OVERVIEW OF POLYETHYLENE AS A BEARING MATERIAL - COMPARISON OF STERILIZATION METHODS

Polyethylene has been used for more than 30 years as an orthopaedic be aring material; however, there has been recent concern regarding the e arly failure of a small percentage of the polyethylene bearings. The d amage seen in some retrieved polyethylene components has been linked t o gamma radiation sterilization in air, which was widely used by the i ndustry for years. Gamma radiation in air has been documented to cause an increase in oxidation and degradation of mechanical properties wit h time. The degradation of polyethylene initiated by gamma sterilizati on in air has led the orthopaedic industry toward alternative steriliz ation methods, including gamma radiation in an inert gas or vacuum env ironment, ethylene oxide gas sterilization, and gas plasma sterilizati on. For many of these alternative techniques, little clinical performa nce data exist. This study is a comparative evaluation of sterilizatio n methods using the same analytic techniques that have been used to do cument the effects of gamma sterilization in air an polyethylene. Four ier transform infrared spectroscopy, electron spin resonance, and unia xial tensile testing are used to compare, respectively, the oxidation levels, free radical concentration, and mechanical properties of mater ial sterilized by each method. The polyethylene is evaluated before st erilization, poststerilization, and postartificial aging. All examined alternative sterilization methods, when compared with gamma steriliza tion in air, caused less material degradation during a component's pre implantation shelf life.