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Causes
By Mayo Clinic staff
The cartilage and tendons in your knee rely on a lubricating fluid called synovial (si-NO-vee-ul) fluid. This fluid helps your leg swing smoothly and reduces friction between the moving parts of your knee.
Synovial fluid circulates throughout your knee and passes in and out of various tissue pouches (bursae) throughout your knee. A valve-like system exists between your knee joint and the bursa on the back of your knee (popliteal bursa). This regulates the amount of synovial fluid going in and out of the bursa.
But sometimes the knee produces too much synovial fluid, resulting in buildup of fluid in the bursa and what is called a Baker's cyst. This can be caused by:
- Inflammation of the knee joint, such as occurs with various types of arthritis
- Knee injury, such as a cartilage tear
- Foley BA, et al. Injection therapy of bursitis and tendinitis. In: Roberts JR, et al. Clinical Procedures in Emergency Medicine. 5th ed. Maryland Heights, Mo.: Saunders Elsevier; 2009. http://www.mdconsult.com/das/book/body/184552931-3/955852100/2083/443.html#4-u1.0-B978-1-4160-3623-4..00052-3--s0245_2527. Accessed Feb. 19, 2010.
- Rupp S, et al. Popliteal cysts in adults. American Journal of Sports Medicine. 2002;30:112.
- Handy JR. Popliteal cysts in adults: A review. Seminars in Arthritis and Rheumatism. 2001;31:108.
- Cleveland KB. Nontraumatic soft-tissue disorders. In: Canale ST, et al. Campbell's Operative Orthopaedics. 11th ed. Philadelphia, Pa.: Mosby Elsevier; 2007. http://www.mdconsult.com/das/book/body/184837580-2/0/1584/169.html?tocnode=55686842&fromURL=169.html#4-u1.0-B978-0-323-03329-9..50027-1--cesec17_905. Accessed Feb. 19, 2010.
- Centeno CJ, et al. Sclerotherapy of Baker's cyst with imaging confirmation of resolution. Pain Physician. 2008;11:257.
- Laskowski ER (expert opinion). Mayo Clinic, Rochester, Minn. Feb. 24, 2010.
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