Rheumatoid arthritis: is a chronic systemic autoimmune disease characterized by synovitis of the joints. The persistent and recurrent attacks of synovitis can lead to destruction of cartilage and bone in the joints, joint dysfunction, and even disability. The disease is also known as rheumatoid disease because the vasculitis lesions involve various organs throughout the body. Local manifestations of the disease include inflammation of the synovial membrane of the joint cavity, ooze, cell proliferation, granuloma formation, destruction of cartilage and bone tissue, and finally joint ankylosis and dysfunction. The disease mostly affects small joints, such as the hand, foot and wrist joints, and is often symmetrical and chronic, with temporary remission. The pathological changes in the joints of rheumatoid arthritis: The tissue changes of rheumatoid arthritis may vary slightly depending on the location, but the basic changes are the same. They are characterized by: (1) lymphatic or plasma cell infiltration in diffuse or restricted tissues, or even lymphoid follicle formation. (ii) Vasculitis, accompanied by endothelial hyperplasia narrowing and obstruction of the lumen, or fibrin-like necrosis of the lumen wall. (iii) rheumatoid granuloma formation. Changes in the joints: for synovitis, the synovial membrane is congested, edematous and infiltrated by a large number of monocytes, plasma cells, lymphocytes, sometimes with lymphoid follicle formation, often with vesicles formed by superficial synovial cell necrosis in the cell, and covered with fibrin-like deposits. The latter consists of a complement complex containing a small amount of gamma globulin, with an accumulation of exudate containing neutrophils in the joint cavity. Further changes in synovitis are the formation of vascular opacities in which, in addition to proliferating fibroblasts and capillaries that thicken the membranous villi, there is lymphoid follicle formation, infiltration of plasma cells and granulocytes and varying degrees of vasculitis, and proliferation of synovial cells. These proliferating synovial cells, or lymphocytes and plasma cells, contain fluorescein-binding antigens that can be used to detect rheumatoid factor, gamma globulin, or antigen-antibody complexes. The vascular opacities can gradually extend from the synovial membrane at the edge of the articular cartilage to the cartilage surface, where they are covered, blocking the contact between cartilage and synovial fluid and affecting its nutrition. In addition, due to the erosive effect of certain hydrolytic enzymes released from the vascular opacities on the collagen matrix in the articular cartilage, subchondral bone, ligaments and tendons, the joint cavity is destroyed, the upper and lower articular surfaces fuse, fibrotic stiffness, dislocation, and even ossification, joint fusion, and complete loss of function, and the adjacent bone tissue becomes disused and sparse.