EXPERIMENTAL SPINAL-FUSION WITH RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 WITHOUT DECORTICATION OF OSSEOUS ELEMENTS

Study Design. L4-L5 intertransverse process fusions were produced with 58 mu g, 230 mu g, or 920 mu g of recombinant human bone morphogeneti c protein-2 in 20 dogs. Eleven had traditional decortication of poster ior elements before insertion of the implant. Nine were left undecorti cated. All animals were evaluated 3 months after surgery. Objectives. To determine whether decortication is a prerequisite for successful fu sion in the presence of osteoinductive proteins such as bone morphogen etic protein-2. Summary of Background Data. Recombinant osteoinductive proteins can induce de novo bone in ectopic soft-tissue sites in the absence of bone marrow elements. Traditional methods for achieving spi nal fusion rely on exposure of bone marrow through decortication to fa cilitate osteogenesis. It is hypothesized that the presence of an impl anted osteoinductive protein obviates the need for exposure and releas e of host inductive factors. Methods. Recombinant human bone morphogen etic protein-2-induced intertransverse process fusions were performed with and without decortication. Fusion sites were evaluated by compute d tomography imaging, high-resolution radiography, manual testing, mec hanical testing, and histologic analysis. Results. One hundred percent of decorticated spines and 89% of undecorticated spines were clinical ly fused by 3 months. Ninety-one percent of decorticated spines and 78 % of undecorticated specimens exhibited bilateral transverse process o sseous bridging. The only spines that failed to achieve solid bilatera l arthrodesis were in the lowest dose group. With the higher two doses , there was histologic evidence of osseous continuity between the fusi on mass and undecorticated transverse processes. Conclusions. There we re no statistical differences in clinical and radiographic fusion rate s between decorticated and undecorticated sites. With higher doses of recombinant human bone morphogenetic protein-2, there was little histo logic distinction between fusions in decorticated versus undecorticate d spines.