Effects of TGF beta on bone ingrowth in the presence of polyethylene particles

We implanted bone harvest chambers (BHCs) bilaterally in ten mature male Ne w Zealand white rabbits. Polyethylene particles (0.3 +/- 0.1 mu m in diamet er, 6.4X10(12) particles/ml) were implanted for two, four or six weeks bila terally in the BHCs, with subsequent removal of the ingrown tissue after ea ch 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 chamb ers containing TGF beta compared with those with particles alone (7.8 +/- 1 .3% v 16.9 +/- 2.7% respectively; 95% confidence interval (CI) for differen ce -14.0 to -4.30; p = 0.002), At four weeks, the percentage area of bone w as greater in chambers containing TGF beta compared with those with particl es 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 vit ronectin-receptor-positive cells (osteoclast-like cells) was greater in the treatment group with TGF beta compared with that with particles alone; mos t of these positive cells were located in the interstitium, rather than adj acent 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 manne r. Our data suggest that there is an early window at between two and six we eks, 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 obta ining osseointegration and bone ingrowth, especially in revisions when ther e is compromised bone stock and residual particulate debris.