The Function of Synovium in a Joint

The synovium, also called the synovial membrane, is the soft tissue that lines the spaces of diarthrodial joints, tendon sheaths, and bursae. The synovium lines the entire inner surface of the joint, except where the joint is lined with cartilage. The synovium has an outer layer (subintima) and an inner layer (intima). The cells of the intima are called synoviocytes. There are two types of synoviocytes, type A (macrophage-derived) and type B (fibroblast-derived). The subintima consists of intra-articular (within the joint) vessels, such as blood vessels and lymphatic vessels, and nerves. Underneath the layer of synoviocytes, there is either adipose tissue or fibrous tissue. The synovium is where synovial fluid is produced, the substance that lubricates and nourishes the cartilage and bones inside the joint capsule.

X-ray of knee - osteoarthritis and rheumatoid arthritis
Peter Dazeley / Getty Images

The Synovium in Rheumatoid Arthritis

Like many other rheumatic diseases, rheumatoid arthritis is an autoimmune disease. In an autoimmune disease or condition, a person's immune system, which normally helps protect the body from infection and disease, attacks their own joint tissues for unknown reasons. In rheumatoid arthritis, immune system cells travel to the synovium and initiate inflammation (synovitis). The inflammatory process is characterized by the proliferation of synovial cells, increased vascularization, and the infiltration of tissue by inflammatory cells, including lymphocytes, plasma cells, and activated macrophages. This manifests itself as typical symptoms of rheumatoid arthritis—warmth, redness, swelling, and pain.

As rheumatoid arthritis progresses, the inflamed synovium invades and destroys the cartilage and bone of the joint. The surrounding muscles, ligaments, and tendons that support and stabilize the joint become weak and unable to work normally. These effects lead to the joint pain and joint damage typically seen in people with rheumatoid arthritis. Understanding what happens to synovium in rheumatoid arthritis helps you to understand symptoms and disease severity.

Treatments to Target Inflamed Synovium - Are They Coming?

Researchers have been interested in developing tissue-specific treatments for rheumatoid arthritis. Potential drugs could target the synovium with increased efficacy and decreased systemic toxicity. If research into this process succeeds, imaging agents could be delivered directly to the synovium, allowing for an assessment of active synovitis in multiple joints. Although advancements have been made in this area, a specific synovial receptor has yet to be discovered.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Redondo ML, Christian DR, Yanke AB. The role of synovium and synovial fluid in joint hemostasis. In: Yanke A, Cole B, eds. Joint Preservation of the Knee. Cham, Switzerland: Springer; 2019: 57-67.

  2. Yap HY, Tee SZ, Wong MM, Chow SK, Peh SC, Teow SY. Pathogenic role of Immune cells in rheumatoid arthritis: implications in clinical treatment and biomarker development. Cells. 2018;7(10). doi:10.3390/cells7100161

  3. Ostrowska M, Maśliński W, Prochorec-Sobieszek M, Nieciecki M, Sudoł-Szopińska I. Cartilage and bone damage in rheumatoid arthritis. Reumatologia. 2018;56(2):111-120.

  4. Ouboussad L, Burska AN, Melville A, Buch MH. Synovial tissue heterogeneity in rheumatoid arthritis and changes with biologic and targeted synthetic therapies to inform stratified therapy. Front Med (Lausanne). 2019;6:45. doi:10.2174/1874312901105010115

Additional Reading