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How plastics help define medical design excellence in 2014: Persona Knee System

The Persona Personalized Knee System from Zimmer Inc. (Warsaw, IN) is designed to minimize patient compromises that are part and parcel of standard knee systems and support advanced levels of personalization. It does so through a number of "intelligent instrument technologies," says Zimmer, along with proprietary advances in orthopedic technologies, including antioxidant protection from its Vivacit-E vitamin-E highly crosslinked polyethylene (PE) bearing surfaces.

The Persona Personalized Knee System from Zimmer Inc. (Warsaw, IN) is designed to minimize patient compromises that are part and parcel of standard knee systems and support advanced levels of personalization. It does so through a number of "intelligent instrument technologies," says Zimmer, along with proprietary advances in orthopedic technologies, including antioxidant protection from its Vivacit-E vitamin-E highly crosslinked polyethylene (PE) bearing surfaces.

"Zimmer's new premium polyethylene, Vivacit-E, optimizes the key qualities of wear, oxidative stability, and mechanical strength for long-term performance," explains Melinda S. Peiserich, Senior Engineer–Research for Zimmer. Conventional gamma-sterilized ultrahigh-molecular-weight PE is also available for the device, but Vivacit-E "eliminates compromises that were made with previous-generation crosslinked polyethylenes, namely a reduction in strength in order to achieve oxidative stability," says Peiserich. The advantages over a conventional PE bearing surface, she adds, are a 10% increase in in strength and 96% reduction in wear. Compared with Zimmer's previous highly crosslinked PE, wear is reduced by 73%.

Persona Knee System, Zimmer

The Vivacit-E process involves blending vitamin E into the PE resin, followed by compression molding and high-dose E-beam radiation to crosslink the PE and graft the vitamin E to the PE chain, explains Peiserich. Grafting vitamin E to PE ensures that it will not leach from the material during implant use.

Engineering studies were designed and performed to challenge the new-generation PE more than any of Zimmer's previous PE offerings, all with successful results, adds Peiserich.

The Persona system is one of five finalists in the Implant and Tissue-Replacement Products category of the 2014 Medical Design Excellence Awards. A ceremony at the MD&M East conference and exposition in New York City on June 11, 2014, will reveal the recipients of gold, silver, and bronze awards in this and the 10 other categories.

Click on the arrow below to learn about the material choices that were made for the MedCenter, a space-age prescription-drug-delivery system.

Norbert Sparrow

 

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