Optical analysis of surface changes on early retrievals of highly cross-linked and conventional polyethylene tibial inserts

Retrieved tibial liners of highly cross-linked and conventional polyethylene were examined for articular and backside surface damage. Surfaces were graded for pitting, machine-mark loss, scratching, abrasion, delamination, and embedded debris. Whereas no difference existed in the damage score for the 2 groups, the highly crosslinked group showed significantly less elimination of machine marks. Wear, surface plastic deformation, or a combination, could account for the damage on these components. Only 1 of the highly crosslinked polyethylene inserts was available for destructive testing. That insert was melted to activate the shape memory, and thus differentiate, between wear versus plastic deformation. Nearly all changes on the articular and backside surfaces disappeared upon melting, and original machining marks reappeared, suggesting that the surface changes for that component were primarily the result of plastic deformation and not material removal.