Bakers 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 comminication 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 almost always 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. Sometimes it occurs after Knee Replacement surgery.
Occasionally the cyst can leak fluid into the calf and cause calf sweeling, tightness & pain. This may even simulate a calf DVT (deep vein thrombosis)
It is easily diagnosed by a careful examination and an ultrasound scan.
It is best treated by treating the cause of the excess fluid (fixing the cartilage tear or arthritis) and then the Bakers cyst usually fades away, but occasionally surgery is needed. If the cyst is small and not causing much trouble, leaving it alone is safe. Draining the fluid will relieve the swelling but the cyst will usually quickly come back as the primary problem has not been treated.
Sometimes the cyst communication can be seen arthroscopically and the one-way flap valve excised.
A large and persistent Bakers cyst may require surgical removal which is done through an incision across the back of the knee, although it can sometimes be removed by arthroscopic surgery direct to the cyst.