A key step in the pathogenesis of rheumatoid arthritis is pannus formation. Within the joint space, pannus refers to hyperplastic, thickened synovium, which forms as a consequence of persistent synovial inflammation. It is a highly cellular tissue, containing macrophages and synoviocytes, among other components.

Rheumatoid arthritis (RA) symptoms include swollen joints that may feel spongy when the skin over them is pressed. This spongy feeling is caused by pannus, an abnormal tissue that develops because of excess inflammation. Pannus leads to painful arthritis symptoms as well as the destruction of joint cartilage and bone.

The pannus is an abnormal layer of tissue that can form in the joints of individuals with rheumatoid arthritis (RA). RA causes synovitis — inflammation of the protective tissue that lines joints (called the synovium) — and excess synovial fluid buildup. This excess synovial tissue can form the pannus, which can be damaging to the joint.

Pannus is an abnormal growth of tissue that develops in the joints. It can form in the later stages of rheumatoid arthritis. Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation in the joints. When a person has RA, the synovium, which is the protective lining of the joints, grows much thicker.