Abstract
BACKGROUND: The Universal 2 total wrist arthroplasty was one of the most common wrist replacements, but long-term results were disappointing, due to substantial damage to the polyethylene component and, in some cases, metallosis. The purpose of this research was to investigate the underlying reasons for this polyethylene damage. MATERIALS AND METHODS: From a single clinical center, retrieval analysis was undertaken on six Universal 2 wrists and two additional polyethylene components. All components were analyzed at the macroscale and dimensional measurements of polyethylene components were undertaken. These were compared against known component orientation in vivo to identify areas of greatest material loss. RESULTS: Of 62 Universal 2 wrists implanted, there was a tendency for smaller implants to be revised more frequently. Of the six explanted wrists, material loss was always noticeable on the ulnar side, and to a lesser extent in the dorsal direction. Five of eight polyethylene components had failed at the base of the ulnar-side blind hole. Smaller implants tended to have less thickness at the base of the blind holes, thus explaining the failure of smaller sizes. Discoloration and surface fatigue of explants indicated oxidation of components. Average time in vivo for the explants was 13.8 years which indicates the slow nature of polyethylene oxidation. All were revised due to loosening. All were implanted in rheumatoid patients with a mean age at surgery of 56.1 years. Three of the six Universal 2 wrists, all sized Extra Small, showed severe wear of the titanium alloy carpal component. CONCLUSION: Failure of the polyethylene components was due to a combination of inappropriate sterilization technique plus a design issue where polyethylene was thinnest on the smallest size components. Continued surveillance of patients implanted with Universal 2 wrists is recommended.