The cellular changes during osteogenesis in bone and bone marrow composite autografts.

Osteogenesis in and around autografts has been studied in the hope of identifying the osteoblast precursor. Fresh autografts of cortical bone with its constituent bone marrow were implanted into intramuscular sites in rats. The grafts were removed at intervals over a four week period and examined by light and electron microscopy. A chronological sequence of degenerative, reparative and differentiative events was found and described. The relative contributions of the host and graft components to post-grafting osteogenesis are discussed and the problem of the origin of the osteoblast cells is examined, taking into account present views about the interrelationships between skeletal connective tissue cells and their precursors. It is concluded that, in the investigation described, the presence of host granulation tissue was necessary for osteogenesis and it is postulated that osteoblast progenitor cells can arise from this granulation tissue, their differentiation along the osteogenic line being stimulated in some way by the presence of the graft bone.