ENHANCEMENT OF BONE INGROWTH BY TRANSFORMING GROWTH-FACTOR-BETA

Enhancement of bone ingrowth with transforming growth factor-beta was evaluated in a canine model. Ten dogs had bilateral implantation of a titanium-fiber-metal-coated rod in the proximal part of the humerus. A three-millimeter gap between the outer surface of the porous coating and the surrounding cancellous bone was created to impair bone ingrowt h. All of the implants were plasma-flame-sprayed with hydroxyapatite a nd tricalcium phosphate. In each animal, one implant was also treated with recombinant transforming growth factor-beta 1 while the other imp lant, which was not so treated, served as a paired control. Two doses of transforming growth factor-beta 1 were used: 335 micrograms in five animals and 120 micrograms in the other five. At four weeks, the amou nt of bone ingrowth in the implants that had been treated with 120 mic rograms of transforming growth factor-beta 1 was threefold higher than that in the paired controls (p = 0.009), but with the numbers availab le there was no significant increase in bone ingrowth with the higher dose. The amount of new-bone formation in the three-millimeter gaps ad jacent to the treated implants was twice that in the gaps of the paire d controls, regardless of the dose. The differences between the treate d and control implants with regard to the architecture of the new bone in the gap indicate that the mechanism of action of transforming grow th factor-beta 1 may include both proliferation of osteoprogenitor cel ls and production of matrix by committed osteoblasts. Compared with th e findings in a previous study in which this canine model was used, th e data from the present investigation indicate that enhancement of bon e ingrowth in implants that have been treated with a combination of a hydroxyapatite-tricalcium phosphate coating and transforming growth fa ctor-beta 1 may exceed that obtainable with grafting of the gap with a utogenous cancellous bone.