In order to elucidate the healing process of vascularized bone grafts, a bone defect was prepared on the mandible of adult dog. Bone was taken from the tibia together with the nutrient saphenous artery and vein, and was grafted by microvascular anatomosis. A nonvascularized bone was grafted on the contralateral site as control, and the healing process was observed over time by H-E stained and fluorescent labeled specimens.
1. In the vascularized bone grafts, transient inflammatory changes were noted initially but subsided after 2 weeks. At the junction between the grafted and existing bone, there was some difference in the amount of bone formation, compared with the non-vascularized bone grafts. After 4 weeks, the morphology of the grafted cortical bone was maintained, and briding was noted at the junction. The graft bone and lateral region of underlying bone became transitional after 8 weeks. Furthermore, it became impossible to recognize the junction after 24 weeks, and almost no change was noted up to 48 weeks.
2. The bone grafts maintained their original morphology in the initial stage, but after 2 weeks, necrosis and resorption of bone occurred from immediately below the graft bone. After 4 weeks, bone formation was mostly derived from the underlying bone, and no bridging was defected. After 8 weeks, the graft bone itself was absorbed, and the new trabecular bone derived from the underlying bone circumscribed the grafted site. Furthermore, maturation of trabecular bone continued even after 24 weeks, and the morphology of cortical bone was found after 48 weeks.
3. In vascularized bone grafts, signs of labeling were recognized from immediately after the operation and became most remarkable after 4 weeks. However, after 8 weeks, slight signs of labeling image were merely seen at the junction. On the other hand, in the nonvascularized bone grafts, labeling was confirmed for the first time after 4 weeks, and continued up to 24 weeks.
4. The results suggest that vascularized bone grafts effectively adhered to the underlying bone without changing the outer from by maintaining the activity of the graft bone itself from immediately after the operation. On the other hand, non-vascularized bone grafts were gradually absorbed, finally providing the contour of the mandible, but required much more time for the bone remodeling process compared with the vascularized bone grafts.
