VARIATION IN THE INFLAMMATORY PROPERTIES OF BASIC CALCIUM-PHOSPHATE CRYSTALS ACCORDING TO CRYSTAL TYPE

Objective, To determine the inflammatory potential of basic calcium ph osphate (BCP) crystals, which have been identified in human joints, Me thods, Hydroxyapatite, carbonate apatite, whitlockite, and octacalcium phosphate crystals were injected in rat air pouches, Volume and cellu larity of the exudate were measured, Physicochemical properties of the injected BCP crystals were determined, and correlations with the magn itude of induced inflammatory responses were sought, Results. Signific ant differences were observed among the volumes and white blood cell ( WBC) counts of the pouch exudates, based on the various crystal types used to induce inflammation, A strong correlation was demonstrated bet ween the specific surface (SS) area of the injected crystals and the a rea under the curve for induced WBC count versus time (R(2) = 0.88, P = 0.05), This correlation was observed for SS area values below 50 m(2 )/gm, but when SS area increased further, this parameter plateaued, An other parameter of inflammatory response was obtained by dividing the area under the curve figuring WBC counts versus time by the correspond ing SS area for each crystal type, This parameter increased linearly w ith the Ca:P ratio (R(2) = 0.97, P = 0.0003), Conclusion. The inflamma tory potential of BCP crystals appeared to vary according to crystal f eatures, SS area and the Ca:P ratio (which correlates with crystal sol ubility) influenced inflammatory properties, These results could expla in the variable clinical consequences of BCP deposits, and must be tak en into account in the choice of apatite ceramics for use as biomateri als.