Allogenic transplants of bone revascularized by microvascular anastomoses: A preliminary study

An area of experimental bone grafting that needs further study is the use of free vascularized allografts of bone. In 35 outbred mongrel dogs, the viability of vascularized bone allografts with and without azathioprine immunosuppression was compared to vascularized autogenous bone grafts. Viability was assessed by histologic techniques, fluorochrome bone labeling, and electron microscopy. Autogenous vascularized bone grafts remained viable, and it was concluded that microvascular technique was not the limiting factor in attaining survival of the grafts. The behavior of autogenous vascularized bone grafts with and without the influence of azathioprine was similar. Allogenic vascularized bone transplants uniformly failed at a period between 2 and 3 weeks. Immunosuppression with azathioprine did not appreciably affect survival of the osteocytes. However, the host response to the foreign tissue was slightly modified. The clinical ramifications of bone transplantations in humans are not analogous to the clinical situation of transplantation of other organs. If vascularized bone transplants are performed in humans, a relatively safe form of immunosuppression is necessary. This study suggests that azathioprine alone does not offer sufficient immunosuppression to insure viability of the vascularized transplant.