Bone Regeneration in Distraction Osteogenesis Demonstrates Significantly Increased Vascularity in Comparison to Fracture Repair in the Mandible

Background: Tissue analysis of bone regenerate has suggested an intense vascular response after mandibular distraction osteogenesis (DO). Quantifying and three-dimensionally imaging this vascular response could be of immense clinical import in efforts to advance the utility of bone regeneration and repair. Conventional quantification of vascular responses has heretofore focused on inexact, cumbersome measurements of blood flow and histologic vessel counting. Using micro-computed tomography after vessel perfusion, we posit that quantitative vascular metrics will be significantly higher in mandibular DO compared with those observed in fracture repair (FxR) after bony union. Methods: Sprague-Dawley rats underwent mandibular osteotomy and external fixator placement. A DO group (n = 9) underwent a 5.1-mm distraction, whereas a FxR group (n = 12) had a 2.1-mm fixed gap set. Forty days after surgery, Microfil was perfused into the vasculature, and imaging ensued. Vascular radiomorphometrics were calculated for the regions of interest. Independent-samples t-test was performed for comparison, with statistical significance set at P <= 0.05. Results: Stereological analysis demonstrated statistically significant increases in the distracted vasculature compared with fracture repair: vessel volume fraction (5.4% versus 2.8%, P = 0.030) and vessel number (0.86 versus 0.50 mm(-1), P = 0.014). Conclusions: We report robust and quantifiable increases in vascular density in DO compared with FxR. Our findings support a significant distinction between the regenerative processes of mandibular DO from the reparative mechanisms controlling fracture healing. A better understanding of the differences between the 2 types of bone formation may enable clinicians to selectively optimize therapeutic outcomes in the future.