Knee simulator wear of polyethylene tibias articulating against explanted rough femoral components

Highly cross-linked and melted polyethylene tibial inserts have recently been introduced for clinical use to reduce fatigue damage and adhesive wear in tibial inserts. Other authors have studied the effect of counterface roughness on the wear behavior of polyethylene tibial inserts in knee simulators using femoral components that were roughened artificially. They reported a higher wear rate with highly crosslinked polyethylene than with unirradiated polyethylene tibial inserts. Artificial roughening of femoral components may not be clinically relevant. To evaluate this concern, we studied the wear behavior of highly cross-linked and conventional polyethylene tibial inserts articulating in vitro against surgically retrieved femoral components that had become roughened in vivo. The wear rate of the highly cross-linked polyethylene (5.9 and 6.8 mg/1 million cycles with 100 and 50% serum) was 80% lower than the wear rate of the conventional polyethylene (33.5 and 32.2 mg/1 million cycles with 100 and 50% serum) tibial inserts after 2 million cycles of simulated gait. This study suggests that during in vivo use, scratches that are generated on the femoral components are likely to produce a higher wear rate with both cross-linked and conventional polyethylene than a smooth femoral component, but that this wear rate is likely to be higher with conventional polyethylene than with highly cross-linked polyethylene tibial inserts.