Osteochondromatosis, also known as synovial chondromatosis or synovial osteochondromatosis, is common in the knee joint. The free bodies may be single or multiple and may number up to several thousand. The early lesion is a villous hyperplasia of the synovium, which gradually increases in size to form osteochondral vesicles, which are attached to the synovium and grow through the tip, or for some reason the tip breaks off and forms a free body. The free body loses its blood supply and the cartilaginous part of the bone dies on its own, absorbing nutrients from the synovial fluid. The main clinical manifestations of the disease are joint pain, swelling, weakness, and progressive movement disorders. Sometimes there is interlocking and severe pain, which can be unlocked automatically with rest or limb braking. In some patients, easily movable free body is felt in the suprapatellar capsule, and there is a ringing sound on examination and quadriceps atrophy. x-ray examination: early or free body without calcification is not well developed. Arthrography helps in the diagnosis; multiple small circular shadows are seen after calcification of the free body. Arthroscopy can confirm the diagnosis. Surgery is the only method of treatment for this disease. The free body is removed as much as possible, and the synovial membrane with lesions is also removed, preserving the healthy part and minimizing the joint movement. In severe cases, arthroplasty or joint fixation is feasible.