Examining the influence of short-term implantation on oxidative degradation in retrieved highly crosslinked polyethylene tibial components.

Concerns remain regarding the oxidative resistance of highly crosslinked polyethylene (PE). The study investigated the in vivo performance of Durasul highly crosslinked PE by comparing the oxidation index, density, and percent crystallinity in the weightbearing and nonweightbearing region of retrieved components with unused time zero tibial components. Retrieved and unused Sulene conventional PE tibial components were examined for comparison and the effects of shelf age, in vivo duration, and ex vivo duration were also investigated. The oxidation index was not significantly different between unused time zero and retrieved Durasul PE components. Regression analysis data supported these findings in that neither shelf age, in vivo duration, nor ex vivo duration was a significant predictor of oxidation index in the retrieved Durasul PE components. In contrast, the retrieved conventional PE components had significantly greater oxidation index, density, and percent crystallinity compared with unused time zero PE components. Regression data suggested that in vivo and ex vivo duration, but not shelf aging, influenced the changes observed in the conventional PE components. These data also showed that in vivo loading did not significantly affect the oxidation index, density, or percent crystallinity in either the retrieved Durasul or conventional PE tibial components. This investigation demonstrates that changes in oxidation index, density, and percent crystallinity of retrieved Durasul PE components after short-term in vivo durations are likely not a clinical concern. These data should be used as a benchmark to compare with future studies examining the long-term oxidative resistance of Durasul highly crosslinked PE tibial components.

Surface damage analysis of retrieved highly crosslinked polyethylene tibial components after short-term implantation.

The use of highly crosslinked polyethylene (PE) in the knee remains controversial, because of reduced fatigue fracture properties of the material. The current study investigated postmelt surface damage as well as potential contributors to this damage in retrieved highly crosslinked PE tibial components, after short-term in vivo durations. Retrieved conventional PE tibial components were examined for comparison, as well as unused time zero highly crosslinked and conventional PE tibial components for inherent manufacturing surface characterization. Predominant surface damage modes on highly crosslinked PE components were machine mark loss and abrasion, while conventional PE components primarily had machine mark loss, abrasion, and delamination. In vivo duration, PE thickness, and conformity of the design were significant predictors of surface damage on retrieved conventional PE components. Donor weight and the conformity of the design were significant predictors of surface damage on retrieved highly crosslinked PE components. This retrieval data on highly crosslinked PE tibial components suggest that in vivo wear occurred, observed as postmelt surface damage. The highly crosslinked Durasul material examined in this retrieval study appeared to outperform the conventional PE components made from 4150 resin, ram-extruded and gamma-sterilized in air, but not the conventional components made from 1020 resin, compression molding and gamma sterilization in nitrogen. Early retrieval data of highly crosslinked PE tibial components are important to serve as a benchmark to be compared with future longer-term retrieval studies investigating whether surface damage translates to clinically relevant particulate wear debris generation and PE clinical performance.