Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement.

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Abstract
Wear particles from thirty-five membranes obtained during revision hip-replacement operations were studied after digestion of the soft tissue with papain. The particles were isolated and were characterized with use of light and scanning electron microscopic techniques, x-ray microanalysis, and an automated particle analyzer. The mean size of the polyethylene particles was 0.5 micrometer, and the metal particles were a mean of 0.7 micrometer, as determined with scanning electron microscopy. 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 control samples. X-ray microanalysis revealed metal debris in sixteen (46 per cent) of the thirty-five membranes after digestion. Thirteen (50 per 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 one of the twelve membranes surrounding a titanium-alloy stem without a porous coating, compared with twelve of the fourteen membranes surrounding a titanium-alloy stem with a porous coating. This tenfold difference in prevalence was significant (p < 0.005). On the average, the total number of particles (expressed in millions per gram of tissue) associated with the bipolar acetabular components was twice that associated with the fixed acetabular components. In addition, there was a trend toward a larger mean size of the polyethylene particles in association with the bipolar cups. Our data indicate that particulate prosthetic debris in the tissues around failed femoral components that have been inserted without cement constitutes a class of particles that are predominantly less than one micrometer in size and are present in amounts of more than one billion particles per gram of tissue. Routine histological methods did not detect this class of wear debris and led to a gross underestimation of the amount of debris in these membranes.