[Air pouch model in the rat for evaluating articular phlogogenic capacity of ceramics]

We used the joint air pouch model in rats to study the inflammation induced by three types of calcium phosphate biomaterial: 10 mg of synthetic hydroxyapatite (HA), a sintered ceramic made of hydrooxyapatite and phosphate tricalcium (BCP), and calcium phosphate in the form of a fibre extracted from a vitro-ceramic material (VPC). Histological examination was made after 48 hours. The most intense inflammatory reaction was observed with BCP: the thickness of the superficial stratified layer of synoviocyte-like cells doubled, interstitial fibrosis occurred and neovascularization with polymorphous inflammatory infiltration was seen. HA led to the same, though less intense, type of reaction. Discrete, variable, localized inflammation was seen with VPC and was limited to the areas where the calcium phosphate fibres rolled. Despite good bone tissue tolerance, intraarticularly, these biomaterials can lead to synovial inflammation. This phlogogenic action varies greatly depending on the microcrystals injected. The factors which might affect the joint inflammatory reaction, including the size and surface of the microcrystals, the crystallinity, pH and physical treatments (heat, compaction) should be further evaluated with precision.