What is it about ?
A Baker’s cyst or popliteal cyst is a small lump that appears at the back of the knee (in the popliteal fossa).
In the popliteal fossa, there are several small pockets (bursa) that contain lubricating fluid (synovial fluid). These pockets can be connected with each other and with the knee joint. If fluid builds up abnormally in the knee, these bursae swell and can form a cyst.
In children, Baker’s cyst can be present from birth. In adults, it usually occurs as a result of a knee injury or disease, which causes fluid to build up in the knee (torn meniscus, ruptured ligament, inflammation (arthritis) or osteoarthritis).
What is its frequency?
Out of 1000 people who see a general practitioner, 14 have knee problems. Out of 100 knee problems, there are 3 Baker’s cysts. In reality, the numbers may be more important because people do not necessarily see a general practitioner for this type of problem.
How to recognize it?
The cyst usually does not cause symptoms. You just observe a soft, elastic, non-painful (painless) swelling in the back of the knee. In some cases, the cyst can grow to the size of a tennis ball. In this case, you feel it much more, it is painful and is accompanied by a feeling of stiffness, as it prevents you from fully bending the knee.
If this cyst is due to another disease, you often have other symptoms associated with that condition.
- With inflammation and fluid buildup, the knee may be red, hot, and swollen.
- Tears of the meniscus or ligaments are usually the result of a sports injury.
- With osteoarthritis of the knee, you suffer from stiffness, sometimes swelling, and you cannot stretch or bend the knee completely.
Exceptionally, the cyst can tear. You will then feel a strong pain and a swelling which extends to the calf.
How is the diagnosis made?
Your general practitioner usually makes the diagnosis on the basis of a simple examination of the knee. If in doubt, an ultrasound can be performed.
Sometimes the swelling of the calf (following the tearing of the cyst) is reminiscent of a disease of the veins in the leg (thrombosis). Ultrasound allows the correct diagnosis to be made.
If your doctor thinks of a tear in the meniscus or a ruptured ligament, an MRI may be done. If he thinks of osteoarthritis, he may order an x-ray.
What can you do ?
Most often you do not need to do anything, especially if you have no pain and the cyst is not bothering you. You can try to use your knee less for a little while. This can help clear the cyst. But you should know that this type of cyst can come back many times.
What can your doctor do?
If the cyst comes back several times (recurrent cyst) or the symptoms are bothersome, the doctor may aspirate the fluid through a needle. If this treatment does not provide relief, it is sometimes necessary to have the cyst removed by a surgeon. This is often the case after a sports accident.
If the cyst tears, there is no specific treatment.