Experimental vascularized bone transplantations

The postoperative hypertrophy of the vascularized fibula graft is of particular interest. In order to clarify the etiology of the hypertrophy, we conducted experimental projects on vascularized bone grafts using fluorochrome bone labelings, histomorphometry and measurement of blood flow in rats and rabbits. In the murine vascularized tibio-fibula graft for bone defects of the tibia, where mechanical stress to the graft can be expected, cross-sectional bone growth was maintained with acceleration of new bone formation and an alteration of growth direction at 3 weeks after the transplantation. In vascularized bone grafts where no mechanical stress to the graft is expected, more bone resorption was seen than bone formation. In the murine tail bone graft to a bony defect of the femur, the cancellous bone gradually disappeared, and the trabeculae took on an architecture characteristic of the femur. This process slowly transforms the graft into a femur with the morphologic features of a long bone. These results suggested that remodeling of the graft corresponding with the changes in the dynamic environment was accompanied by adequate resorption. The cross-age transplantation of vascularized tibio-fibula grafts in rats showed that the younger the donor, the faster the hypertrophy. Age is one of the important factors affecting remodeling of the vascularized bone graft. The blood flow of the grafted bone in the rabbits increased immediately after the transplantation as a reaction to surgery. Thereafter the blood flow of the graft may depend on the biological demands for new bone formation in adapting to the biomechanical environment of the recipient site.