The specific aims of this application are to continue the investigation of factors influencing the principles of vascularized bone grafts. Currently available vascularized bone grafts used to reconstruct massive segmental bone loss in compromised beds following wide resections of malignant bone tumors, traumatic bony defects, and infected non-unions have significant limitations resulting from structural confirmation of the graft, and donor site morbidity. The central goal of this proposal is to utilize biosynthetic components (hydroxyapatite ceramic mold), osteoinductive principles and osteoprogenitor cells coupled with a vascularized pedicle to produce "a molded vascularized osteogenesis". The second goal of this proposal is to isolate bone marrow stromal osteoprogenitor cells, determine the appropriate degree of differentiation that maximizes osteogenesis in vivo and expand this to defined populations ex vivo prior to utilization in molded osteogenesis. Studies have been designed to isolate the characterize osteoprogenitor cells from rabbit marrow in vitro and utilize diffusion chambers to determine the appropriate level of contact with matrix host cells and to determine the effects of demineralized bone matrix and of growth factors on heterotopic bone regeneration. This vascularized molded bone graft will be used as an island graft or a free transfer and the healing and material properties of these grafts will be examined and compared to conventional bone grafts.