title: Hydroxyapatite deposition in articular cartilage by intra-articular injections of methylprednisolone. A histological, ultrastructural, and x-ray-microprobe analysis in rabbits.
abstract: The mineral deposits in rabbit articular cartilage induced by intra-articular injections of glucocorticoid were studied by light and electron microscopy, using histochemical techniques and x-ray-probe microanalysis. This study demonstrated that the mineral deposits consisted of hydroxyapatite crystals. The initial deposition of hydroxyapatite crystals was seen around degenerating chondrocytes, where a halo-like pericellular space contained a large amount of electron-dense amorphous material. The initial precipitation of the crystals with a low ratio of calcium to phosphorus and the subsequent growth of crystals were seen only on or within the electron-dense amorphous material until the crystals formed mature, calcified nodules. The electron-dense amorphous material frequently coexisted with proteoglycans and degenerated collagen fibers. Digestion studies using chondroitinase ABC, papain, or chloroform and methanol suggested that the electron-dense amorphous material consisted of some protein and a small amount of lipid. Matrix vesicles were rarely seen in the calcifying areas. In addition, there was a correlation between sulphur, calcium, and phosphorus in the calcifying areas, where the relative element concentrations were: S (estimation counts of sulphur) = -0.862 X (calcium counts) + 1.472 X (phosphorus counts) + 102.146. This study demonstrated that electron-dense amorphous material, proteoglycans, and degenerated collagen fibers are present in loci where the hydroxyapatite crystals are formed in articular cartilage.
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis; D002358:Cartilage, Articular / Q000473:pathology* / Q000648:ultrastructure; D017886:Durapatite; D004577:Electron Probe Microanalysis; D006651:Histocytochemistry; D006882:Hydroxyapatites / Q000032:analysis*; D007267:Injections; D007719:Knee Joint; D008775:Methylprednisolone / Q000008:administration & dosage*; D010003:Osteoarthritis / Q000378:metabolism / Q000473:pathology; D010758:Phosphorus / Q000032:analysis; D011817:Rabbits; D011897:Random Allocation; D013455:Sulfur / Q000032:analysis
chemical_list: D006882:Hydroxyapatites; D010758:Phosphorus; D013455:Sulfur; D017886:Durapatite; D002118:Calcium; D008775:Methylprednisolone