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 clinical 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 conventional UHMWPE and three HylamerTM-M tibial components of the same design and manufacturer. Samples of material were then obtained from the worn regions of each implant and subjected to mechanical characterization using the small punch test. Statistically significant relationships were observed between the metrics of the small punch test and the total damage score and the burnishing damage score of the implants. We also examined the near-surface morphology of the retrievals using transmission electron microscopy. TEM analysis revealed lamellar alignment at and below the wear surfaces of the conventional 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 behavior measured near the articulating surface. (C) 1999 Elsevier Science Ltd. All rights reserved.