ISOLATION AND CHARACTERIZATION OF WEAR PARTICLES GENERATED IN PATIENTS WHO HAVE HAD FAILURE OF A HIP-ARTHROPLASTY WITHOUT CEMENT

Wear particles from thirty-five membranes obtained during revision hip -replacement operations were studied after digestion of the soft tissu e with papain. The particles were isolated and were characterized with use of light and scanning electron microscopic techniques, x-ray micr oanalysis, and an automated particle analyzer. The mean size of the po lyethylene particles was 0.5 micrometer, and the metal particles were a mean of 0.7 micrometer, as determined with scanning electron microsc opy. The automated particle analyzer revealed a mean particle diameter of 0.63 micrometer (more than 90 per cent of all particles were less than 0.95 micrometer) and a mean of 1.7 billion particles per gram of tissue, compared with only 143 million per gram of tissue for the cont rol samples. X-ray microanalysis revealed metal debris in sixteen (46 per cent) of the thirty-five membranes after digestion. Thirteen (50 p er cent) of the twenty-six membranes surrounding a titanium-alloy stem contained metal particles, compared with three of the nine membranes surrounding a chromium-cobalt stem. Metal debris was present in only o ne of the twelve membranes surrounding a titanium-alloy stem without a porous coating, compared with twelve of the fourteen membranes surrou nding a titanium-alloy stem with a porous coating. This tenfold differ ence in prevalence was significant (p < 0.005). On the average, the to tal number of particles (expressed in millions per gram of tissue) ass ociated with the bipolar acetabular components was twice that associat ed with the fixed acetabular components. In addition, there was a tren d toward a larger mean size of the polyethylene particles in associati on with the bipolar cups. Our data indicate that particulate prostheti c debris in the tissues around failed femoral components that have bee n inserted without cement constitutes a class of particles that are pr edominantly less than one micrometer in size and are present in amount s of more than one billion particles per gram of tissue. Routine histo logical methods did not detect this class of wear debris and led to a gross underestimation of the amount of debris in these membranes. CLIN ICAL RELEVANCE: Characterization of wear particles, as performed in th e current study, will permit a better assessment and understanding of the biological response in vivo. Our data also demonstrate the relatio nship between the design features of implants and the generation of pa rticles. It is important for surgeons who perform joint-replacement op erations to be cognizant of factors that may influence the production of wear debris and thus affect the fixation of the implant and limit t he longevity of the reconstruction.