Experimental hydroxyapatite synovial and articular cartilage calcification: light and electron microscopic studies.

Intraarticular calciphylaxis with cartilage and synovial calcification was produced in rabbits by oral administration of a single dose of dehydrotachysterol followed by an intraarticular injection of ferrous chloride. Synovial membrane apatite deposits were seen in the interstitium, on collagen fibers, and within cell vacuoles. In contrast, long-term administration of dehydrotachysterol alone induced only articular cartilage calcification. Such calcification was limited to the mid and deep zone of cartilage. Most calcium deposits were apatite-like crystals. Acute crystal-associated inflammation was not demonstrated in these specimens with crystals sequestered in synovial or cartilage tissue. Further studies on these models will examine the relation of apatite to joint disease.