A baker’s cyst, or popliteal cyst, is a collection of fluid behind the knee. It is benign, and often asymptomatic. If it gets severe enough, it can cause pressure on the local nerves and vasculature which will provoke pain and stiffness in the knee. It will usually be difficult to fully flex the knee. 

There is a bursa behind the knee, namely the gastrocnemio-semimembranosus bursa. On the medial side there is a one way valve from the knee into the bursa. When there is any type of inflammatory process in the knee and the swelling builds faster than it can be evacuated, it accrues and pushes into the bursa. Because of this, baker’s cysts are associated with degenerative processes of the knee such as cartilage damage, meniscus tears, or rheumatoid arthritis. 

Sometimes the cyst can rupture which will initially cause some pain and swelling in the calf. It is important to note that a DVT (clot) be ruled out because this can be life threatening. A ruptured cyst can mimic the symptoms of a DVT. 

The bursa can be aspirated (drained) however, if the underlying issue is not addressed, it will just come back. This is not to say that surgery is necessary. The knee is about position and quality of movement. It is thought of as a hinge joint that just bends and straightens, but there is an element of rotation to the knee as well. If the knee is rotated internally (knee caved in) or externally (knee bowed out) it can change the relationship of the femur and tibia. If there is some defect such as a meniscus tear, this rotation can expose it and irritate it further provoking swelling. 

Where does this rotation come from? More often than not, the ankle. Stand barefoot, and slowly roll your ankle in and out. Watch what it does to your knee. If you are flat footed, it will lead to an internally rotated position of the knee and often cause pain when squatting. To fix this, you have to restore your arch and range of motion in dorsiflexion. Here is my favorite exercise for dorsiflexion:

And here is a way to train your arch with squatting:

A general principle in rehab is that there are symptoms and dysfunctions. The dysfunction causes the symptom. You just have to look at the adjacent joint to find the dysfunction, as this is a prime example. Missing range of motion in the ankle changes how you squat, which provokes swelling and pain. Resolve the range of motion and work on technique, and you just might keep it from coming back.

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