The induction of bone in organizing haematomata in rats.

The induction of ectopic bone formation has been described in a wide range of experimental systems. This lias emphasized the fact that undifferentiated osteogenic precursor cells persist in post foetal life after embryonic differentiation has ceased. A key observation in the studies on the transformation of these cells into osteoblasts was made by Urist [1965] when he discovered that the decalcified organic matrices of bone and dentine had osteoinductive properties. This phenomenon is attributed to the physicochemical effect of an inductor present in these matrices which induces competent mesenchymal cells to differentiate into osteoblasts [Urist et al., 1967]. The osteogenetic competence of mesenchymal cell populations was shown to be restricted in post-foetal life to specific areas of the body and in these areas mesenchy­ mal cells showed dilferent levels of readiness to differentiate into bone in response to implants of decalcified allogenic bone matrix (D.A.B.M.) [Urist et a!., 1967]. The use of an induction system to assist refractory skeletal regeneration is dependent upon it being able to initiate osteogenesis and maintain it until bone continuity is restored. Extraskeletal implants of D.A.B.M. however become encapsulated in fibrous connective tissue soon after implantation and this forms a barrier which confines the yield of induced bone to the limits of the enclosed matrix [Urist, 1965], The rapid unrestricted ingrowth of woven bone into organizing fracture haematomata suggested that the cell population in granulation tissue may provide a favourable environment for bone induction. This study was undertaken to determine whether implants of D.A.B.M. would induce osteogenesis in the granulation tissue of organizing haematomata held in perforated silicone rubber chambers implanted subcutaneously in rats.