FIRST GENERATION ONCE ANNEALED HIGHLY CROSS-LINKED POLYETHYLENE EXHIBITS LOW WEAR AT 12 YEARS

Background A first generation once annealed highly crosslinked polyethylene (HXLPE) was introduced in 1998. At 8 years it was reported to have a 78% reduction in wear compared with conventional polyethylene and no osteolysis. However, concerns regarding the long-term performance and oxidative resistance of this annealed material exist because of the presence of free radicals. Questions/purposes We therefore addressed the following questions: (1) Does the improvement in wear observed at earlier follow-up continue out to 15 years? (2) What is the incidence of osteolysis in this group of patients? Methods We retrospectively reviewed 48 prospectively followed patients who had 50 hips with a once annealed HXLPE and were followed an average of 12 years (15 years maximum). Linear head penetration and cup position were measured from AP radiographs at early, 1-year, 5-year, and most recent follow-ups. There were 26 females, 22 males, with an average age of 61 years. Results At average 12 years follow-up, annual linear wear was 0.018 mm (SD = 0.024). Average cup inclination was 50.2 degrees (SD = 5.1 range 48 to 64) and anteversion was 18.6 (SD = 8.3, range 3 to 35). No mechanical failure or osteolysis has been found on routine x-rays to date. Conclusions At 8 year follow this once annealed material had a reported linear wear rate of 0.031mm /year. We now report, at a 12 years average 15 years maximum follow-up, a further reduction in linear wear of 0.018mm/yr. and no mechanical failures or osteolysis (Figure-1).