Popliteal cyst

A Baker's cyst, also known as a popliteal cyst, is a fluid-filled sac in the back of the knee. It often occurs in chronic knee joint diseases, such as osteoarthritis or rheumatism, but also in chronic meniscal damage.

The damage to the knee joint causes irritation of the synovial membrane. This then produces increased amounts of synovial fluid. This leads to a permanently elevated intra-articular pressure. To relieve the pressure in the joint, the fluid seeks an outlet. Since the kneecap is located at the front of the knee and the taut ligaments are located on the sides, the synovial fluid presses backward into the soft back of the knee. Relaxation of the surrounding connective tissue then leads to the formation of a fluid-filled sac, also known as a cyst. Baker's cysts can occur at any age, but most commonly affect middle-aged to older people.

How does the patient notice the cyst?

The main symptoms of a Baker's cyst are pain and movement-dependent, frequently recurring swelling in the back of the knee. The pain occurs primarily when kneeling or sharply bending the joint. If the cyst ruptures, sudden, shooting pain occurs in the back of the knee.

How does the doctor diagnose Baker’s cyst?

A Baker's cyst is diagnosed based on symptoms and examination findings. Pain can often be caused by pressure on the back of the knee.
Ultrasound examination (sonography) has become established to confirm the diagnosis of a Baker's cyst. Ultrasound can precisely determine the location of the cyst, its fluid content, and its size. Using our modern ultrasound equipment, we can also perform a Doppler scan. This ultrasound technique can visualize blood flow in the vessels. This also allows us to rule out any existing drainage obstructions caused by cyst pressure. This is even an advantage over conventional magnetic resonance imaging.
A normal X-ray can reveal arthritic changes in the knee joint or, in very rare cases, bone tumors as the cause of the symptoms.

Treatment of Baker's cyst

In general, conservative and surgical treatment options are available for Baker's cysts. The goal of treatment is to permanently relieve the discomfort, swelling, and pain in the back of the knee. It is always important to first determine the possible cause of the Baker's cyst. The irritation in the joint should be reduced so that synovial fluid production returns to normal. Treatment must then be planned based on the cause of the impaired synovial fluid production. In cases of rheumatism or osteoarthritis, medication can be used to reduce the irritation in the joint.

If the cyst is under significant pressure, it can also be punctured, meaning the fluid is drained with a needle. Using our modern ultrasound technology, this is possible with minimal risk. Even if the cyst is located close to major blood vessels, it can be reliably identified. The path of the needle can also be visualized on the ultrasound, ensuring that the needle tip is always positioned exactly in the center of the cyst during puncture.

If an internal knee injury, such as a meniscus tear, is the cause of the cyst, surgical treatment is preferable to conservative therapy.

In cases of very large cysts and unsuccessful treatment, the cyst itself can be removed. In Baker's cysts connected to the joint capsule, care must be taken to occlude the duct connecting the cyst to the knee joint. However, even with this procedure, it must be kept in mind that if the underlying cause of the cyst remains untreated, there is a high probability that a new cyst will form.