Baker's cyst, a collection of synovial fluid which has
escaped from the knee joint or a bursa and formed a new synovial-lined
sac in the popliteal space; seen in degenerative or other joint
Not generaly seen on a plain radiograph unless extensive, demonstrated on, a modified arthrogram, ultrasound, ct and MRI
A bakerís 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 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.
Occasionally the cyst can leak fluid into the calf and cause calf
sweeling, tightness & pain. This may even simulate a calf DVT (deep
It is easily diagnosed by a careful examination and an ultrasound
Sometimes the cyst communication can be seen arthroscopically and
the one-way flap valve excised.
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. 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.
Image 1 Diagram of a Bakers
Image 2 MRI of a Bakers
Image 3 Arthrogram of a Bakers Cyst