PURPOSE OF STUDY: Total joint replacements (TJR) have become the cornerstone of modern orthopedic surgery. A great majority of TJR employs ultrahigh molecular weight polyethylene (UHMWPE) liners. TJR manufacturers use many different types of UHMWPE, which are modified by various combinations of crosslinking, thermal treatment, sterilization and/or addition of biocompatible stabilizers. The UHMWPE modifications are expected to improve the polymer's resistance to oxidative degradation and wear (release of microparticles from the polymer surface). This manuscript provides an objective, non-commercial comparison of current UHMWPE formulations currently employed in total knee replacements. MATERIALS AND METHODS: UHMWPE liners from 21 total knee replacements (TKR) were collected which represent the most implanted liners in the Czech Republic in the period 2020-2021. The UHMWPEs were characterized using several methods: infrared microspectroscopy (IR), non-instrumented and instrumented microindentation hardness testing (MH and MHI), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and solubility measurements. The above-listed methods yielded quite complete information about the structure and properties of each UHMWPE type, including its potential long-term oxidation resistance. RESULTS: For each UHMWPE liner, IR yielded information about immediate oxidative degradation (in the form of oxidation index, OI), level of crosslinking (trans-vinylene index, VI) and crystallinity (CI). The MH and MHI testing gave information about the impact of structure changes on mechanical properties. The remaining methods (DSC, TGA, and solubility measurements) provided additional information regarding the structure changes and resistance to long-term oxidative degradation. Statistical evaluation showed significant differences among the samples as well as interesting correlations among the UHMWPE modifications, structural changes, and mechanical performance. DISCUSSION: Surprisingly enough, UHMWPE materials from different manufacturers showed quite different properties, including the resistance against the long-term oxidative degradation, which is regarded as one of the main reasons of TJR failures. The most promising UHMWPE types were crosslinked materials with biocompatible stabilizers. CONCLUSIONS: Current UHMWPE liners from different manufactures used in total knee replacements exhibit significantly different structure and properties. From the point of view of clinical practice, the traditional UHMWPE types, which contained residual radicals from irradiation and/or gamma sterilization, showed inferior resistance to oxidative degradation and should be avoided. The best properties were observed in modern UHMWPE types, which combined crosslinking, biocompatible stabilizers, and sterilization by ethylenoxide or gas plasma. KEY WORDS: UHMWPE; knee replacements; oxidative degradation; infrared spectroscopy; microhardness.
- MeSH
- biokompatibilní materiály chemie MeSH
- diferenciální skenovací kalorimetrie MeSH
- lidé MeSH
- polyethyleny * chemie MeSH
- protézy - design MeSH
- protézy kolene * MeSH
- termogravimetrie MeSH
- testování materiálů * metody MeSH
- totální endoprotéza kolene * přístrojové vybavení metody MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
- srovnávací studie MeSH
Ultra-high molecular weight polyethylene (UHMWPE) is the most important but, at the same time, the most vulnerable component of the total joint replacements. It is mainly used in hip and knee replacements. UHMWPE liners are the most loaded components of the implants. Consequently, the main material-related reasons of artificial joint failures are wear and oxidative degradation of the polymer. Resistance to wear is increased by radiation-induced crosslinking. Oxidation stability is enhanced by means of suitable thermal treatment. The most recent trend is to employ a biocompatible stabilizer based on the α-tocopherol in combination with suitable types of steric hindered amines for further improvement and fine-tuning of UHMWPE performance. This review summarizes the recent developments in UHMWPE modifications which should further increase lifespan of total joint replacements.
- MeSH
- alfa-tokoferol chemie MeSH
- antioxidancia chemie klasifikace MeSH
- chemické jevy MeSH
- ionizující záření MeSH
- lidé MeSH
- oxidace-redukce MeSH
- polyethylen * chemie MeSH
- protézy kloubů * MeSH
- selhání protézy MeSH
- synoviální tekutina MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
Ultra-high molecular weight polyethylene (UHMWPE) is used as a bearing material in total joint replacements. These joint replacements are in contact with the body fluids during their lifetime, resulting in material degradation. Due to the limited flow behaviour and the large number of physical entanglements of UHMWPE, some measurements (rheological measurements, determination of the gel content and extractable fraction, etc.) cannot be properly evaluated. Therefore, we have focused on accelerated aging of high density polyethylene (HDPE) in the hydrogen peroxide oxidation environment, allowing complete evaluation of degradation damage by monitoring mechanical, rheological, thermal and spectroscopic changes of the material. Perspective amine antioxidants (HALS) and the classical phenolic stabilizer α-tocopherol were used for HDPE stabilization and their effects compared. The aim of the work was to find an effective and rapid method of evaluating the antioxidant effect of newly developed stabilizers for UHMWPE using accelerated aging tests of lower molecular weight analogues. The results have shown that radiation crosslinking of HDPE leads to materials with higher sensitivity to oxidation. All tested stabilizers effectively inhibited the oxidation of HDPE. Moreover, after irradiation and subsequent aging, the branching of HALS stabilizer-containing HDPE chains took place which resulted in increased material resistance.
