MORPHOLOGY OF DEBRIS FROM GAMMA CROSSLINKED-REMELTED POLYETHYLENE

Abstract

Crosslinking of UHMWPE markedly improves its wear resistance. However, Green et al. (JBMR 53, 490, 2000) have reported that the wear debris from crosslinked PE were smaller than from non-crosslinked PE, and that particles with a mean diameter of 0.24 μm diameter caused more osteolytic activity of mouse macrophages in vitro than 0.45 μm or 1.7 μm particles. In order to predict how a new PE will behave clinically, however, it is desirable to compare its particle morphology to that of the gamma-air sterilized PE that was used in the vast majority of acetabular cups over the past three decades. We compared PE wear debris that were generated in a hip simulator and recovered by digestion and filtration of the serum lubricants, from cups crosslinked at 2.7 Mrads in air (historical controls), and cups machined from extruded bars that had been pre-gamma crosslinked at 4.5 Mrads and remelted (to extinguish free radicals and stabilize against oxidation) prior to cup machining. The debris were 85% and 92% rounded particles, respectively, and the balance were fibrils. The diameters of most of the rounded particles were from 0.07 to 0.3 μm, with very similar distributions in this range for the two materials. The total number of round particles from the 4.5 Mrad remelted PE was 32% and 76% below that of the 2.7 Mrad gamma-air non-aged and aged cups, respectively, the number of fibrils was 66% and 88% lower, respectively, and the total volume of wear debris per million cycles was 71% and 90% lower with the 4.5 Mrad-remelted PE cups, respectively. Since there was little if any systematic change in particle morphology, the substantially reduced wear and high oxidation resistance of the cups fabricated from gamma crosslinked-remelted PE could markedly reduce the incidence of clinical osteolysis.