Synovium of the Knee Joint
Assistant
Definition
By Gregory R. Waryasz, MD
The synovium of the knee joint of the musculoskeletal system is characterized by being a vascularized connective tissue that lacks a basement membrane.
It is part of the hip joint. It consists of two cell types. Type A cells are important for phagocytosis of foreign bodies. Type B cells produce synovial fluid.
Its unique structural feature is that it lines the inside of the joint capsule. The synovial cavity has many compartments within the knee joint.
The synovium as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.
The function of the synovium is to produce synovial fluid. Synovial fluid is important for reducing friction with movement. Synovial fluid is a glycoprotein. The synovium also mediates nutrient exchange between blood and synovial fluid.
Common diseases include rheumatoid arthritis, systemic lupus erythematosus (SLE), synovial chondromatosis, plica synovialis, and pigmented villonodular synovitis (PVNS).
Rheumatoid arthritis is an autoimmune condition where the body mounts an immune response against the synovial tissue as well as other organs. This leads to synovitis and joint destruction.
Systemic lupus erythematosus is an autoimmune condition where the body mounts an immune response against the body’s own cells and tissue. SLE can cause synovitis.
Synovial chondromatosis is a condition of the synovium where there is a metaplastic conversion of cartilage tissue into ossified/bony loose bodies.
Plica synovialis refers to embryological invaginations that persist into adulthood leading to pain particularly in the anterior knee.
Pigmented villonodular synovitis (PVNS) is a condition of a slow growing and benign tumor of the synovium. It is a cause of bone erosion and tissue damage in addition to joint swelling and pain.
Commonly used diagnostic procedures include clinical history, physical exam, and MRI.
It is usually treated with physical therapy and anti-inflammatory medications. Surgery can be performed either with a large open incision or performed with arthroscopy to remove tissue of PVNS, synovial chondromatosis, and arthritis. Joint replacement may be necessary for joint destruction.
References
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.