ma, inflammation, or infection, the disease is considered to be secondary. In most cases, however, osteoarthritis is primary, as no significant preceding event or condition can be identified (Swedberg & Stenbauer, 1992, p. 558). One precocious form of primary osteoarthritis has been shown to be inherited as a mendelian dominant disorder through one allele of the gene for type II procollagen (Knowlton, Katzenstein, & Moskowitz, 1990, p. 526).
Radiographically, the earliest signs of osteoarthritis are localized loss of joint space and subchondral sclerosis. As the condition progresses, ostephytes, subchondral cysts with sclerotic margins, and intra-articular osseous bodies may become evident. Finally, subchondral bony collapse may result from the compression of weakened and deformed trabeculae (Swedberg & Stenbauer, 1992, p. 559).
Histologically, the disease progression seen in radiographs corresponds to fibrillation, softening and erosion of cartilage, followed by bony proliferation at joint margins and at the base of fi
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