The connections formed between our bones with the help of fibrous tissue, cartilage, and bone are called joints or osseous joints. The most common bone connection is the synovial joint, which is basically composed of a joint capsule, a joint cavity and a joint surface. The joint capsule is a connective tissue that firmly connects two bones. The joint cavity is a narrow gap with a thin layer of lubricating fluid, like the lubricant in a machine, that reduces friction between bones to ensure flexible joint movement. Each joint has two or more bone surfaces in contact, called articular surfaces, one of which is slightly convex or spherical, called the joint head; the other is slightly concave, called the joint socket. The articular surfaces are lined with a layer of articular cartilage that reduces shock and friction. In the early stages of rheumatoid arthritis, the synovial membrane becomes inflamed and edematous with a large infiltration of inflammatory cells and covered with fibrin deposits. At the same time, the immunoreactive cells in the opacity release a variety of inflammatory mediators, protein hydrolases, collagenases, etc., which erode the articular cartilage, subchondral bone, ligaments and tendons. This results in bone resorption and destruction, muscle atrophy, ligament elongation and rupture, and finally joint deformity and restricted movement.