Effect of resin type and manufacturing method on wear of polyethylene tibial components.

The purpose of this study was to examine the effect of ultrahigh molecular weight polyethylene resin type and manufacturing method on wear of Miller-Galante I and II tibial knee components. Thirteen Miller-Galante I and 10 Miller-Galante II components were retrieved at revision surgery. The Miller-Galante I tibial components were made by direct compression molding of Hi-fax 1900 resin and the Miller-Galante II tibial components were made by machining from ram extruded rod of GUR 415 resin. Both generations were gamma radiation sterilized in air. The Miller-Galante I retrievals had significantly more wear damage in the form of scratching and embedded metallic debris, whereas the Miller-Galante II retrievals had significantly more wear damage in the form of delamination. For the implants with an implantation time of 5 years or more, the Miller-Galante II polyethylene had a significantly greater maximum density value than did the Miller-Galante I polyethylene. Examination of thin sections of the Miller-Galante II components revealed that delamination occurred through a subsurface region of severely oxidatively degraded polyethylene; no such subsurface degraded region was observed for the Miller-Galante I components. The results of this study suggest that delamination of polyethylene tibial components that have been gamma radiation sterilized (in air) is influenced by resin type or manufacturing method or both.