BONE-FORMATION WITH USE OF RHBMP-2 - (RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2)

We examined the effect of rhBMP-2 (recombinant human bone morphogeneti c protein-2), delivered in a porous poly(DL-lactic acid) implant, on b one formation in a critical-sized defect in the radial diaphysis in ra bbits. A unilateral segmental defect, twenty millimeters long, was cre ated in the radius in ninety-six skeletally mature New Zealand White r abbits. Forty-eight rabbits were evaluated at four weeks and forty-eig ht, at eight weeks. Six groups were studied at each time-period. The d efect was left empty in one group (control), the defect was filled wit h an autogenous corticocancellous bone graft in one group, and the def ect was filled with a porous poly(DL-lactic acid) implant containing z ero, seventeen, thirty-five, or seventy micrograms of rhBMP-2 (one gro up each). Radiographs of the defects were made every two weeks. The pe rcentage of the total area of the defect that was radiopaque was deter mined with use of computerized radiomorphometry and this percentage wa s used as a quantitative measure of the extent of new-bone formation i n the defect, There were time and dose-dependent responses to rhBMP-2 for as long as four weeks; thereafter, the effects of seventeen, thirt y-five, and seventy micrograms of rhBMP-2 were independent of dose and time (p < 0.05). The defects that had been treated with either thirty -five or seventy micrograms of rhBMP-2 had a significantly greater (p less than or equal to 0.05) area of radiopacity than the defects that had been treated with either zero or seventeen micrograms of rhBMP-2. No significant difference could be found between the defects treated w ith thirty-five or seventy micrograms of rhBMP-2 and the defects fille d with an autogenous graft.