METAL WEAR PARTICLE CHARACTERIZATION FROM METAL ON METAL TOTAL HIP REPLACEMENTS - TRANSMISSION ELECTRON-MICROSCOPY STUDY OF PERIPROSTHETIC TISSUES AND ISOLATED PARTICLES

The less intense tissue reaction around metal on metal total hip repla cements (THRs) compared to metal on polyethylene (PE) THRs may be expl ained by the differences in the characteristics of metal wear particle s. In this study, transmission electron microscopy was used to study m etal wear particles that were either in situ in cells or had been extr acted from the cells by a new technique based on enzymatic tissue dige stion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearin g couples. Most of the CoCrMo wear particles were smaller than 50 nm ( range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE part icles. While even a small volume of metal wear will produce high numbe rs of particles, the apparently less severe local tissue reaction to m etal particles may be due to the possibility that corrosion, dissoluti on and dissemination of metal particles may result in fewer local biol ogical effects than the long term retention of PE particles in the per iprosthetic tissues. (C) 1998 John Wiley & Sons, Inc.