Oxidation and fusion defects synergistically accelerate polyethylene failure in knee replacement.

We have previously reported upon a cohort of patients with premature failure of such material and postulated upon the impact of abnormally high concentrations of type 2 fusion defects whereby there is a lack of particle cohesion due to incomplete diffusion. In vivo oxidation has been purported to underscore the premature failure of polyethylene. The mechanism of such remains poorly delineated. New data has now been obtained by determining substrata oxidative profiles of 10 failed Kinemax Plus modular tibial insert analyses in conjunction with fusion defect detection. The full thickness of a series of cores was analysed using infra-red spectroscopy to identify higher levels of oxidation in loaded used material at both the articulating and non-articulating regions. A comparison was made to an unused control. Articulating, loaded, areas exhibited greater local concentrations of oxidised material and wider variation of such consistent with the higher presence of fusion defects. Subsurface analysis confirmed the presence of a major oxidative peak 2mm below the surface for all loaded areas irrespective of wear. Additionally we were able to identify a second major oxidative focus about halfway between the inferior (tibial baseplate) surface and the articulating area. We believe that the combination of high oxidation and fusion defects represents a second high stress zone consistent with the observation of tibial baseplate polyethylene dissociation and backside wear with resultant catastrophic material failure.