Background: Free radicals formed in the cross-linking process may over time alter the mechanical properties of highly cross-linked polyethylene. Vitamin E-infused highly cross-linked polyethylene was therefore developed to achieve low wear-rate and good mechanical properties in the long term.
Aim: To present 6-year results from the initial randomised controlled trial.
Patients and methods: We measured wear and periacetabular bone remodelling in cementless total hip arthroplasty; 32- or 36-mm Biolox Delta heads and vitamin E-infused highly cross-linked polyethylene (E-Poly) were used. Markerless radiosterometric analysis measured the in vivo wear and dual energy x-ray absorptiometry was used to analyse bone remodelling in 40 hips at 6-year follow-up.
Results: In the proximal direction the wear for 32- and 36-mm heads was 0.15 mm (95% confidence interval [CI], 0.08-0.21) and 0.06 mm (95% CI, -0.002-0.12), respectively (p = 0. 015). However, between 3 months and 6 years (excluding the period of "bedding in"), the proximal wear for 32- and 36-mm heads was 0.10 mm (95% CI, 0.05-0.15) and 0.05 mm (95% CI, -0.01-0.11), respectively (p = 0.12). The annual proximal wear rate for 32- and 36-mm heads from 3 months to 6 years was 0.02 mm and 0.01 mm, respectively. There was no difference in bone remodelling around the cup from baseline to 6 years for the total material and no differences between study groups.
Conclusion: Wear of this vitamin E-infused highly cross-linked polyethylene is still low at 6-year follow-up, with no significant difference in wear from 3 months to 6 years between 32- and 36-mm heads.
Keywords: Cross-linked; RSA; THA; hip; radiosterometric; vitamin E.