IN-VIVO OF DEMINERALIZED BONE-MATRIX AS A BONE-GRAFT SUBSTITUTE FOR POSTERIOR SPINAL-FUSION

Study Design. Posterior lumbar spinal fusion segments were evaluated i n 9 adult mongrel dogs 6, 12, and 26 weeks after implantation. Four si tes on each animal received implants consisting of demineralized bone matrix alone, demineralized bone matrix with allograft bone, allograft bone alone, and autograft bone. Each unilateral fusion spanned one mo tion segment with one intervening vertebral level left undisturbed usi ng T13-L7. The fusions were evaluated radiographically, mechanically, and histologically. Objective. The purpose of this study was to determ ine the efficacy of demineralized bone matrix as a bone graft substitu te for stable posterior spinal fusion. Summary of Background Data. Pos terior spinal fusion is a procedure commonly performed for spinal stab ilization. Increasing the incidence and speed of stable spinal fusion is a primary goal in spinal surgery. Concerns have developed regarding the graft material used to induce bone healing at the fusion site. Th e advent of osteoinductive materials, such as demineralized bone matri x, may eliminate the need to harvest autograft bone and may circumvent the immunologic response and lower osteogenic potential associated wi th allograft bone. Methods. The quality of fusion and new bone formati on was evaluated radiographically using plain films, computed tomograp hy, and magnetic resonance imaging. After the dogs were killed, each f usion segment was evaluated mechanically in torsion to determine stiff ness and histologically to determine qualitative parameters of new bon e formation and remodeling. Conclusions. The results indicate that dem ineralized bone matrix alone or with allograft bone is ineffective; in achieving stable posterior spinal fusions. Results. Radiographic stud ies showed that autograft bone sites achieved stable fusion by 26 week s after surgery. Conversely, the demineralized bone matrix alone and w ith allograft bone demonstrated some new bone formation at 6 and 12 we eks, but did not achieve fusion by 26 weeks. The fusion sites of allog raft bone alone showed minimal new bone formation at all time periods. Mechanically, the autograft fusion sites demonstrated torsional stabi lity that was significantly greater than that of all other fusion site s at all time periods. The remaining fusion sites showed equivalent to rsional stiffness at all time periods. Histologic analysis confirmed t he radiographic and mechanical findings.