A Baker’s cyst is a sack-shaped dilation filled with joint fluid that is found in the knee joint capsule in the popliteal space (back of the knee). It is caused by an increased production of joint fluid resulting from either a damaged meniscus or osteoarthritis in the knee joint. Palpable swelling and a feeling of tightness or pain at the back of the knee are classic symptoms of a Baker’s cyst.
A Baker’s cyst always indicates damage in the knee joint. Patients presenting with a Baker’s cyst are frequently diagnosed with knee joint osteoarthritis, a damaged meniscus or a rheumatic disease. These diseases all result in increased fluid production in the knee joint, which increases the pressure inside the joint capsule. This in turn can cause the joint capsule to protrude into the popliteal space at the back of the knee. The first person to identify this protrusion was W.M. Baker, which is why it is called the Baker’s cyst. Baker’s cysts primarily affect middle aged and elderly people.
The symptoms vary depending on the severity of the Baker’s cyst. Smaller cysts cause few or no symptoms. Larger cysts can be seen and felt on the surface of the skin. They are often associated with a feeling of tightness and pain at the back of the knee or in the calf. Swelling or pain in the popliteal space should always be checked out by a doctor. Such symptoms could also indicate venous thrombosis or in rare cases even a malignant tumour.
A Baker’s cyst can often be diagnosed simply on the basis of the typical swelling at the back of the knee and the associated pain and discomfort. An ultrasound examination is used to determine the size and exact location of the cyst. Given that the cyst is usually the result of a damaged knee joint, the joint is also extensively examined. This involves x-ray imaging or an MRI examination.
The treatment of a Baker’s cyst depends on the size of the cyst and the level of pain and discomfort. Large cysts can be lanced to reduce the pressure in the knee. Generally, an attempt is made to treat the Baker’s cyst conservatively using pain killers and anti-inflammatory medication. However, if conservative treatment does not result in any improvement over a long period of time, or if the Baker’s cyst comes back, it is advisable to have it surgically removed.
If the Baker’s cyst is caused by a meniscus injury, then the damaged meniscus needs to be treated accordingly. Find out more about this in the knee joint imaging section. In cases of advanced knee joint osteoarthritis, a joint replacement is sometimes unavoidable. Find out more about this in the knee prosthesis section.