Comparative micro-Raman study on standard, cross-linked and vitamin E-blended polyethylene acetabular cups after long-term in vitro testing and ageing

Ultra-high molecular-weight polyethylene has been used in total joint replacement for the last three decades. Many attempts have been made to improve the wear behaviour of this material. Highly cross-linked polyethylene (XLPE) has been developed to decrease the wear rate, while the addition of stabilizers such as vitamin E has been proposed to slow the oxidation processes. In this study, we compared the wear behaviour of conventional ultra-high molecular-weight polyethylene, XLPE and vitamin E-added XLPE acetabular cups for total hip arthroplasty. The samples were run for five million cycles on a hip joint simulator (first test), then underwent an accelerated ageing treatment, were tested again for two million cycles (second test) and finally were run for another two million cycles in presence of third-body particles (third test). Our study showed that vitamin E-added XLPE cups had a better wear behaviour only in the long-term and more severe testing conditions: in the third test, they underwent the lowest increase in wear rate. Micro-Raman spectroscopy allowed us to analyse the wear degradation of the cups on a molecular scale, and differences in the wear mechanisms were revealed. The presence of vitamin E did not prevent structural changes upon the first test, while it did in ageing and in the second test. In the third test, more significant structural changes were observed; the XLPE cups, which lost the lowest mass, had the most modified articular surface. These morphological aspects should be taken into account, together with gravimetric wear rates, in the characterization of wear degradation. Copyright © 2017 John Wiley & Sons, Ltd.