TISSUE INGROWTH AND DIFFERENTIATION IN THE BONE-HARVEST CHAMBER IN THE PRESENCE OF COBALT-CHROMIUM-ALLOY AND HIGH-DENSITY-POLYETHYLENE PARTICLES

Particulate wear debris from joint replacements has been implicated in the etiology of periprosthetic bone resorption. However, the effect o f high-density-polyethylene or cobalt-chromium-alloy particles on oste oclastic bone resorption in vivo has not been studied previously, to o ur knowledge. Therefore, we examined the effect of these particles on tissue ingrowth, net bone formation (per cent trabecular bone), and os teoclastic bone resorption (osteoclasts per unit of bone surface) with use of a bone-harvest chamber that had a transverse one-millimeter ch annel for tissue ingrowth. After an initial six-week period for incorp oration of the chamber into the proximal part of the tibia of rabbits, the contents of the channel were harvested repeatedly at three-week i ntervals. The carrier solution, 1 per cent sodium hyaluronate, was imp lanted first. In subsequent implantations, the hyaluronate was mixed w ith high-density-polyethylene or cobalt-chromium particles at concentr ations of 10(8) particles per milliliter. The tissue harvested from th e chambers that contained no particles was composed of longitudinally oriented trabecular bone in a fibrovascular stroma. Particulate high-d ensity polyethylene evoked a moderate foreign-body reaction and a chro nic inflammatory response and decreased net bone formation. When cobal t-chromium particles had been implanted, the tissue exhibited a more f lorid 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 t he amount of net bone formation and osteoclastic bone resorption in th e presence or absence of high-density-polyethylene or cobalt-chromium particles. The amount of bone was greatest in the control specimens, m oderately decreased in the presence of high-density-polyethylene parti cles, and greatly decreased in the presence of cobalt-chromium particl es. The number of osteoclasts in Howship lacunae per unit of trabecula r bone surface was increased in the presence of high-density polyethyl ene, indicating that these particles stimulate osteoclastic bone resor ption.CLINICAL RELEVANCE: Particles of polyethylene and cobalt-chromiu m alley are produced at the interfaces of total joint replacements. Pr evious studies have implicated particulate debris as a cause of peripr osthetic resorption of bone. The current in vivo study demonstrated th at phagocytosable polyethylene particles decrease net bone formation a nd increase the number of osteoclasts along bone surfaces. Cobalt-chro mium-alloy particles appear to decrease net bone formation by interfer ing with bone formation. These findings may be relevant to the ingrowt h of bone into porous-coated components, especially in revision proced ures in which the membrane is not thoroughly debrided, Wear debris may also affect the remodeling of bone around joint prostheses.