Baker’s cysts (popliteal cysts)

An overview of Baker’s cysts

A Baker's cyst, also known medically as a popliteal cyst, is a swelling filled with joint fluid in the joint capsule of the hollow of the knee. It occurs when excess fluid leaks into a bursa in the hollow of the knee and a cyst forms. The bulge in the affected joint is usually soft and elastic and may increase in size when the knee is moved. In some cases, it becomes so large that it can be clearly seen or felt.

Causes

A Baker's cyst usually indicates an underlying disease or damage to the knee joint and occurs predominantly in middle and old age. Potential triggers include:

• Meniscus damage
• Cruciate ligament rupture
• Knee osteoarthritis
• Rheumatic diseases

The injuries or underlying diseases listed lead to the formation of excessive fluid in the knee. This increases the pressure in the knee joint and can lead to the joint capsule protruding into the hollow of the knee.

Disease progression

The disease progression of a Baker's cyst varies depending on the size of the cyst and its underlying cause. In the majority of patients, the Baker's cyst forms slowly over a long period of time and usually causes mild to moderate symptoms such as swelling, pain or a feeling of tension in the hollow of the knee. The symptoms may vary over time and may either increase or decrease. The cyst, however, can also suddenly become larger or inflamed, and in rare cases even burst, leading to severe pain and swelling in the knee.

Symptoms 

The symptoms of a Baker's cyst can vary depending on the size of the cyst. Smaller cysts often cause little or no discomfort to the affected joint and may go unnoticed. Larger ones, however, can be externally visible and palpable. They can be associated with a feeling of tension, pain and stiffness in the knee or calf.

Bulges or pain in the hollow of the knee should always be checked by an orthopaedic specialist because in addition to a benign cyst, they may also indicate other serious diseases such as venous thrombosis or a malignant tumour in the knee area.

Diagnosis

A Baker's cyst can often be diagnosed on the basis of the characteristic bulge in the hollow of the knee and the associated symptoms. In order to obtain a more precise assessment of the size and location of the cyst, an ultrasound examination is usually performed. Because the Baker's cyst is often the result of damage to the knee joint or chronic inflammation, a thorough examination of the entire knee is also performed. X-ray images or MRI examinations may also be used within this process.

Treatment 

As with the disease progression and the symptoms, the treatment of a Baker's cyst also depends on the size of the cyst and the extent of the patient's symptoms.

Small to medium-sized Baker's cysts without severe symptoms

Often in the case of small Baker's cysts, the change in the affected knee is observed and the symptoms are alleviated with conservative therapy.