MOLECULAR METHODS OF ENHANCING LUMBAR SPINE FUSION

OBJECTIVE: An optimal method for spinal fusion would induce rapid grow th of bone via an osteoconductive and osteoinductive implant. This stu dy examines the spinal fusion enhancement potential of some osteocondu ctive and osteoinductive biomaterials. METHODS: Four similar canines r eceived unilateral posterolateral fusions on the left side at T13-L1 a nd L4-L5 and on the right side at L2-L3 and L6-L7. The experiments wer e grouped as follows: Group A, autogenous bone harvested from the ilia c crest; Group B, autogenous bone and collagen; Group C, no implant; a nd Group D, autogenous bone, collagen, and recombinant human bone morp hogenetic protein-2. Radiographic assessment, three-dimensional comput ed tomographic volumetric analysis, and biomechanical testing were per formed at each level. RESULTS: For Groups A and B, the fusions demonst rated moderate bone formation at 6 and 12 weeks postoperatively. Group D fusions exhibited earlier and more dramatic increases in volume and radiodensity and eventually were comparable in size to the vertebral bodies. Average fusion volumes computed from three-dimensional compute d tomographic analysis were: Group A = 1.243 cc, Group B = 0.900 cc, G roup C = 0.000 cc, and Group D = 6.668 cc (P = 0.003 compared to Group A). Group D exhibited flexion and extension biomechanical properties much greater than controls. The addition of recombinant human bone mor phogenetic protein-2 consistently yielded the strongest fused segments and, on average, enhanced extension stiffness by 626% and flexion sti ffness by 1120% over controls. CONCLUSION: The most advantageous spina l fusion implant matrix consisted of recombinant human bone morphogene tic protein-2, autogenous bone, and collagen. Future investigators, ho wever, need to examine the appropriate quantities of the individual co mponents and clarify the efficacy of the matrix for the various types of spinal fusion approaches.