of the alumina ceramic screws used for grafted bone fixation. After bone-grafting acetabuloplasty with a Bateman bipolar endoprosthesis, gradual migration of the outer head occurred, and fracture of the screws was observed. Seven years after the operation, radiographs showed severe metallosis of the surrounding tissues. At revision, marked wear of the inner head was seen. Detailed examination revealed that many rough-edged ceramic particles originating from the fractured ceramic screws had become embedded in the inner surface of the polyethylene bearing insert. These extremely hard ceramic fragments had entered the prosthetic joint space during joint movement, thereafter causing continuous abrasion of the metal head. After revision, the concentration of the constituents of the prosthesis alloy in the serum decreased toward control levels. To prevent serious complications like those in the present case, screws should be inserted more than 1 cm from the outer head of a bipolar endoprosthesis, and the outer head should be removed as soon as possible if it comes into contact with the screws.