[Calcium phosphate ceramics in orthopedic surgery].

Calcium phosphate ceramics might replace bone grafts in orthopaedic surgery. The chemical determination of these materials is now well known, and world-wide animal experiments as well as our own experience have proven that these products are both biocompatible and bioactive. The early chemical and physico-chemical mechanisms of interaction between calcium phosphate ceramics and bone tissue and biological fluids at the site of implantation are numerous (degradation, dissolution, crystal precipitation). These processes precede the cellular mechanisms of osteogenesis which take place during contact with the materials and define osteoconduction. When implanted in a bony environment, the ceramic ensures the formation of a genuine bone which within a few months will acquire all the characteristics of a normal lamellated bone with areas of apposition and resorption during remodeling. However, the mechanical characteristics of calcium phosphate ceramics do not permit an early loading, and they should only be used to fill bone cavities. In vertebral arthrodesis they must be implanted in stress-free areas and combined with strong and stable appliances. To benefit from the special bioactivity of calcium phosphate ceramics, research workers are now turning towards the treatment of metal alloys or composite fibres surfaces as well as of calcium phosphate complexes and extracellular matrix constituents (collagen, proteoglycans, etc.).