Particulate wear debris from joint replacements has been implicated in
the etiology of periprosthetic bone resorption. However, the effect of
high-density-polyethylene or cobalt-chromium-alloy particles on
osteoclastic bone resorption in vivo has not been studied previously, to
our knowledge. Therefore, we examined the effect of these particles on
tissue ingrowth, net bone formation (per cent trabecular bone), and
osteoclastic bone resorption (osteoclasts per unit of bone surface) with
use of a bone-harvest chamber that had a transverse one-millimeter channel
for tissue ingrowth. After an initial six-week period for incorporation of
the chamber into the proximal part of the tibia of rabbits, the contents of
the channel were harvested repeatedly at three-week intervals. The carrier
solution, 1 per cent sodium hyaluronate, was implanted first. In subsequent
implantations, the hyaluronate was mixed with high-density-polyethylene or
cobalt-chromium particles at concentrations of 10(8) particles per
milliliter. The tissue harvested from the chambers that contained no
particles was composed of longitudinally oriented trabecular bone in a
fibrovascular stroma. Particulate high-density polyethylene evoked a
moderate foreign-body reaction and a chronic inflammatory response and
decreased net bone formation. When cobalt-chromium particles had been
implanted, the tissue exhibited a more florid foreign-body reaction and a
chronic inflammatory response, often in a nodular arrangement, in a
background of dense connective tissue. Bone was sparse, and areas of cell
necrosis and hyaline degeneration were noted. Histomorphometric analyses
were carried out to determine the amount of net bone formation and
osteoclastic bone resorption in the presence or absence of
high-density-polyethylene or cobalt-chromium particles. The amount of bone
was greatest in the control specimens, moderately decreased in the presence
of high-density-polyethylene particles, and greatly decreased in the
presence of cobalt-chromium particles. The number of osteoclasts in Howship
lacunae per unit of trabecular bone surface was increased in the presence
of high-density polyethylene, indicating that these particles stimulate
osteoclastic bone resorption.