Baker's cysts are also known as popliteal cysts. The popliteal area is the area behind the knee. It is bordered by the hamstring muscles above and the calf muscles below. It is an important space because it contains the major artery, vein and nerves to your leg. Baker's cysts are simple cysts that form in this space. You may be able to feel the swelling in this area, or you may feel a fullness when you bend your knee or squat. They generally occur on the medial (towards the other knee) side of the popliteal space. They arise between the medial head of the gastrocnemius muscle and the semimembranosus muscle.
Dr. William Baker
These cysts were first described by the surgeon William Baker in the late 1800s. The name is a bit misleading, though, since the cysts have nothing to do with the profession of baking bread.
The cysts usually occur due to increased joint fluid production in the knee joint. Conditions such as arthritis or meniscus tears can irritate the joint, and the joint lining will produce more fluid to dilute the irritation or wash it out. This can result in an effusion (water on the knee), or the fluid can be pushed backwards into the popliteal space. Most times, there's still a link between the cyst and the joint. Occasionally, however, it can become pinched off or the connection can become like a one-way valve, trapping the fluid in the cyst. Things that increase joint fluid production usually make the baker's cyst grow bigger. Exercising, squatting, running and sports can increase the size of the cyst. Conversely, resting, icing and taking anti-inflammatory medications can decrease the size.
They Can Burst Spontaneously
Though this doesn't usually happen, the cyst may rupture spontaneously or due to some trauma. The calf can swell and become red and inflamed, and there may be bruising clear down to the heel. Of course, these are also warning signs of a possible blood clot (deep venous thrombosis, DVT), so you should seek medical attention if this happens.
If the cyst doesn't go away with resting and activity modification, consider a cortisone injection. The doctor can withdraw (aspirate) fluid out of the cyst and inject a corticosteroid to reduce inflammation. If the injection doesn't help, surgery is the next option. Before undergoing surgery, obtain an MRI to assess your joint for any underlying causes, most commonly a meniscus tear. The MRI will also confirm the presence of the cyst. In some instances, a patient may notice swelling behind the knee, but the MRI will not show any fluid collection there. Once the diagnosis is confirmed, talk to your orthopedic surgeon about your options.