A Baker's cyst is a common cyst in the back of the knee and is usually caused by an increased buildup of synovial fluid in the knee joint. A Baker's cyst often appears as a swelling in the back of the knee and can cause various symptoms. A Baker’s cyst is often caused by an underlying condition such as osteoarthritis, rheumatoid arthritis, or inflammation.
The increased production of synovial fluid leads to a bulge in the joint capsule. A Baker’s cyst may remain asymptomatic for a long time, but it can also cause severe pain and limited mobility. Ultrasound, MRI, and other imaging techniques are used for diagnosis. Treatment depends on the cause of the Baker’s cyst and the specific symptoms present. Early treatment can help alleviate symptoms and prevent complications.
Definition and Causes of a Baker's Cyst
A cyst is a cavity filled with synovial fluid. When synovial fluid from the knee joint accumulates in the back of the knee, it is referred to as a Baker’s cyst. This accumulation of fluid causes a bulge in the back of the knee. The Baker’s cyst was originally also known as a popliteal cyst (popliteal = relating to the back of the knee).
The cause of a Baker’s cyst is usually inflammation or severe irritation of the knee joint. As a result, the body produces more synovial fluid, which accumulates under the skin in the back of the knee.
The fluid cannot drain because the muscles surrounding the joint compress the tissue. This creates a natural valve: new fluid continues to accumulate in the Baker’s cyst, while drainage is not possible.
Symptoms of a Baker’s cyst
A Baker’s cyst causes a feeling of tightness in the back of the knee, especially when the joint is extended. Due to the accumulation of fluid, those affected are often unable to fully bend the knee. Pain may also occur.
If the cyst becomes severely enlarged, it can press on nerves and blood vessels. If the veins are compressed, venous outflow disorders may occur. These resemble the symptoms of a lower leg venous thrombosis.
Under certain circumstances, the cyst may rupture. This can cause severe pain. As a result, signs of inflammation often appear in the knee and lower leg, manifesting as redness and swelling.
Diagnosis of a Baker’s cyst
Larger Baker’s cysts can usually be easily felt in the back of the knee. Imaging tests clearly show a Baker’s cyst. An ultrasound examination is often used for this purpose, and sometimes magnetic resonance imaging (MRI) is also employed.
Diagnosing a Baker’s cyst also involves identifying the underlying condition, such as
- meniscal tear,
- knee osteoarthritis,
- ligament instability, or
- a rheumatic disease.
The underlying condition causing a Baker’s cyst must also be identified.
On the left, a healthy knee joint; on the right, a knee joint with a Baker’s cyst in the popliteal fossa © designua | AdobeStock
Treatment of a Baker’s cyst
Treatment for a Baker’s cyst depends on its severity. Small Baker’s cysts can be treated with medication. For larger fluid accumulations, the cyst can be punctured and the fluid removed. To prevent another Baker’s cyst from forming, the underlying condition must be treated. Surgical removal of a Baker’s cyst is justified only in exceptional cases.
Baker’s Cyst Specialists – Education and Training
Orthopedic surgeons treat all conditions of the musculoskeletal system. This includes Baker’s cysts. After completing medical school, an orthopedic surgeon undergoes further training to become a specialist in orthopedics and trauma surgery. The residency period in trauma surgery/orthopedics is 72 months.
FAQ
What is a Baker’s cyst?
A Baker’s cyst is a cyst filled with synovial fluid located in the back of the knee. It develops as a protrusion of the joint capsule in the back of the knee and is usually connected to the knee joint. A Baker’s cyst often occurs in cases of chronic joint disease or following an injury to the knee.
How does a Baker’s cyst develop?
A Baker’s cyst develops when excess synovial fluid is produced in the knee joint. The excess synovial fluid accumulates in a protrusion of the joint capsule, leading to the formation of the cyst. Common causes include osteoarthritis, rheumatoid arthritis, inflammation, or other joint disorders. The underlying cause of a Baker’s cyst should always be treated.
What symptoms does a Baker’s cyst cause?
Symptoms of a Baker’s cyst include swelling behind the knee, a feeling of pressure, pain, and limited mobility. Symptoms may occur especially during physical activity or when the leg is straightened. Larger Baker’s cysts can affect surrounding tissues, blood vessels, or the calf.
How is a Baker’s cyst diagnosed and treated?
If a Baker’s cyst is diagnosed, it is usually evaluated using ultrasound and MRI. Treatment for a Baker’s cyst depends on the underlying condition. Physical therapy, anti-inflammatory measures, and treatment for osteoarthritis or rheumatoid arthritis can help alleviate symptoms. In certain cases, aspiration or surgical treatment may be necessary.
What happens if a Baker’s cyst ruptures?
If a Baker’s cyst ruptures, the leaked fluid can enter the calf and cause sudden, severe pain. The symptoms sometimes resemble those of a blood clot. Therefore, if you experience acute pain in the back of the knee or calf, you should seek medical evaluation.
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About the medical author
Prof. Dr. med. Wolfgang Rüther
Prof. Dr. med. Wolfgang Ruether – author: Explore expert medical articles in the Leading Medicine Guide.
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