Effect of Freeze-Dried Allograft Bone With Human Basic Fibroblast Growth Factor Containing a Collagen-Binding Domain From Clostridium histolyticum Collagenase on Bone Formation After Lumbar Posterolateral Fusion Surgery in Rats

Study Design. An experimental study. Objective. To evaluate the effectiveness of freeze-dried bone allograft (FDBA) with basic fibroblast growth factor (bFGF) fused with the polycystic kidney disease domain (PKD) and the collagen-binding domain (CBD) of Clostridium histolyticum collagenase, for the acceleration of lumbar posterolateral fusion in rats. Summary of Background Data. Reports indicate bFGF is an effective growth factor with osteogenic potential for promoting bone regeneration, although its efficiency decreases rapidly following its diffusion in body fluid from the host site. We developed a bFGF fusion protein containing the PKD and the CBD of C histolyticum collagenase (bFGF-PKD-CBD), which markedly enhanced bone formation at a relatively low concentration when applied to the surface of rat femurs in a previous study. The potential of this novel protein to accelerate bone fusion in a rat model of lumbar posterolateral fusion has yet to be investigated. Methods. Bilateral L4-L5 posterolateral fusions were performed, using 150 mg of FDBA powder per side. A total of 20 male Sprague-Dawley rats weighing 200 to 250 g/each were divided into two groups of 10 rats: FDBA was incubated with either phosphate-buffered saline (control group) or 0.58 nmol bFGF-PKD-CBD (bFGF-PKD-CBD group) before fusion surgery. The effect of bFGF-PKD-CBD was estimated using radiographs, microcomputed tomography, and histology (hematoxylin-eosin and von Kossa staining). Results. Both grafted bone volume in the posterolateral lesion and the volume of new bone formation on the surface of laminae and spinal processes were significantly higher in the bFGF-PKD-CBD group than in the control group. Histologically, new bone formation and surrounding chondrocytes and fibroblasts were prominent in the bFGF-PKD-CBD group. Conclusion. FDBA infused with bFGF-PKD-CBD may be a promising material for accelerating spinal fusion, and the FDBA-based delivery system for localizing bFGF-PKD-CBD may offer novel therapeutic approaches to augment spinal fusion. Level of Evidence: N/A