Baker’s Cyst (Popliteal Cyst)

A baker’s cyst is a small (sometimes large) sack of fluid behind the knee. The sack itself is quite normal. Most people have one but it usually does not have enough fluid in it to be noticeable. It will cause problems only when it becomes swollen with fluid, especially if the communication with the knee joint is via a one-way valve which lets fluid out into the cyst but prevents fluid from flowing back into the knee.

The cyst can vary in size from quite small causing a feeling of fullness in the back of the knee to very large with a definite lump.The fluid is often due to some problem within the joint itself such as arthritis or a torn cartilage. Occasionally the cyst fills up with fluid for other reasons. It can still occur even after knee replacement surgery.

Occasionally the cyst can leak fluid into the calf and cause calf swelling and pain. This may simulate a calf DVT (deep vein thrombosis). It can be diagnosed by a careful examination and occasionally an ultrasound scan or MRI scan may be indicated. Generally no treatment is required. Bakers cysts often fluctuate and may eventually fade away. If the cyst is small and not causing much trouble it is generaly advised to leave it alone.

If the cyst is large then draining the fluid will relieve the swelling although the cyst will often recur. If the cyst is large and very symptomatic and the cause of the excess fluid is due to a cartilage tear or arthritis then this may need to be addressed surgically. A large and persistent Bakers cyst may require open surgical removal which is done through an incision across the back of the knee although this is rare

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