Arthritic joint debris. Cartilage and bone fragments removed from a joint of a patient with rheumatoid arthritis. Rheumatoid arthritis is caused by the immune system attacking the body's own tissues, causing progressive joint and cartilage destruction The degeneration of the joint triggers synovial chondromatosis, the formation of fragments of cartilage and bone in the fluid-filled space of the joint. The build-up of fragments causes stiffness and pain. Treatment is with the surgical removal of the fragments.