Jp. Collier et al., OVERVIEW OF POLYETHYLENE AS A BEARING MATERIAL - COMPARISON OF STERILIZATION METHODS, Clinical orthopaedics and related research, (333), 1996, pp. 76-86
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.