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.