Vitamin E-stabilized UHMWPE for total joint implants: a review

Abstract

Background: Osteolysis due to wear of UHMWPE limits the longevity of joint arthroplasty. Oxidative degradation of UHMWPE gamma-sterilized in air increases its wear while decreasing mechanical strength. Vitamin E stabilization of UHMWPE was proposed to improve oxidation resistance while maintaining wear resistance and fatigue strength.

Questions/purposes: We reviewed the preclinical research on the development and testing of vitamin E-stabilized UHMWPE with the following questions in mind: (1) What is the rationale behind protecting irradiated UHMWPE against oxidation by vitamin E? (2) What are the effects of vitamin E on the microstructure, tribologic, and mechanical properties of irradiated UHMWPE? (3) Is vitamin E expected to affect the periprosthetic tissue negatively?

Methods: We performed searches in PubMed, Scopus, and Science Citation Index to review the development of vitamin E-stabilized UHMWPEs and their feasibility as clinical implants.

Results: The rationale for using vitamin E in UHMWPE was twofold: improving oxidation resistance of irradiated UHMWPEs and fatigue strength of irradiated UHMWPEs with an alternative to postirradiation melting. Vitamin E-stabilized UHMWPE showed oxidation resistance superior to that of irradiated UHMWPEs with detectable residual free radicals. It showed equivalent wear and improved mechanical strength compared to irradiated and melted UHMWPE. The biocompatibility was confirmed by simulating elution, if any, of the antioxidant from implants.

Conclusions: Vitamin E-stabilized UHMWPE offers a joint arthroplasty technology with good mechanical, wear, and oxidation properties.

Clinical relevance: Vitamin E-stabilized, irradiated UHMWPEs were recently introduced clinically. The rationale behind using vitamin E and in vitro tests comparing its performance to older materials are of great interest for improving longevity of joint arthroplasties.

Fig. 1

A flowchart shows the processing steps for the incorporation of vitamin E into UHMWPE: blending versus diffusion.

Fig. 2A–B

A diagram illustrates the oxidation scheme of UHMWPE and the stabilizing mechanisms of vitamin E. (A) Due to radiolytic bond scission, free radicals are produced in irradiated UHMWPE, which react with oxygen and trigger the oxidation cascade (Reactions 1–4). Oxidation is accompanied by chain scissioning, deteriorating its mechanical properties. It is believed α-tocopherol can stabilize peroxy radicals formed by oxidation and can also directly react with alkyl macroradicals (Reactions 5 and 6). (B) The formed tocopheryl product can in turn interact with another alkyl macroradical, furthering the stabilizing effect.