A BAKERS CYST is a swelling in the back of the knee. It is also called a POPLITEAL CYST because the proper name for the soft area at the back of the knee is the popliteal fossa. A Bakers cyst can be very small, and only detectable with a scan, or very large and apparent as a firm lump up to several centimetres across. It is not dangerous but can be uncomfortable. The cause of a bakers cyst is an out-pouching of the normal knee lining becoming filled with fluid. The fluid is just an excessive amount of the normal fluid which lubricates the knee joint, called synovial fluid.
If in doubt, the diagnosis can be confirmed with an MRI or ultrasound scan.
There is no direct treatment of the cyst. Taking the fluid off with a needle usually results in recurrence of the cyst and can be dangerous.
Surgical removal of the cyst is potentially dangerous to nerves and blood vessels, has a high risk of recurrence and is unnecessary. Sometimes they disappear spontaneously, or burst causing pain in the calf which can be inflamed for a few days. This is not dangerous but is sometimes mistaken for a DVT (blood clot). Surgery to treat the cause of excess fluid, for example to treat a cartilage tear or arthritis, often gets rid of the bakers cyst.