Combination of growth factors inhibits bone ingrowth in the bone harvest chamber

Previous studies using bone harvest chambers have shown that bone morphogen etic protein-2 inhibits bone ingrowth. The authors hypothesized that the co mbination of bone morphogenetic protein-2 and a potent angiogenic factor, b asic fibroblast growth factor, would result in increased bone formation in this model, Five New Zealand White rabbits were surgically implanted with b one harvest chambers in the proximal metaphyseal region of both tibias. The right leg of each rabbit was implanted with a bovine collagen sponge that was impregnated with recombinant human bone morphogenetic protein-2, basic fibroblast growth factor, or a combination of these factors. The left leg c hamber was implanted with the collagen sponge with no growth factors as a c ontrol. The bone that grew into the chambers was harvested after 2 weeks, a nd histomorphologic analysis was performed to determine the amount of tissu e and bone ingrowth. The tissue chambers were left empty for 2 weeks betwee n test implants, and this tissue also was harvested, analyzed, and compared with the other samples. The results showed decreased bone formation for th e bone morphogenetic protein-2, basic fibroblast growth factor, and combina tion of bone morphogenetic protein-2 and basic fibroblast growth factor tre ated groups when compared with the control and empty groups. The combinatio n of bone morphogenetic protein-2 and basic fibroblast growth factor showed inhibition of bone formation that was greater than either growth factor in dividually. The reason for the inhibition of bone formation with the combin ation of factors is unknown.