Evaluation of insoluble bone gelatin as a carrier for enhancement of osteogenic protein-1-induced intertransverse process lumbar fusion in a rabbit model

STUDY DESIGN: Postero-lateral lumbar fusion in a rabbit model was performed to compare the bone induction potential of autograft, insoluble bone gelatin (ISBG), osteogenic protein-1 (OP-1), and the combination of ISBG and OP-1. OBJECTIVE: To evaluate the efficiency of ISBG as a carrier/enhancer for OP-1 in a rabbit spinal fusion model. SUMMARY OF BACKGROUND DATA: OP-1 or recombinant human BMP-7 has been shown to be effective in inducing new bone formation in surgical applications such as spinal arthrodesis. However, the lack of an ideal carrier contributes to its associated comorbidities (e.g., uncontrolled bone growth, local inflammatory over-response, nonfusion) and limits its use clinically. METHODS: Adult New Zealand white rabbits (n = 32) underwent bilateral lumbar intertransverse process fusion procedures at L5 to L6 and were randomized to receive: (1) autograft; (2) ISBG; (3) OP-1; or (4) ISBG in combination with OP-1 (ISBG + OP-1). Spinal fusion masses were evaluated by manual palpation, biomechanical testing, radiographic assessment, microcomputer tomography scanning and histologic examination at 6 weeks after surgery. RESULTS: Treatment of ISBG + OP-1 resulted in higher spinal fusion rates (7 of 7, 100%) than that of autograft (3 of 7, 43%), ISBG (2 of 8, 25%), and OP-1 (2 of 7, 29%) based on manual palpation (P > 0.01). Greater fusion rates in the ISBG + OP-1 group were also evidenced by radiographic examination (P > 0.01), microcomputer tomography bone volume analysis (P > 0.01), and biomechanical testing (P > 0.05). Histologic assessment demonstrated that treatment of ISBG + OP-1 induces new contiguous bone formation in the interval between the transverse processes which was absent in the other groups. CONCLUSION: In this study, ISBG + OP-1 resulted in more effective lumbar intertransverse process fusion than autograft, OP-1 putty or ISBG alone. ISBG is capable of enhancing OP-1-induced bone formation.