Mesenchymal Stem Cell Derived Osteogenic Cells Is Superior to Bone Marrow Aspirate Impregnated Biomaterial Complex in Posterior Spinal Fusion

The limited source of autograft has prompted extensive research on bone substitute and biological enhancement of the fusion mass in spinal fusion. Biomaterials impregnated with bone marrow aspirate has been applied to spinal fusion surgery. In this study, the effect of stem cell therapy in enhancing posterior spinal fusion was compared with the bone marrow aspirate method in a standard rabbit model. Bone marrow was aspirated from rabbit proximal femur (BMA group, n=6) and loaded on β-tricalcium phosphate ceramics (β-TCP) in excess. The composite was then implanted onto L5 and L6 transverse processes of the same animal in posterior spinal fusion operation with decortication on the same day. For stem cell therapy group, mesenchymal stem cells (MSCs) were isolated from bone marrow aspirate by adherence on plastic culture-ware. The MSCs were treated with osteogenic supplements (OS) during ex vivo cell expansion (MSC group, n=6). The osteogenic cells were seeded on β-TCP ceramics and cultured for one day. The cell-ceramics composite was implanted into the same rabbit as BMA group. The ceramics acted as control (n=6). Three fluorochromes, tetracycline, xyelonol orange and caclein were injected at week 2, 4 and 6 sequentially. The spinal segments were harvested at week 7 post-operation. The manual palpation of vertebral joint was assesses for solid fusion. The gap distance of inter-transverse process was measured by microCT and the bone mineral content (BMC) and volume of transverse processes by peripheral quantitative computed tomography. The specimens were undergone undecalcified histological analysis. The mineralization process was examined by fluorescent microscopy. By manual palpation, 50% of MSC group samples were found to have solid fusion in comparison with the incomplete fusion observed in the BMA and control group. The gap distance of inter-transverse processes in MSC group was the shortest. The volume of the transverse processes in MSC group was significantly greater than BMA and control group by 16% and 26% respectively. The BMC of transverse processes in MSC group was 40% greater than control (p<0.05) and 8% greater than BMA group. In fluorescent microscopy, both green fluorescent signal (labeled at week 6) and orange fluorescent signal (labeled at week 4) were observed in MSC group compare with the predominantly green fluorescent signal in the BMA group. In conclusion, the augmentation of MSC derived osteogenic cells is superior to bone marrow aspirate in rabbit posterior spinal fusion.