Low wear, high stability - promises of success in a moderately cross-linked cup?

Purpose: Cross-linking has proven effective in reducing polyethylene wear in total hip replacements. However, increasing the amount of cross-links will impair other mechanical properties of the polyethylene. The optimal threshold of crosslinking has still not been established. This led to the development of a moderately cross-linked (5 Mrad) cemented cup in which wear and stability is yet to be determined. Methods: A total of, 70 hips were included in this case series on the cemented Marathon (R) cup. Mean age of the patients was 78 years (SD 15). We measured wear and migration by radiostereometry at 3, 12 and 24 months. Results: The proximal wear rate estimate between 3 to 24 months was 0.036 mm/year, and a total proximal wear estimate at 2 years of 0.11 mm (95% CI 0.09-0.14). Translations and rotations along the 3 cardinal axes were all at or below the precision limit, and less than what is believed to be predictive of later loosening, namely 0.2-1 mm for proximal migration. The cups remained stable after the initial "bedding in" that occurred during the first 3 months. Conclusions: Our results indicate that moderate cross-linking (5Mrad) yields low wear and high stability in this specific acetabular cup, comparable to other cups with higher cross-linking.