Effect of an Extended Period of Accelerated Aging on VEXLPE Wear

Vitamin E stabilized, highly cross-linked polyethylene (VEXLPE) is used as a bearing material in joint replacements in growing numbers. Regarding its wear performance, short and mid-term clinical follow-up studies are highly promising. To simulate possible long-term in vivo oxidative degradation, 200 VEXLPE specimens were subjected to an extended period of accelerated aging, 6 weeks, in ASTM F2003 conditions (pure O2, 70 ˚C, 0.5 MPa). They were then concurrently wear tested with the validated, multidirectional SuperCTPOD-200 device for 3 million cycles (94.2 km, 833 h) in diluted serum. Their wear factor proved to be 1.71 ± 0.22 × 10−7 mm3/Nm (n = 200). The mean was 4.4% higher than that before the aging, and the difference was statistically significant (p = 0.001). This was the first time that a comparison of unaged and aged VEXLPE wear was made using large sample sizes. Nevertheless, the present wear factors were below the clinical osteolysis threshold and therefore not a cause for concern. In other words, the 4.4% increase in the wear rate would be clinically insignificant. Vitamin E stabilization of the present VEXLPE proved highly durable.