Low wear with vitamin E-infused highly cross-linked polyethylene : 14 years' follow-up of a randomized radiostereometric analysis study

Abstract

Aims: Highly cross-linked polyethylene (HXLPE) infused with vitamin E was introduced at the beginning of the 21st century. Vitamin E removes free radicals arising during gamma irradiation in order to cross-link the polyethylene. Removing free radicals was hypothesized to preserve mechanical properties and wear behaviour of the polyethylene in vivo. Excellent polyethylene wear behaviour of other HXLPEs has encouraged surgeons to use larger heads in total hip arthroplasty (THA) to address prosthesis dislocation. It is still unclear whether polyethylene wear remains low in the long term when using larger femoral heads. The aim of this study was to evaluate long-term polyethylene wear in uncemented THA with vitamin E-infused HXLPE liners with 32 or 36 mm ceramic femoral heads.

Methods: A total of 50 hips allocated to uncemented THA were included in this prospective randomized controlled trial from January 2009 to February 2010. They were randomized to either 32 or 36 mm Biolox Delta ceramic heads. The primary outcome was polyethylene wear measured with markerless radiostereometric analysis. The secondary outcome was patient-reported outcome measures measured by Harris Hip Score, Oxford Hip Score, and University of California, Los Angeles activity scale.

Results: At final follow-up (14 years), 32 hips were available for analysis (32 mm, n = 17; 36 mm, n = 15), and 18 hips had been lost to follow-up or were excluded: two hips due to infection, and one hip due to periprosthetic fracture. These three revised hips were excluded due to removal and/or change of prosthesis components. Mean polyethylene wear in the proximal direction was 0.10 mm (95% CI 0.05 to 0.16) and 0.01 mm (95% CI -0.06 to 0.07) for 32 and 36 mm femoral heads, respectively (p = 0.022). After the 'bedding-in' period wear was 0.04 mm (95% CI -0.02 to 0.11) and 0.02 mm (95% CI -0.06 to 0.10) for 32 and 36 mm, respectively (p = 0.628).

Conclusion: Polyethylene wear was extremely low for vitamin E-infused HXLPE with 36 mm ceramic femoral heads at 14 years of follow-up. There was no difference in wear between 32 and 36 mm heads after the 'bedding-in' period. The clinical outcome was excellent. Biolox Delta ceramic heads on vitamin E-infused HXLPE seem to be a safe option for 36 mm heads.