The inner layer of the joint capsule, called the synovial membrane, is composed of areolar connective tissue containing elastic fibers. The synovial membrane lines the inside of a mobile joint, specifically the inside of the fibrous capsule. In many synovial joints, the synovial membrane accumulates fatty tissue called adipose bodies. The infrapatellar fat body of the knee is an example. The cells of the synovial membrane, the synoviocytes, are not frequently visualized in the synovial fluid or synovium, but they play an essential role in the function of the hemosynovial barrier. They are the first to phagocytose the crystals and trigger the inflammatory process. The synovial membrane may be inflamed in arthritis. In general, the inflammation of the synovial membrane is called synovitis. This can be caused by an intra-articular infection (septic arthritis), lupus erythematosus, inflammatory arthritis (such as rheumatoid arthritis), gout.