IN-VIVO EVALUATION OF RECOMBINANT HUMAN OSTEOGENIC PROTEIN (RHOP-1) IMPLANTS AS A BONE-GRAFT SUBSTITUTE FOR SPINAL FUSIONS

Study Design. Posterior spinal fusion segments were evaluated in adult mongrel dogs at 6, 12, and 26 weeks post-implantation. Four sites on each animal received implants consisting of recombinant human osteogen ic protein-1 on a bone collagen carrier, bone collagen carrier alone, autogenous iliac crest bone, or no implant material. Objective, To det ermine the efficacy of recombinant human osteogenic protein-1 as a bon e graft substitute in achieving posterior spinal fusion and compare th e results to those obtained using autogenous bone graft. Summary of Ba ckground Data. Posterior spinal fusion generally includes onlay grafti ng of autogenous or allogeneic bone after decortication of bony surfac es of the vertebral elements. The search for an acceptable bone graft substitute material has in recent years centered upon proteins capable of inducing bone in vivo. Recombinant human osteogenic protein-1 has demonstrated efficacy in healing large segmental osteoperiosteal defec ts in rabbits, dogs, and monkeys and appears ideally suited as a bone graft substitute for spinal fusions. Methods. The quality of fusion an d new bone formation was evaluated using plain films, computed tomogra phy, and magnetic resonance imaging. Results. Radiographic and histolo gic studies demonstrated that recombinant human osteogenic protein-1-t reated fusion segments attained a stable fusion by 6 weeks post-implan tation and were completely fused by 12 weeks. The autograft sites demo nstrated fusion at 26 weeks post-implantation. Conclusions, The result s indicated that recombinant human osteogenic protein-1 is an effectiv e bone graft substitute for achieving stable posterior spinal fusions in a significantly more rapid fashion than can be achieved with autoge nous bone graft.