Do rim cracks and backside grinding affect the aging kinetics of alumina-matrix composite acetabular liners?

The acetabular liner malalignment and rim impingement have been problematic issues in ceramic-on-ceramic (CoC) total hip arthroplasty (THA). Commercial ceramic liners made of alumina-matrix composite (AMC) have polished articulation and rim, and roughly ground backside with a button-like apical projection (post) to resist tilting. In this study, we hypothesized that rim cracks and backside grind critically affect the aging kinetics of tetragonal zirconia dispersed in AMC structure. We analyzed phase transformation in the zirconia phase and residual stresses in the alumina matrix during aging by Raman and fluorescence spectroscopy. We demonstrated that the polished surfaces showed environmental stability in vitro, while the roughly-ground backside showed a significant stability loss and tensile stress accumulation as a consequence of enhancing the inter-component fixation between the liner and the metallic shell. Rim cracking locally produced a preferential transformation at the tip and the surrounding of the crack. Note that the tensile stress concentration at the crack tip was counteracted by the phase transformation after a few hours of aging. This suggests the presence of a time lag in vivo before further transformation around the crack could provide a crack shielding effect in the material. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 791-798, 2019.