Baker’s Cyst

A Baker’s cyst is a fluid-filled sac that causes swelling, fullness, and a feeling of tightness behind your knee. The pain may worsen when you fully bend or extend your knee, or during physical activity.

Baker’s cyst usually develops after issues such as knee osteoarthritis or cartilage wear. These conditions can lead to the overproduction of joint fluid, which accumulates behind the knee and forms a cyst.

It is one of the most common causes of pain behind the knee. In many cases, when the underlying condition is treated, the Baker’s cyst also disappears.

What Is a Baker’s Cyst?

A Baker’s cyst is a fluid-filled sac located at the back of the knee joint. It typically forms when excess joint fluid pushes out into the popliteal space. The cyst is usually soft, movable, and painless — but as it grows, it may restrict movement and cause a feeling of tightness.

A Baker’s cyst is not a disease on its own; it is usually a sign of an underlying knee problem. Meniscus tears, osteoarthritis, rheumatoid arthritis, or trauma can increase joint fluid production, leading to cyst formation. It becomes more noticeable during activities such as squatting or climbing stairs.

According to scientific studies, Baker’s cysts are seen in 10–40% of patients with intra-articular knee conditions. A 2020 study published in Clinical Rheumatology found that 45% of patients with rheumatoid arthritis had Baker’s cysts detectable by ultrasound.

The study also suggested that these cysts may indicate synovial inflammation — a crucial clue for diagnosis and treatment planning.

Symptoms of a Baker’s Cyst

• Pain behind the knee (most common symptom)

• Swelling behind the knee and sometimes in the calf

• Stiffness and difficulty fully bending the knee

• Swelling and discomfort after walking, running, cycling, or prolonged standing

Note: Some people with a Baker’s cyst may have no pain at all.

What Causes a Baker’s Cyst?

Your knee contains a lubricating fluid called synovial fluid, which reduces friction between the moving parts of the joint. Sometimes the knee produces too much of this fluid, which accumulates in the popliteal bursa (the area behind the knee), resulting in a Baker’s cyst.

Common causes:

• Knee osteoarthritis

• Cartilage damage or degeneration

What Causes Swelling Behind the Knee?

The most common reason for swelling behind the knee is a Baker’s cyst. It occurs when excess joint fluid herniates into the back of the knee. As the cyst enlarges, it may cause pressure, stiffness, and pain.

However, not all posterior knee swellings are Baker’s cysts. Other possible causes include:

• Popliteal vein insufficiency (varicose veins)

• Enlarged lymph nodes

• Tumors or other soft-tissue masses

A key distinguishing feature of a Baker’s cyst is that it tends to shrink or disappear when the knee is bent. Diagnosis is easily confirmed by ultrasound or MRI.

If the cyst is large, causing pressure, or linked to a serious underlying condition, treatment is needed. Otherwise, monitoring may be sufficient.

Can a Baker’s Cyst Burst?

Although rare, a Baker’s cyst can rupture, causing fluid to leak down into the calf area. This can result in:

• Sudden, severe pain and swelling behind the knee

• Calf swelling

• Redness and a sensation of fluid trickling down toward the ankle

Is There a Link Between a Baker’s Cyst and Blood Clots?

There is no direct link. However, if a Baker’s cyst ruptures, it can mimic the symptoms of a deep vein thrombosis (DVT), such as:

• Intense calf pain

• Swelling

• Redness

If these symptoms occur, you should be evaluated for possible blood clots.

How Is a Baker’s Cyst Diagnosed?

Baker’s cyst is often diagnosed through a physical exam. However, since its symptoms may resemble more serious conditions such as blood clots, aneurysms, or tumors, imaging tests like ultrasound or MRI are often recommended for accurate diagnosis.

Baker’s Cyst Treatment Options

In some cases, a Baker’s cyst may resolve on its own. However, if it is large or painful, the following treatments may be helpful:

Ultrasound-Guided Cortisone Injection

The cyst is aspirated (drained) using a needle under ultrasound guidance. A cortisone injection may then be administered into the cyst to reduce inflammation and help prevent recurrence.

Treat the Underlying Cause

The key to long-term relief is addressing the root cause of excessive joint fluid production. If the cyst is caused by knee osteoarthritis, treating the arthritis — for example, with total knee replacement — can lead to resolution of the cyst.

Surgical removal of the cyst is rarely required.

Conclusion

Swelling behind the knee is not always caused by a simple issue. Even a common Baker’s cyst may be a sign of a deeper problem such as a meniscus tear, arthritis, or autoimmune disease.

In rare cases, swelling could be due to more serious issues like vascular enlargement, muscle bleeding, or blood clots. If your swelling persists, increases in size, or is accompanied by pain, consult an orthopedic specialist promptly.

Early diagnosis shortens treatment time and prevents complications. Don’t ignore your knee health — take proactive steps to protect your mobility.

To learn the cause of your knee swelling and discover personalized treatment options, contact Op. Dr. Utku Erdem Özer today. Take your first step toward healthier, pain-free movement.