O1134 IN VIVO WEAR AND PERFORMANCE OF HIGH CROSS LINKED POLYETHYLENE CUPS. A RSA STUDY OF 30 HIPS

Abstract

Aim: Investigate wear and performance of high cross linked plastic cups in vivo. Methods: Thirty cemented total hip arthroplasties done in patients with a mean age of 67 years (49–81) and weight of 74 kg (45–98). In twenty hips a standard gamma in air sterilized polyethylene plastic cup was used and in 10 hips a high cross linked plastic, (7.5 Mrad cold irradiated, sub melt annealed and gamma sterilized in inert (Crossfire®)). Exeter stems with 28 mm metal heads and Palacos-G cement were used in all. RSA measurement of wear and cup migration was done over 2 years and standard radiographs and Harris hip score also followed. Results: The cups had a similar head penetration the first 2 months, 46 and 61 um, and mainly due to plastic creep. Between 2 and 24 months the mean proximal wear (head penetration) was 156 um for Exeter and 13 um for Crossfire. (p< 0.001. T-test).

The mean vectorial migration was 0.31 and 0.24 mm and change in inclination 0.2° and 0.2° for the groups. (p> 0.8) Harris Hip Score was 92/96 and the radiological and clinical performance was equal after 2 years. Conclusion: High cross linked polyethylene showed a wear reduction of 90% compared to standard polyethylene after 2 years. The reduced wear was not at the expense of increased migration or radiolucences. High cross linked plastic looks promising but to what extent the decrease in wear reflects a decrease in clinical loosening and osteolyses remains to be shown.