In vivo wear of bipolar endoprosthesis

In vivo wear was evaluated in 39 bipolar endoprostheses retrieved at revision surgery. The duration from the implantation until the revision surgery was 5.2 +/- 1.3 years. The annual wear rate of the inner articulation was 0.21 mm, and the annual wear rate (in depth) of the polyethylene rim was 0.54 mm. The annual wear rate of the rim was greater in cases with radiological osteolysis than in those without osteolysis. Improvement in the configuration of the rim, and the device such as coating the stem neck with a cobalt-chromium alloy mirror surface are necessary to prevent rim abrasion. It is also important to make careful consideration on the indication of bipolar endoprosthesis especially for cases of dysplastic osteoarthritis, in which rim abrasion was found to be very severe.