Bakers Cyst

Overview

A Baker's cyst is a fluid-filled swelling at the back of the knee. It happens when fluid from the knee joint leaks out and collects in a small sac behind the knee. It is usually a sign of a problem inside the knee, such as arthritis or a cartilage tear, and is not a type of cancer.

Yes, Baker's cysts are fairly common, especially among people over 40 with knee problems like osteoarthritis or rheumatoid arthritis.

It most often affects adults over 40, especially those with knee arthritis. Children can also get Baker's cysts, often linked to a knee injury or other knee condition.

Symptoms

Common symptoms

• A soft bulge or swelling behind the knee
• Tightness or fullness in the back of the knee
• Mild pain or discomfort when bending or straightening the knee
• Stiffness, especially after sitting or resting
• The bulge may feel larger after activity or when the knee is straight

Symptoms in children

• A small, painless lump at the back of the knee
• The lump may come and go over time
• Usually no other symptoms unless the knee itself is injured

Symptoms in older adults

• More noticeable swelling, often linked to arthritis
• Pain and stiffness in the knee, especially when active
• The cyst may feel large and cause difficulty bending the knee

Causes

Main causes

• Extra fluid builds up in the knee joint due to inflammation or damage
• Fluid pushes out from the joint into the back of the knee, forming a cyst
• Common underlying conditions include osteoarthritis, rheumatoid arthritis, gout, and injuries to the knee cartilage

Risk factors

• Being over 40
• Having osteoarthritis or rheumatoid arthritis
• Having a previous knee injury or surgery
• Repeated activity that stresses the knee

When to see a doctor

See a doctor urgently if:

• Sudden, severe leg or calf pain that worsens
• Red, hot, or extremely swollen leg with fever
• Difficulty breathing or chest pain (call emergency services)
• The knee gives way or you cannot bear weight on it

Book a routine appointment if:

• A persistent lump at the back of the knee that does not go away
• Pain or stiffness that affects your daily activities
• Swelling that keeps worsening after rest and ice

Diagnosis

A doctor will ask about your symptoms, examine your knee and calf, and feel for a soft swelling behind the knee. They may shine a light against the swelling or ask you to bend and straighten your knee to check how the lump changes.

Tests that may be done

• Usually no tests are needed if the doctor is confident it is a Baker's cyst
• An ultrasound scan can confirm the cyst and check the surrounding tissues
• Sometimes an MRI is used to look for a tear in the knee cartilage if symptoms are unclear

What to expect at your appointment

The examination is simple and painless. If the doctor is not sure about the swelling, they may recommend an ultrasound or arrange a referral to a specialist. Most of the time, you will not need imaging.

Treatment

Treatment depends on the cause and whether the cyst is causing symptoms. Often the best approach is to manage the underlying knee problem, such as arthritis or a cartilage injury, and give the cyst time to shrink. Treatment is usually conservative and does not require surgery.

Self-care at home

• Rest the knee and avoid activities that cause sharp pain
• Apply ice wrapped in a towel to the back of the knee for 15–20 minutes several times a day
• Keep the leg elevated when sitting to help fluid drain away
• Use a compression bandage for short periods if it feels comfortable and does not make symptoms worse
• Do gentle range-of-motion exercises as pain allows to keep the knee moving

Medical treatments

For pain and swelling, a pharmacist or doctor can suggest a suitable anti-inflammatory medicine (always follow the advice of a healthcare professional). Physiotherapy to strengthen the thigh muscles can improve knee function and reduce fluid production. If the cyst is large and painful, a doctor may drain the fluid with a needle (aspiration) and may inject a steroid into the knee to reduce inflammation — these are done in a clinic setting.

When is surgery considered?

Surgery is rarely needed. It may be considered when a Baker's cyst keeps coming back because of a specific treatable problem inside the knee, such as a torn meniscus. In that case, treating the knee problem itself usually helps the cyst resolve.

Living with this condition

Most Baker's cysts cause little trouble. Keep moving the knee gently and avoid long periods of standing or sitting. Use ice after activity if the knee feels tight. Watch for any sudden changes in your calf, and contact your doctor if the leg becomes painful or swollen.

Lifestyle tips

• Maintain a healthy weight to reduce strain on the knee
• Choose low-impact activities like swimming, cycling, or walking on flat ground
• Allow time for rest and avoid overloading the knee

Diet and exercise

A balanced diet helps with overall joint health. Regular, gentle exercise keeps the knee mobile and strengthens the muscles around it. Talk to a physiotherapist about a safe exercise plan if you are unsure.

Mental health and emotional wellbeing

Living with knee pain can be frustrating, but remember a Baker's cyst is usually not dangerous and often settles by itself. If pain or restricted movement affects your mood or daily life, speak honestly with your doctor about your concerns.

Prevention

There is no guaranteed way to prevent a Baker's cyst because it usually forms as a response to knee inflammation. However, protecting your knees, treating arthritis early, and avoiding repeated knee injuries can lower the chance that fluid collects behind the knee.

Complications

If left untreated

• Most of the time there are no complications
• Rarely, the cyst can rupture, causing sharp calf pain, redness, and swelling on the lower leg – this is alarming but usually settles with rest and care
• If the underlying knee problem is not managed, the cyst may remain or come back
• Very rarely, a large cyst can press on nearby structures, causing discomfort or problems with bending the knee

Long-term outlook

The outlook is generally very good. Baker's cysts often shrink or disappear once the knee problem that caused them is treated. Even if it takes time, it is rarely a serious condition and does not lead to cancer or permanent knee damage on its own.

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