Prolonged inflammatory reactions induced by artificial ceramics in the rat air pouch model

The male Sprague-Dawley rat subcutaneous air pouch was used to study the inflammatory potential of artificial ceramics that are used in joint replacement surgery. Local leukocyte influx, proteinase, prostaglandin E2 (PGE2) and tumor necrosis factor (TNF) levels were measured after injection of hydroxyapatite type I ceramic (HAP), tricalcium phosphate ceramic (TCP) and apatite-wollastonite glass ceramic (GC) into the pouch. Synthetic monosodium urate crystals (MSU) were used as positive controls and normal saline (NS) was a negative control. The response was monitored over 168 h by irrigating the pouch with 5 ml of NS and withdrawing 4 ml. MSU produced the greatest response in leukocyte counts, proteinase and PGE2, whereas HAP, TCP and GC elicited less response. The peak response with HAP, TCP and GC often appeared later than with MSU. TNF activity was significantly detected only after ceramics and not after MSU. The chronic and relatively prolonged reaction to some ceramics suggests that an inflammatory reaction may be seen after human implantation of these ceramics. The increased levels of TNF and production of PGE2, which is one substance proposed to contribute to bone lysis associated with loosening, are of special interest.