Characterization of Retrieved Total Ankle Replacement Liners

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This paper describes the failure analysis of two Total Ankle Replacement (TAR) devices where one device failed mechanically and the other device failed due to excessive wear and loosening. Optical and confocal imaging procedures were used to identify various failure modes. Fourier transform infrared spectroscopy was used to determine the oxidation index and crystallinity of the liners and compared them with values obtained for a shelf-aged liner which is used as a control. Regression equations were developed based on literature data to correlate oxidation index with strength of the material. 3D models of each liner were constructed to understand the damage modes at surface and sub-surface levels. Shear banding and embrittlement were observed for one of the failed liners. Both abrasive and adhesive wear were observed in the liners but they are not the dominant wear mechanisms unlike in other total joint replacement devices. Based on obtained results, the STAR™ (Scandinavian Total Ankle Replacement) device failed under higher shear and compression stresses at the bearing component resulting in fatigue-induced fracture due to higher torsion generated at the ankle joint. The Agility™ (DePuy) device showed lack of proper bony ingrowth resulting in clinical failure.



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