The Ectopic Osteoconduction Model - (Periosteum/Ha Composite Implantation At Subcutaneous Site)

Vascularlized rat periosteum was wrapped around porous hydroxyapatite ceramics (HA) and transferred to a rat subcutaneous site. The periosteum/HA composites were harvested 4 weeks post implantation and used for histological analysis. New bone formation was detected outside of HA (original location of the periosteum) as well as in the pore areas away from the location of periosteum. In the pore areas, the bone formation started on the HA surface and fibrous tissue interposition was not observed between thus formed bone and HA. The results imply that the osteogenic capacity of the periosteum engaged in the bone formation outside of the HA, whereas undifferentiated mesenchymal cells migrated from invading tissue into the pore areas initiated bone formation directly on the HA surface. These findings indicate the importance of the HA surface for osteoblastic differentiation and we propose the subcutaneous implantation of the composite as an ectopic osteoconduction model.