NONCONSOLIDATED POLYETHYLENE PARTICLES AND OXIDATION IN CHARNLEY ACETABULAR CUPS

Nonconsolidated particles of ultra high molecular weight polyethylene are believed to be defects that adversely can affect the wear performa nce of total joint prostheses. The present study was done to determine the number, size, and distribution of these particles and to determin e if their presence correlated with wear performance, as well as with other clinical and implant parameters. Forty retrieved and 7 new, neve r-implanted acetabular components were examined using light microscopy on thin cross sections. Particles were found in 92% of retrieved comp onents and in all the new components. Particles in the retrieved compo nents were either randomly distributed (32 components) or banded (with particles localized in regions approximately 1 mm below the outer sur face of the component). No correlations were found between the number or area of particles and the wear performance or any of the clinical o r implant variables. The presence of particles in the new implants was found to correlate with the length of time since the components had b een radiation sterilized. For retrieved components, the density (and, therefore, the level of oxidative degradation) was high in the areas o f banded particles. For new components, the density was higher the lon ger the time since sterilization. Nonconsolidated polyethylene particl es are prevalent in total replacements but their source and cause are unknown. The results of this study show that they do not appear to aff ect or correlate with the length of implantation of acetabular cups. H owever, they still may be expected to adversely affect performance in cases where large numbers of particles are banded together near articu lating surfaces of high stress environments such as found in the knee.