Introduction: Highly crosslinked UHMWPEs have been widely used in total hip replacements but have seen limited use at the knee due to concerns over strength characteristics. A new process, sequential irradiation and annealing, overcomes these limitations.

Materials and Methods: GUR 1020 polyethylene was sequentially crosslinked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (SXL).

Wear was determined by weight loss under normal walking and stair climbing conditions (MTS knee simulator, 5 to 10 million cycles, 1 Hz, maximum load of 2600 N to 3800 N, alpha fraction bovine calf serum). Scorpio CR and PS knees were evaluated using SXL and UHMWPE gamma sterilized to 3 Mrad in nitrogen (gamma-N2). Oxidative challenge was in 5 atmospheres of oxygen at 70 degrees C for 14 days.

Results: Scorpio gamma-N2 CR knees under normal walking conditions had a weight loss of 32.6 +/− 1.9 mg/million cycles compared to 6.5 +/− 1.6 mg/million cycles for SXL (p of 0.024). With Scorpio PS knees, the wear was 33.5 +/− 1.6 for gamma-N2 versus 7.7 +/− 0.7 mg/million cycles for SXL (p of 0.000009) subject to stair climbing simulation. Wear particle size was similar for SXL and gamma-N2. SXL knees showed no effect of oxidative challenge in a 10 million-cycle knee study.

Discussion and Conclusions: Wear is reduced by 80 percent and 77 percent respectively for CR and PS knees with SXL compared to gamma-N2. SXL has high resistance to oxidative challenge as shown by the lack of effect on knee wear results.