Effects of blood supply on bone formation in experimental spinal fusion with skeletal stem cells

Abstract: Aims of this study was to assess the new bone formation, vascular density (VD) and their correlation in an experimental model of spinal fusion with skeletal stem cells (SSCs) loaded into a ceramic carrier. METHODS. 15 rabbits (group 1) had, on the right paraspinal bed graft, cultured SSCs loaded into a ceramic carrier (group 1 A); on the left side, a sham operation including a decortication of the transverse processes without any addition of graft material was performed (group 1B). Further 15 rabbits (group 2) had fresh bone marrow loaded into ceramic granules on the the right side (group 2A) and ceramic granules alone on the left side (group 2B). After 6 months animals were sacrificed and radiographic and semi-quantitative and quantitative histological analysis of the fusion mass was performed. Sections of the fusion mass were then immunolabelled for alpha-smooth muscle actin to assess the VD. RESULTS The Radiographic evaluation showed a solid fusion in 13 specimens of group 1A (87%), and, respectively, in 14 (93%) and 13 (87%) of those of group 2A and 2B. However, a complete fusion was not observed in any group on histologic analysis. Abundant newly formed bone was observed in the periapophyseal regions in 60% of cases while no bone formation was seen between transverse processes. Periapophyseal VD was significantly higher compared to interapophyseal region in all groups (p<0.05) and a significant correlation was found between newly formed bone and VD (p = 0,0009). CONCLUSIONS: Our experimental posterolateral spinal fusion model with SSCs showed that new bone formation is strictly correlated to the local blood supply. If the latter is not adequate, as between the transverse processes, SSCs are unlikely to survive and limited bone formation occurs.