Long-term remodeling of vascularized and nonvascularized onlay bone grafts: A macroscopic and microscopic analysis

The present study was performed to compare vascularized and nonvascularized onlay bone grafts to investigate the potential effect of graft-to-recipien t bed orientation on long-term bone remodeling and changes in thickness and microarchitectural patterns of remodeling within the bone grafts. In two g roups of 10 rabbits each, bone grafts were raised bilaterally from the supr aorbital processes and placed subperiosteally on the zygomatic arch. The bo ne grafts were oriented parallel to the zygomatic arch on one side and perp endicular to the arch on the contralateral side. In the first group, vascul arized bone grafts were transferred based on the auricularis anterior muscl e, and in the second group nonvascularized bone grafts were transferred. Fl uorochrome markers were injected during the last 3 months of animal surviva l, and animals were killed either 6 or 12 months postoperatively. The nonva scularized augmented zygoma showed no significant change in thickness 6 mon ths after bone graft placement and a significant decrease in thickness 1 ye ar after graft placement (p < 0.01). The vascularized augmented zygoma show ed a slight but statistically significant decrease in thickness 6 months af ter graft placement (p < 0.003), with no significant difference relative to its initial thickness 1 year after graft placement. In animals killed 6 mo nths after bone graft placement, both the rate of remodeling and the bone d eposition rate measured during the last 3 months of survival were significa ntly higher in the vascularized bone grafts compared with their nonvascular ized counterparts (p < 0.02). By 1 year postoperatively, there were no sign ificant differences in thickness, mineral apposition rate, or osteon densit y between bone grafts oriented perpendicular and parallel to the zygomatic arch. These findings indicate that the vascularity of a bone graft has a si gnificant effect on long-term thickness and histomorphometric parameters of bone remodeling, whereas the direction of placement of a subperiosteal gra ft relative to the recipient bed has minimal effect on these parameters. In vascularized bone grafts, both bone remodeling and deposition are accelera ted during the initial period following graft placement. Continued bone dep osition renders vascularized grafts better suited for the long-term mainten ance of thickness and contour relative to nonvascularized grafts.