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® 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.