A series of in vitro patella damage tests were developed using a knee simulator to investigate electron-beam-irradiated and -melted ultra-high molecular weight polyethylene and conventional ultra-high molecular weight polyethylene at the patellofemoral articulation. Three different simulations were created: (i) normal gait with optimal component alignment, (ii) stair climbing with optimal component alignment, and (iii) stair climbing with 4 degrees of femoral component internal rotation to simulate a component mallalignment condition. In the last two simulations, all patellae were artificially aged. In normal gait, the unaged conventional and highly crosslinked patellae demonstrated similar behavior. In both stair climbing tests, unlike the aged highly crosslinked components, the aged conventional patellae developed cracks by 2 million cycles. These results demonstrate the potential advantage of highly crosslinked polyethylene for the patella. (c) 2006 Wiley Periodicals, Inc.
