Super CTPOD Wear Studies of Retrieved UHMWPE Components
Background. The objective of this study was to assess the suitability of using multi-directional pin-on-disk (POD) testing to characterize the wear behavior of retrieved ultra-high molecular weight polyethylene (UHMWPE).
Methods. The POD wear behavior of 25 UHMWPE components, retrieved after 10 years in vivo, was compared with 25 that were shelf aged for 10-15 years in their original packaging. Components were gamma sterilized (25-40 kGy) in an air or reduced oxygen (inert) package. 9-mm diameter pins were fabricated from each component and evaluated against wrought CoCr alloy using a Super-CTPOD with 100 stations under physiologically relevant, multi-directional loading conditions. Wear Testing Fluid (HyClone, UT) with a protein concentration of 20 g/L was used as a lubricant.
Results. Volumetric wear rates were found to vary based on the aging environment (i.e., shelf-aged or retrieved, in vivo), as well as sterilization environment (i.e. gamma air or gamma inert). Volumetric wear rates were lowest for the pins in the gamma inert, shelf aged cohort.
Conclusion. The results of this study support the utility of using modern, multidirectional POD testing with a physiologic lubricant as a novel method for evaluating the in vivo wear properties of retrieved UHMWPE components. The data also supported the hypothesis that wear rates of gamma-inert liners were lower than gamma-air liners for both retrieved and shelf aging conditions.
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