Vitamin E Highly
Crosslinked UHMWPE
Materials for bearing surfaces in Total Knee Arthroplasty (TKA) need to comply with 3 important requirements: mechanical strength, wear resistance, and chemical stability. Ultrahigh molecular weight polyethylene (UHMWPE) is the preferred material due to its toughness, fatigue strength, and abrasion resistance.[1]
Highly crosslinked UHMWPE is an alternative to increase wear resistance, but the high dose of radiation applied to obtain crosslinking causes the formation of free radicals, which might encourage oxidative degradation of the material through the interaction with oxygen.[1, 2, 3]
Post-irradiation thermal treatments are applied to reduce the presence of free radicals. However, such treatments could diminish the mechanical properties of the material.[2]
Vitamin E Highly Crosslinked UHMWPE
E-CROSS is highly crosslinked UHMWPE blended with Vitamin E, a powerful antioxidant that stabilizes free radicals and improves oxidation resistance.[4,5] E-CROSS specific blend allows for an excellent performance in terms of wear and oxidation resistance without compromising the mechanical properties.[3]
Vitamin E is widely present in the human body and it is the most effective antioxidant: it reacts with free radicals in cell membranes and protects macro-constituents from degradation due to oxidation.[2]
Vitamin E reacts with free radicals of highly crosslinked UHMWPE and prevents their reaction with oxygen, resulting in E-CROSS oxidation resistance.[2, 7, 10]
By stabilizing free radicals, the material is more resistant to ageing and ageing-related complications, such as delamination and wear.[6,10]
In the context of improving the wear performance, maintenance of the mechanical strength is important, in order to avoid the fracture and delamination of TKA inserts.[1,11,12]
A relevant parameter for the definition of the mechanical strength is the tensile yield stress, i.e., the maximum tensile stress that the material can withstand without undergoing plastic deformation.
The crosslinking process improves the wear resistance of E-CROSS compared to conventional UHMWPE. As confirmed by laboratory tests, the presence of Vitamin E avoids the need for additional thermal treatments that may compromise the mechanical strength.[3, 7]
The GMK Sphere design optimizes the load distribution to reduce stress levels and to minimize polyethylene wear.[7]
GMK Sphere has a lower risk of polyethylene delamination and has less than half the average wear rate observed in other fixed bearing knee implants.[7, 13]
The GMK Sphere tibial insert in E-CROSS further improves the already excellent performance in terms of wear and delamination resistance of the GMK Sphere inserts.[7]
E-CROSS tibial inserts have been tested in a knee simulator and have shown a 21% polyethylene wear rate reduction when compared to UHMWPE inserts.[7]
The blending process prior to compression molding allows for a more uniform distribution of Vitamin E inside E-CROSS, and therefore a better control of the material‘s properties and oxidation resistance.[1, 6]
E-CROSS is not subjected to radiation during sterilization that could cause the formation of free radicals.[7, 8, 9]
E-CROSS is available for GMK Sphere and MOTO System.
[1] Doshi B. et al., «Fatigue Toughness of Irradiated Vitamin E/UHMWPE Blends», Journal Of Orthopaedic Research, pp. 1514-1520, September 2016.
[2] Oral E. et al., «Vitamin E diffused, highly crosslinked UHMWPE: a review», International Orthopaedics (SICOT), 35:215-223, 2011.
[3] Haider H. et al., «Does Vitamin E–Stabilized Ultrahigh-Molecular-Weight Polyethylene Address Concerns of Cross-Linked Polyethylene in Total Knee Arthroplasty?», The Journal of Arthroplasty, vol. 27, n. 3, pp. 461-469, 2012.
[4] Malito L. G. et al., «Material properties of ultra-high molecular weight polyethylene: Comparison of tension, compression, nanomechanics and microstructure across clinical formulations», Journal of the Mechanical Behavior of Biomedical Materials, pp. 9-19, 2018.
[5] Bracco P. et al., «Stabilisation of ultra-high molecular weight polyethylene with Vitamin E», Polymer Degradation and Stability 92, pp. 2155-2162, 2007.
[6] Oral E. et al., «Characterization of irradiated blends of α-tocopherol and UHMWPE», Biomaterials 26, pp. 6657-6663, 2005.
[7] Medacta: data on file.
[8] Kurtz S M, et al.“Postirradiation aging affects stress and strain in polyethylene components”, Clin Orthop, 350:209, 1998.
[9] White et al., “Effects of sterilization on wear in total knee arthroplasty”, Clin Orthop, 331:164-71, 1996.
[10] Lerf R. et al., «Use of vitamin E to protect cross-linked UHMWPE from oxidation», Biomaterials 31, pp. 3643-3648, 2010.
[11] Kondo et al., «Arthroscopy for evaluation of polyethylene wear after total knee arthroplasty», J Orthop Sci, vol. 13, pp. 433-437, 2008.
[12] Lu et al., «Wear pattern analysis in retrieved tibial inserts of mobile-bearing and fixed bearing total knee prostheses», Vol. 292-B, pp. 500-7, 2010.
[13] Haider H., “Tribological assessment of UHMWPEs”. In: Kurtz SM, editor. UHMWPE Biomaterials Handbook. 2nd ed. Academic Press; 2009; p. 381
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