Baker’s cyst describes a condition where the knee produces too much of the fluid that helps your leg swing smoothly and without friction between the moving parts. A cyst becomes filled with this synovial liquid and causes a bulge on the knee and a feeling of tightness behind your knee that gets worse when you try to flex or extend the knee. Baker’s cyst is often a result of another underlying problem with the knee joint, such as arthritis or a cartilage tear.

Baker’s cysts may become complicated when the fluid starts leaking into the calf, causing even more pain in the knee, swelling in the calf, redness in the calf and a feeling that water is moving down the leg.

Because these symptoms can resemble those of other serious conditions such as a blood clot, your doctor will test with an ultrasound or an MRI to determine the specific cause of your symptoms. Medication, physical therapy and fluid drainage are the typical treatment for Baker’s cyst.

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