EFFECT OF HEAD SIZE AND CROSSLINKING ON WEAR IN POLYETHYLENE ACEATABULAR COMPONENTS

Abstract

Polyethylene (PE) wear affects survivorship in the long term while dislocation remains a significant factor in the short term. Increasing head size can reduce impingement and dislocation. However, this increases wear rates and reduces the net thickness of the liner. Several reports have demonstrated significant reduction in wear in cross-linked PE. This study reports wear rates in crosslinked PE liners with increased head size. Four groups of PE liners were tested against cobalt-chrome heads in a hip wear simulator: highly crosslinked liners with head size 28mm (28XPE) and 32mm (32XPE), and minimally crosslinked liners with head size 28mm (28PE) and 32mm (32PE). Additional liners were used as load-soak controls to monitor weight gain due to fluid absorption. Gravimetric analysis was performed every 500,000 cycles for a total of 5,000,000 cycles. 28PE and 32PE liners had mean wear rates of 12.5(±1.0) and 17.45 (±2.6) mg/million cycles. Both highly crosslinked PE liners (28XPE and 32XPE) had significant less wear rates that regular polyethylene 1.49 (±0.72) and 2.55 (±0.19) mg/million cycles respectively. Increasing head size resulted in increased wear, which is consistent with previous reports. Highly crosslinked PE significantly reduced wear rates in both head sizes. Although there was a small increase in wear in the 32XPE group compared to the 28XPE group, wear was significantly less than both 32PE and 28PE groups. These encouraging results suggest that a dual benefit (reduced wear and reduced dislocation rate) might be achieved using 32XPE liners. Further studies that evaluate fatigue damage, crack propagation and impingement are necessary.