What is a baker's cyst?

See below: It is a benign swelling of the popliteal bursa located behind the knee!

Swelling: Cystic swelling behind knee, causing deformity pain, joint dysfunction. Slow but progressive. May be associated with rheumatoid arthritis.

Knee cyst: It is a fluid filled sack in the crease behind your knee. The cyst can be associated with a torn meniscus cartilage inside the knee, which allows the knee synovial fluid to escape and form the cyst.