The Journal of Bone and Joint Surgery, Vol 68, Issue 4 509-520, Copyright © 1986 by Journal of Bone and Joint Surgery, Inc
Hydroxyapatite deposition in articular cartilage by intra-articular injections of methylprednisolone. A histological, ultrastructural, and x-ray-microprobe analysis in rabbits
T Ohira and K Ishikawa
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.
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