[Healing of free vascularized bone allotransplants: optimizing by short-term immunosuppression and host-derived neovascularization].

BACKGROUND: Living bone allotransplants (ATs) currently require long-term immunosuppression (IS), but this is impractical for extremity-preserving procedures. An alternative method to maintain viability of the transplant uses host-derived neoangiogeneic vessels combined with short-term IS. MATERIALS AND METHODS: Diaphyseal femoral defects in Dutch-Belted rabbits were reconstructed with a free microvascular AT from New Zealand White rabbits. Additionally, a host-derived intramedullary pedicled fascial flap was placed and short-term IS administered to two of four groups. Neovascularization and bone healing were quantified by microangiography and a custom radiographic score. RESULTS: Bone ATs with perfused fascial flaps achieved bone healing equivalent to autotransplant controls, even when they received IS only until host-derived neoangiogenesis replaced the original perfusion. Vascularized ATs without this combination achieved significantly inferior results. SUMMARY: This rabbit model demonstrated that increased bone turnover allows good healing but may temporarily weaken the allotransplant. However, by the more intense replacement of the graft with host-derived cells, this process may, in the long-term, ultimately result in a better transplant than an avascular graft.