Vitamin E diffused, highly crosslinked UHMWPE: a review

Abstract

Highly crosslinked UHMWPE has become the bearing surface of choice in total hip arthroplasty. First generation crosslinked UHMWPEs, clinically introduced in the 1990s, show significant improvements compared to gamma sterilised, conventional UHMWPE in decreasing wear and osteolysis. These crosslinked UHMWPEs were thermally treated (annealed or melted) after irradiation to improve their oxidation resistance. While annealing resulted in the retention of some oxidation potential, postirradiation melted UHMWPEs had reduced fatigue strength due to the crystallinity loss during melting. Thus, the stabilisation of radiation crosslinked UHMWPEs by the diffusion of the antioxidant vitamin E was developed to obtain oxidation resistance with improved fatigue strength by avoiding post-irradiation melting. A two-step process was developed to incorporate vitamin E into irradiated UHMWPE by diffusion to obtain a uniform concentration profile. Against accelerated and real-time aging in vitro, this material showed superior oxidation resistance to UHMWPEs with residual free radicals. The fatigue strength was improved compared to irradiated and melted UHMWPEs crosslinked using the same irradiation dose. Several adverse testing schemes simulating impingement showed satisfactory behaviour. Peri-prosthetic tissue reaction to vitamin E was evaluated in rabbits and any effects of vitamin E on device fixation were evaluated in a canine model, both of which showed no detrimental effects of the inclusion of vitamin E in crosslinked UHMWPE. Irradiated, vitamin E-diffused, and gamma sterilised UHMWPEs have been in clinical use in hips since 2007 and in knees since 2008. The clinical outcome of this material will be apparent from the results of prospective, randomised clinical studies. IntroductionOsteolysis triggered mainly by ultrahigh molecular weight polyethylene (UHMWPE) wear particles has been one of the major problems in total hip arthroplasty along with instability/dislocation and infection [7]. Highly crosslinked UHMWPEs were developed using high-dose irradiation (50-100 kGy) to decrease the wear rate of UHMWPE [44,46] and have become the standard-of-care after their first decade of service, especially in North America [61].Irradiation causes crosslinking in the amorphous phase of the UHMWPE [33], but also initiates the formation of free radicals in the crystalline phase [23], unable to recombine due to structural limitations, they become trapped for long periods of time [29]. These residual free radicals are believed to migrate to the crystalline/amorphous interface and cause oxidative degradation in the material [16][17][18]59, 69] through a cascade of reactions with oxygen [32,71].In first generation crosslinked UHMWPEs [34], postirradiation thermal treatment was used to increase the oxidation resistance (Fig. 1). One approach was to annealThe studies discussed here were performed by research funding in part from NIH/NIAMS

Wear Performance of UHMWPE and Reinforced UHMWPE Composites in Arthroplasty Applications: A Review

“…Furthermore, the amount of incorporated vitamin E is not affected by the crosslink density. Due to the saturation limit of the vitamin E blended UHMWPE at body temperature, the vitamin E concentration is approximately 0.7 wt% [46]. However, the UHMWPE has a risk of oxidation during irradiation and in storage until vitamin E is incorporated.…”

Total kalça artroplastisinde eklemleşme seçenekleri: Eklemleşme kime, hangi ikili?

“…Bu basamaklar, hammaddenin işlenmesi sırasında bir antioksidan olan vitamin E katkısı, radyasyon ile çapraz bağlanma sonrasında ısıl işlem ile eritme ve tavlama yapılması şeklinde olabilir. [5,11] UHMWPE'nin bu işlemlere maruz bırakılması sonucunda yıpranmaya karşı direnci belirgin şekilde artış göstermektedir. Mc Kellop ve ark.…”

“…In-vivo yapılan çift-kör prospektif randomize çalış-malar ve meta analizlerde de in-vitro ve ex-vivo ça-lışmalara benzer sonuçlar kaydedilmiştir. [7,11,12] Engh ve arkadaşlarının [13] 230 kalça üzerinde yürüttükleri ileriye dönük çalışmada, aynı üreticiye ait çapraz bağlı ve geleneksel ara parçalar aynı asetabuler ve femoral komponentler kullanılarak karşılaştırılmıştır. Dört yıllık takip sonuçlarına göre, yıllık doğrusal yıpranma oranları çapraz bağlı UHMPWE'lerde 0,01±0,07mm/ yıl iken geleneksel UHMWPE'lerde 0,20±0,13 mm/yıl olarak ölçülmüştür.…”

Periprosthetic osteolysis after total hip replacement: molecular pathology and clinical management

“…This has led to the development of a new generation of polyethylenes, namely highly cross-linked polyethylenes stabilised with vitamin E to reduce oxidation which appear to provide improved mechanical properties in vitro 74,75 . Long term results of these materials are not yet available.…”