Oxidation in orthopaedic UHMWPE sterilized by gamma-radiation and ethylene oxide

Background Highly crosslinked and thermally treated polyethylenes were clinically introduced to reduce wear and osteolysis. Although the crosslinking process improves the wear performance, it also introduces free radicals into the polymer that can subsequently oxidize. Thermal treatments have been implemented to reduce oxidation; however, the efficacy of these methods with regard to reducing in vivo oxidative degradation remains to be seen. Polyethylene oxidation is a concern because it can compromise the ultimate strength and ductility of the material. Questions/purposes We analyzed the oxidation, oxidation potential, and mechanical behavior of thermally treated highly crosslinked polyethylene retrieved acetabular liners. Methods Three hundred seven acetabular liners were collected from consecutive revision surgeries at six institutions over a 10-year period. Twenty-four were sterilized using nonionizing methods, 43 were sterilized in an inert environment, 80 were highly crosslinked and annealed, and 160 were highly crosslinked and remelted. Oxidation and oxidation potential were assessed by Fourier transmission infrared spectroscopy. Mechanical behavior was assessed by the small punch test. Results Oxidation and hydroperoxide (oxidation potential) indices were elevated in the annealed and gamma inert sterilized groups compared with those of the remelted liners and uncrosslinked gas sterilized controls, particularly at the rim. We also detected an increase in oxidation over time at the bearing surface of the remelted group. Ultimate strength of the polyethylene at the bearing surface was negatively correlated with implantation time for the annealed liners. Conclusions Within the first decade of implantation, the clinical outlook for first-generation highly crosslinked polyethylene remains promising. However, ongoing research continues to be warranted for first-generation highly crosslinked polyethylene bearings to monitor the implications of elevated oxidation at the rim of annealed liners as well as to better understand the subtle changes in oxidation at the bearing surface of remelted liners that occur in vivo.

Section: Methodsmentioning

confidence: 99%

Do First-generation Highly Crosslinked Polyethylenes Oxidize In Vivo?

MacDonald

Sakona

Ianuzzi

et al. 2011

“…Oxidation and subsequent embrittlement of UHMWPE decrease the abrasive wear resistance and increase the wear debris associated with the polymer [9,27,28,49]. Radiation crosslinking of UHMWPE reduces wear in vitro [48,50,51,53] and in vivo [29,47] but also induces free radicals, which can cause oxidation.…”

Section: Introductionmentioning

confidence: 99%

“…The major physiologic role of vitamin E [64] is to react with free radicals in cell membranes and protect polyunsaturated fatty acids from degradation due to oxidation [14,41,76,78,80]. Oxidation reactions in polyethylene, which contains very long, mostly saturated aliphatic chains, are believed to follow a mechanism similar to that in lipids [1,27].…”

Section: Introductionmentioning

confidence: 99%

Vitamin E-stabilized UHMWPE for Total Joint Implants: A Review

Bracco

Oral

2011

256

162

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.

“…The cross-linking and degradation reactions of UHMWPE are governed by free-radical reaction pathways [3]. For the reactions to proceed, free radicals must be formed in the PE by high-energy irradiation.…”

Section: Discussionmentioning

confidence: 99%

“…The reported wear values for gamma-irradiated UHMWPE depend on the aging conditions such as accelerated aging condition (eg, stored in a heat chamber), shelf life for stored implants, and in vivo aging [2,3,11,26].…”

Section: Introductionmentioning

confidence: 99%

Oxidation and Wear of 100-Mrad Cross-linked Polyethylene Shelf-aged for 30 Years

Kim

Oonishi

Kyomoto

et al. 2008

Some previous studies suggest that aging influences wear and oxidatively degraded nonsterilized ultra-high-molecular-weight polyethylene (UHMWPE) exhibits decreased wear resistance. We therefore asked whether shelf-aging storage conditions influenced degradation and wear resistance of gamma-irradiated UHMWPE. We examined oxidation and wear of 100-Mrad gamma-irradiated UHMWPE (100-Mrad polyethylene) cups shelf-aged for 30 years without (n = 2) or with (n = 2) packages. The oxidation index of the unpackaged 100-Mrad polyethylene surface (4) was higher than that of the packaged one (2.7). The packaged 100-Mrad polyethylene cup exhibited a high wear resistance with a steady wear rate of 0.5 mg/10 6 cycles. In contrast, the unpackaged 100-Mrad polyethylene exhibited an extremely high initial wear rate of 187.9 mg/10 6 cycles over the first 0.25 · 10 6 cycles with a subsequently reduced wear rate of 5 mg/10 6 cycles after 5 · 10 6 cycles. Packaging over long periods inhibits surface oxidation and maintains the wear resistance of gamma-irradiated UHMWPE cups.