A Baker's cyst is a fluid-filled cyst that causes a bulge and a feeling of tightness behind your knee. The pain can get worse when you fully flex or extend your knee or when you're active.
Image courtesy - Mayo Foundation
A Baker's cyst is usually the result of a problem with your knee joint, such as arthritis or a cartilage tear. Both conditions can cause your knee to produce too much fluid, which can lead to a Baker's cyst.
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It is very important to know that the Bakers Cyst is an effect of an underlying Condition. It is not the primary problem. So getting the cyst drained or removed without treating the underlying condition will just cause the Cyst to reappear.
Although a Baker's cyst may cause swelling and make you uncomfortable, treating the probable underlying problem usually provides relief.