OSTEOGENESIS IN EXTRASKELETALLY IMPLANTED POROUS CALCIUM-PHOSPHATE CERAMICS - VARIABILITY AMONG DIFFERENT KINDS OF ANIMALS

Synthetic porous calcium phosphate ceramics (HA/TCP) were implanted in tramuscularly and subcutaneously in dogs, pigs, goats, rabbits and rat s, designed to make a comparative study of the host tissue responses t o porous HA/TCP ceramics in different kinds of animals. Specimens were harvested at 15, 30, 45, 60, 90 and 120 days after implantation. Deca lcified and undecalcified sections were made and examined by light mic roscopy. Obvious bone formation could be detected in some specimens ha rvested from dogs and pigs after 45 days intramuscular implantation or after 60 days subcutaneous implantation. At days 90 and 120, an exten sive amount of bone formed in all specimens implanted in dogs and pigs . However, no histologically detectable bone formation was observed in any specimen implanted intramuscularly and subcutaneously in goats, r abbits and rats until 120 days. It is demonstrated from this finding t hat the synthetic porous calcium phosphate ceramics are capable of ind ucing osteogenesis when implanted in non-bony sites, but this ability varies between different kinds of animals. Earlier periods of observat ion in specimens harvested from dogs showed that bone differentiation in the pore regions of the ceramics follows a complex process involvin g invasion of the fibrovascular connective tissues at day 15, appearan ce of polymorphic mesenchymal cells near the invading vasculature and at the interface with the ceramics at day 30, differentiation of osteo blasts and formation of bone matrix in direct contact with the surface of the ceramics at day 45, and finally remodelling of the fibrous con nective tissue into an extensive amount of bone at days 60, 90 and 120 . (C) 1996 Elsevier Science Limited