EFFECTS OF PARTICULATE HIGH-DENSITY POLYETHYLENE AND TITANIUM-ALLOY ON TISSUE INGROWTH INTO BONE HARVEST CHAMBER IN RABBITS

The purpose of this study was to determine whether small, phagocytosab le particles of titanium alloy (Ti) and high-density polyethylene (HDP E) have an adverse effect on bone ingrowth. The bone harvest chamber ( BHC) was implanted bilaterally in the proximal tibial metaphysis of si x mature rabbits. The BHC has a transverse 1-mm wide pore providing a continuous canal through the chamber for tissue ingrowth. After an ini tial 6-week period for osseointegration of the BHC, the contents of th e canal mere harvested repeatedly at 3 weekly intervals. This could be done with the chamber in place, without disturbing its exterior surfa ce or the surrounding bone. The carrier solution, 1% sodium hyaluronat e (Healon),vas implanted first. In subsequent implantations, Healon wa s mixed with particles of HDPE or Ti averaging 4.7 +/- 2.1 and 3.0 +/- 2.6 mu m, respectively. The contralateral chamber was left empty and served as a control. The chambers were harvested repeatedly, alternati ng experimental and control sides. The sections from the control side, and those containing Healon alone demonstrated extensive trabecular b one in a fibrovascular stroma. The sections containing Ti alloy partic les were qualitatively and quantitatively similar to the control secti ons and those containing Healon, except for the presence of small blac k granules of Ti alloy, dispersed in the fibrovascular stroma or phago cytosed by scattered macrophages. The sections containing HDPE particl es were infiltrated and engulfed by mononuclear and multinuclear histi ocytic tells in a highly fibrous stroma. The majority of the multinucl eated cells present were interpreted as being foreign body giant cells . Less trabecular bone was seen in the HDPE group compared to the othe r groups. Using the parameters chosen for this experiment, it would ap pear that small, phagocytosable HDPE particles are more deleterious to net formation of bone compared to particles of Ti alloy. (C) 1995 Joh n Wiley and Sons, Inc.