The synovial membrane is a thin layer of tissue that lines the part of a joint that acts as a shock absorber between joints of bones. When the synovium thickens and fragments break off, the pieces may grow, calcify (become bone-like nodules) and become loose in the joint. This is synovial chondromatosis. Usually this process is benign (non-cancerous), however rarely, SOC may be become malignant. Learn more about Synovial Chondromatosis.