Effects of TGFβ on bone ingrowth in the presence of polyethylene particles

We implanted bone harvest chambers (BHCs) bilaterally in ten mature male New Zealand white rabbits. Polyethylene particles (0.3 +/- 0.1 mu m in diameter, 6.4X10(12) particles/ml) were implanted for two, four or six weeks bilaterally in the BHCs, with subsequent removal of the ingrown tissue after each treatment. In addition to the particles, one side also received 1.5 mu g of recombinant transforming growth factor B1 (TGF beta 1). At two weeks, the bone area as a percentage of total area was less in chambers containing TGF beta compared with those with particles alone (7.8 +/- 1.3% v 16.9 +/- 2.7% respectively; 95% confidence interval (CI) for difference -14.0 to -4.30; p = 0.002), At four weeks, the percentage area of bone was greater in chambers containing TGF beta compared with those with particles alone (31.2 +/- 3.4% v 22.5 +/- 2.0% respectively; 95% CI for difference 1.0 to 16.4; p = 0.03), There were no statistical differences at six weeks, despite a higher mean value with TGF beta treatment (38.2 +/- 3.9% v 28.8 +/- 3.5%; 95% CI for difference -4.6 to 23.3; p = 0.16), The number of vitronectin-receptor-positive cells (osteoclast-like cells) was greater in the treatment group with TGF beta compared with that with particles alone; most of these positive cells were located in the interstitium, rather than adjacent to bone. TGF beta 1 is a pleotropic growth factor which can modulate cellular events in the musculoskeletal system in a time- and concentration-dependent manner. Our data suggest that there is an early window at between two and six weeks, in which TGF beta may favourably affect bone ingrowth in the BHC model. Exogenous growth factors such as TGF beta may be a useful adjunct in obtaining osseointegration and bone ingrowth, especially in revisions when there is compromised bone stock and residual particulate debris.