HEALING SEGMENTAL FEMORAL DEFECTS IN SHEEP USING RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN

A middiaphyseal, 2.5-cm osteoperiosteal segmental defect stabilized by plate fixation was created in the right femur of 17 sheep. Four treat ment groups were included: Group I, no implant; Group II, inactive bon e matrix; Group III, recombinant human bone morphogenetic protein (rhB MP-2) mixed with inactive bone matrix; and Group IV, autogeneic bone g raft. Three animals had early failure of fixation, and the remaining 1 4 were evaluated at three months after implantation. Radiographs showe d bony union of all defects treated with rhBMP-2 (six) and a lack of b ony union in the negative-control groups treated with no implant (thre e) and inactive bone matrix without BMP (three). Both defects treated with autograft healed. New bone formation in the defect sites treated with rhBMP-2 first appeared one month after implantation and had a mea n bending strength (expressed as a percentage of the contralateral fem ur) of 91% +/- 59% (mean +/- standard deviation) for defects treated w ith BMP-2, 77% +/- 34% for autograft, 9% +/- 8% for no implant, and 11 % +/- 7% for inactive matrix without BMP. Three sheep treated with rhB MP-2 had their fixation plates removed at four months and were followe d for one year. Their bone defect sites remained solidly healed one ye ar after the initial operation.