THE SIZE AND SHAPE OF PARTICULATE POLYETHYLENE WEAR DEBRIS IN TOTAL JOINT REPLACEMENTS

Osteolysis induced by wear particles has been recognized as one of the major causes of long-term failure in total joint replacements. Howeve r, little is currently known about the exact nature of particles, as t he particles are too small to be characterized by light microscopy. In this study, ultrahigh molecular weight polyethylene (UHMWPE) particle s retrieved from ten cases (six cemented and four uncemented) for Free man type conforming tibiofemoral total knee replacements (TKRs), three Charnley total hip replacements (THRs) and five Imperial College/Lond on Hospital double cup surface hip replacements for aseptic loosening were extracted using a high-performance method with ultracentrifugatio n and characterized by scanning electron microscopy. The equivalent ci rcle diameter (ECD) of all 18 cases ranged from 0.40 to 1.15 mu m (Mea n +/- SE = 0.70 +/- 0.05 mu m, median = 0.67 mu m). The aspect ratio w as 1.50 to 2.04 (Mean +/- SE = 1.75 +/- 0.04, median = 1.73), and roun dness was 1.24 to 2.34 (Mean +/- SE = 1.61 +/- 0.07, median = 1.65). T he numbers of particles were 5.2 x 10(8) to 9.17 x 10(10)/g tissue (Me an +/- SE = 1.42 x 10(10) +/- 5.41 x 10(9)/g tissue, median = 7.04 x 1 0(9)). The number of polyethylene (PE) particles/g tissue in TKRs was significantly larger than that in THRs (1.04 x 10(10)/g tissue and 2.1 6 x 10(9)/g tissue respectively, median. p = 0.03, Mann-Whitney U test ). Unstable fixation of the tibial PE component might account for the accumulation of a large number of PE particles in the interface tissue .