Remelting of Highly Cross-linked Polyethylene Worn Under Laboratory Conditions

It has been suggested that apparent wear damage in highly cross-linked polyethylene acetabular liners can be removed with subsequent remelting of retrieved liners. To test this hypothesis, we remelted liners that had been previously tested under controlled laboratory conditions and that had experienced nonzero wear rates and visible wear damage. Five liner groups were examined: three with a range of irradiation doses without heat treatment, and two irradiated to 100 kGys, one with remelting, and the other annealing. All groups had been worn in a hip simulator under impingement conditions that produced nonzero wear rates and loss of machining marks. Each liner was cut into quadrants that were graded for wear damage before and after posttest remelting. Cross-linked liners not previously heat-treated lost all prior damage and all machining marks. Remelted liners and three of six annealed liners experienced only a slight return of machining marks at the interface of the burnished area and the remaining intact machining marks. Our experiments represent a severe wear case but demonstrate removal of material from the surface through measurable wear prevents the return of identifiable machining marks despite remelting.