The correlation between fusion defects and damage in tibial polyethylene bearings.

Recent reports of fatigue failures of polyethylene tibial and patellar components have led to investigation of the role of design and material properties in these failures. Earlier investigations, concluding that high contact stress designs suffered greater damage in service, could not account for some of the fatigue failures. The current study hypothesizes that this failure is related to variations in the material properties of the polyethylene due to incomplete consolidation of the powder during manufacture, resulting in fusion defects. Retrieved polyethylene components and samples of polyethylene stock were examined to gain insight into the relationship between fusion defects, component failure, material forming processes, and powder grade. Statistically significant correlations (p < 0.05) were observed between the extent of defects and cracking, delamination, total wear damage, and duration in vivo. These correlations indicate that components manufactured from material with fusion defects may be less resistant to fatigue than components formed of fully consolidated material.