Most cases occur after 40 years of age. Predominantly found in males. Also referred to as synovial chondromatosis and 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 of free chondromatous bodies lying free in the joint space. These are called joint mice. Composed often of a core of normal bone, surrounded by cartilage. Both the cartilage and bone are histologically benign.