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Friday, March 2, 2001

Study looks at cross-linking, osteolysis

Recent use of crosslinked UHMWPE is motivated by the desire to reduce the incidence of particulate-induced osteolysis. Wear resistance is typically determined by gravimetric weight loss in simulator testing.

However, investigators in scientific exhibit 62 say no correlation has been established between gravimetric measurements and the number or size of particles generated. They investigated the relationship and found that increased radiation level decreases both gravimetric wear rate and particle size. Particle size influences the relationship between particle number and wear volume.

"The number of particles generated during testing does not correlate with gravimetric wear measurements," the investigators said. "Particle size and count should be used to complement gravimetric wear measurements in joint simulation. The improvement of volumetric wear shown in hip simulator studies may not accurately predict the potential for reduction of osteolysis in vivo."

Hip simulator testing was conducted to 5 million cycles on cross-linked (5 Mrad gamma-irradiated), gamma-sterilized (2.5 Mrad) and EtO-sterilized liners. Wear particles were isolated by digesting test serum in acid followed by filtration through 0.05 micron filters. Debris was imaged using a SEM.

Crosslinked and gamma liners showed 93 percent and 49 percent reductions, respectively, in wear rates compared to EtO liners (2.6 vs. 19.4 vs. 38.4 mm3/Mcycles). The crosslinked liners generated 31 per-cent fewer particles than the EtO liners (6.9x1012 vs. 10x1012/Mcycles). The gamma liners generated 30% more particles than the EtO liners (13x1012 vs. 10x1012/Mcycles). The mean equivalent circular diameters for the crosslinked and gamma liners were 33 percent and 17 percent smaller, respectively, than for the EtO liners (0.12 vs. 0.15 vs. 0.18 microns).

The investigators are Michael D. Ries, MD, University of California, San Francisco; and Marcus L. Scott, MS, and Willard L. Sauer, MS, both of Smith & Nephew Richards, Inc.

Funding was provided by Smith & Nephew Richards, Inc.

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2001 Academy News March 2 Index A

Last modified 02/March/2001 by IS