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Synovial chondromatosis

Etiology: • Unknown.

Pathogenesis: • Appears to be a metaplastic disorder. • Fibroblasts in the synovial stroma convert to a developmental program of chondrocytes instead of fibroblasts. • They are nourished by synovial fluid and stimulated to proliferate, giving rise to a tumor like mass attached to the synovium. • At the center of the chondroblastic mass, further metaplasia results in the formation of osteocytes, which form bone.

Epidemiology: • Most cases occur after 40 years of age. • Predominantly found in males.

General Gross Description: • Also referred to as synovial chondromatosis, synovial chondrometaplasia. • The most appropriate term seems to be the last, since this lesion seems to represent a metaplatic rather than neoplastic disease. • Chondrocytes appear at the tips of synovial villi. • Proliferation results in the formation of small masses. • Grossly, there are cartilagenous masses attached to the synovial membrane. • Subsequent detachment results in the formation free chondromatous bodies lying free in the joint space. • These are called joint mice.

General Microscopic Description: • Composed often of a core of normal bone, surrounded by cartilage. • Both the cartilage and bone are histologically benign.

Clinical Correlations: • Could affect range of movement of a joint. • Long term, can cause degenerative joint disease. • Can recur after resection. • Knee is the joint most commonly affected.

References: •E. Aegerter and J.A. Kirkpatrick, Jr. "Orthodpedic diseases" 4th Edition. W.B. Saunders. 1975. pp 682.