Postdoctoral Research Fellow Johns Hopkins Medical Institute Baltimore, MD, US
Introduction: Lumbar spinal fusion is challenging due to high pseudoarthrosis rates. BMP-2 loaded on an acellular collagen sponge (ACS) requires high BMP-2 doses, often leading to potential deleterious side effects. Our laboratory developed BioMim, a unique bone graft with inorganic and organic components, to enhance fusion outcomes with lower BMP-2 doses. This study compares the BMP-2 delivery method using BioMim and BMP-2-releasing nanoparticles to standard delivery with an ACS.
Methods: Thirty-six male Sprague Dawley rats were assigned to six groups: 1)ACS+0.1µg BMP-2, 2)ACS+1.0µg BMP-2, 3)BioMim+0.1µg BMP-2, 4)BioMim+1.0µg BMP-2, 5)BioMim+0.1µg nanoformulation BMP-2, 6)BioMim+1.0µg nanoformulation BMP-2. All rats underwent L4-5 posterolateral facet joint fusion. Fusion was assessed with microcomputed tomography (µ-CT) and histology eight weeks post-surgery. Fusion was categorized as fused, partially fused or not fused where fusion was defined as continuous bone bridging across operated levels and partial fusion was defined as significant new bone formation without complete bridging. Fisher’s Exact Test was utilized to determine significant differences.
Results: None of the samples in groups one or five achieved fusion. In group two, 50% achieved partial fusion and 50% complete fusion; group three had 33.33% complete fusion, all samples in group four fused; group six showed 16.67% complete fusion and 16.67% partial fusion. Fisher’s Exact Test indicated that ACS+0.1µg BMP-2 had significantly lower fusion scores than groups 2, 3, and 4(p=0.002). ACS+1.0µg BMP-2 had significantly higher fusion scores than group 5(p=0.002), while BioMim+1.0µg BMP-2 had significantly greater fusion rates than BioMim+1.0µg nanoformulation BMP-2 (p=0.015).
Conclusion : Our study suggests that nanoformulation did not significantly impact fusion rates, possibly attributable to altered release kinetics with BioMim. Although BioMim demonstrated superior fusion compared to ACS at reduced BMP-2 doses, further research is necessary to optimize BMP-2 release from the nanoparticle, focusing on achieving lower doses and a more consistent release profile. Ongoing histological studies are evaluating the characteristics, quality, and vasculature of the new bone formed within the fusion masses.
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