Effectiveness of anti-oxidant polyethylene: What early retrievals can tell us.

The optimum UHMWPE orthopedic implant bearing surface must balance wear, oxidation, and fatigue resistance. Antioxidant polyethylene addresses free radicals, resulting from irradiation used in cross-linking, that could oxidize and potentially lead to fatigue damage under cycles of in vivo use. This study evaluates what short-term antioxidant UHMWPE retrievals can reveal about: (1) oxidation-resistance and (2) fatigue-resistance of these new materials. Retrievals of three different antioxidant polyethylene materials (n = 25) were analyzed by FTIR and uniaxial tensile tests and compared to conventional (n = 20) and remelted highly cross-linked (n = 30) polyethylene retrievals of similar in vivo duration. Maximum oxidation values differed significantly across material types (p = 0.018). No antioxidant retrieval exhibited a subsurface oxidation peak, in contrast to conventional gamma-sterilized (55%) and highly cross-linked (37%) retrievals that exhibited subsurface oxidation peaks over the same in vivo time. Trans-vinylene index (TVI) correlated positively with nominal irradiation dose (p < 0.001). Tensile toughness correlated negatively with increasing TVI (p < 0.001). The antioxidant materials in this study prevented in vivo oxidation more effectively than remelted HXL polyethylene at least over the in vivo period represented. The comparison of antioxidant retrieval tensile properties can be used as a guide for clinicians in choosing appropriate materials for the applications represented by their patients.