The relationship between the clinical performance and large deformation mechanical behavior of retrieved UHMWPE tibial inserts

Many aspects of the proposed relationship between material properties and c linical performance of UHMWPE components remain unclear. In this study, we explored the hypothesis that the clinical performance of tibial inserts is directly related to its large-deformation mechanical behavior measured near the articulating surface. Retrieval analysis was performed on three conven tional UHMWPE and three HylamerTM-M tibial components of the same design an d manufacturer. Samples of material were then obtained from the worn region s of each implant and subjected to mechanical characterization using the sm all punch test. Statistically significant relationships were observed betwe en the metrics of the small punch test and the total damage score and the b urnishing damage score of the implants. We also examined the near-surface m orphology of the retrievals using transmission electron microscopy. TEM ana lysis revealed lamellar alignment at and below the wear surfaces of the con ventional UHMWPE retrievals up to a maximum depth of approximately 8 mu m, consistent with large-deformation crystalline plasticity. The depth of the plasticity-induced damage layer varied not only between the retrievals, but also between the conventional UHMWPE and HylamerTM-M components. Thus, the results of this study support the hypothesis that the clinical performance of UHMWPE tibial inserts is related to the large-deformation mechanical be havior measured near the articulating surface. (C) 1999 Elsevier Science Lt d. All rights reserved.