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Saturday, March 18, 2000

Gamma sterilization in air degrades polyethylene bearing, according to study

Data indicate that sterilization method, pre-implantation shelf life and resin type have significant impacts on properties and performance of polyethylene bearings for total joint replacement, say researchers who developed scientific exhibit 47.

More than 2,000 retrieved polyethylene bearings were examined and rated for clinical wear damage and performance. Select retrievals and more than 100 never-implanted polyethylene bearings were analyzed to assess material properties.

Different resins (GUR412, GUR415, 1900), fabrication types (machined, direct compression molded) and sterilization methods (gamma sterilization in air, gamma sterilization in inert environments, EtO and gas plasma) were represented.

Oxidation levels (FTIR) and mechanical properties (tensile tests-UTS and elongation) were measured for select retrievals and all never-implanted bearings. Crosslink density (swell ratio) was measured for select samples.

The researchers concluded that gamma sterilization in air causes degradative changes (oxidation, mechanical property reduction, in vivo fatigue). All resin types are subject to this degradation, however, resin type does not affect the rate of degradation. Short pre-implantation shelf life correlates with better bearing performance for bearings sterilized by gamma in air. Barrier packaging was found to limit oxidation of gamma sterilized bearings prior to implantation. Gamma radiation sterilization resulted in a higher degree of cross-linking than do other sterilization methods, perhaps impacting wear resistance. All gamma sterilization samples appear to have mechanical properties that change with time. Components sterilized with nongamma sterilization methods appear stable, even after periods of up to 20 years in vivo.

As the industry moves to alternative sterilization techniques and new, more highly crosslinked polyethylene bearing materials, analysis of retrieved joint prosthesis will remain a critical part of assessing performance of total joint replacements.

The researchers, all of Dartmouth Biomechanical Engineering Center, Hanover, N.H., are Barbara H. Currier, ME, research engineer; Lauren S. Bargmann, MS, research engineer; Brian Bargmann, MS, research engineer; John Currier, MS, research engineer; John Collier, DE, professor of engineering; and Michael Mayor, MD, professor of surgery.

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2000 Academy News March 18 Index C

Last modified 24/February/2000 by IS