Your body has strategically-placed, fluid-filled cushions called “bursa” around each joint. Bursa act to reduce friction where muscular tendons rub on bone. Your knee is surrounded by several bursa that share fluid with the inside of your knee joint and with each other. You can think of this like a chain of lakes connected by streams. If the inside of your knee joint or any of the bursa around your knee becomes inflamed, the entire system fills. When swelling exceeds each individual bursa’s capacity, this fluid creates a soft balloon-like swelling of the popliteal bursa behind your knee called a “Popliteal cyst”, or more commonly a “Baker’s cyst”.
This swelling is usually not from a problem with the popliteal bursa itself, but rather, inflammation somewhere else in the joint that has distended the popliteal bursa. This swelling is often the result of arthritis or damage to a ligament or cartilage within the knee.
A Baker’s cyst is often painful, and the discomfort may increase when you attempt to move your knee. Depending on the severity of your swelling, your symptoms may vary between a feeling of fullness and significant pain. It is not unusual for a Baker’s cyst to change in size from day to day, depending on the amount of swelling. Be sure to tell us if your pain progressively increases when you walk or if you notice warmth, redness or swelling in your calf, as these could be signs of a more significant problem.
Sometimes rest and elevation of your leg help to alleviate pain and swelling. Initially, you may need to avoid activities, like squatting, kneeling, heavy lifting, climbing stairs, or running. Wearing a brace on your knee may compress the cyst and cause an increase in your pain. Since Baker’s cysts are generally a problem that is secondary to another condition, treatment is most effective when directed at the underlying problem.