Baker cyst

Overview

A Baker cyst is a fluid-filled swelling that forms behind the knee. It happens when extra fluid from the knee joint bulges out into the back of the knee, often because of a knee problem like arthritis or a torn cartilage.

It is fairly common, especially in adults over 40 who have knee conditions like arthritis.

Baker cysts most often affect adults with knee arthritis or a knee injury. They are less common in children, but can occur with juvenile arthritis.

Symptoms

Common symptoms

• A bump behind the knee
• Feeling of tightness or pressure behind the knee
• Pain when bending or straightening the knee
• Swelling in the lower leg if the cyst bursts

Symptoms in children

• Similar swelling behind the knee, often linked to juvenile arthritis
• May cause discomfort but usually not severe pain

Symptoms in older adults

• The cyst may be larger and more noticeable due to underlying arthritis
• Pain or stiffness behind the knee, especially after activity

Causes

Main causes

• Excess fluid from the knee joint due to osteoarthritis
• A tear in the meniscus (cartilage) of the knee
• Rheumatoid arthritis or gout affecting the knee
• Other conditions that cause knee swelling, such as infection (rare)

Risk factors

• Being over 40 years old
• Having osteoarthritis or rheumatoid arthritis
• Previous knee injury or surgery
• Participating in sports that stress the knee, like running or jumping

When to see a doctor

See a doctor urgently if:

• If you have a sudden, painful swelling in your calf that feels warm or looks red
• If you have difficulty walking or putting weight on your leg

Book a routine appointment if:

• A painless lump behind your knee that does not go away after a few weeks
• Mild pain or stiffness behind the knee that bothers you
• If you have a known knee condition and notice a new lump

Diagnosis

Your doctor will ask about your symptoms and examine your knee. They may shine a light through the lump (transillumination) to check if it’s fluid-filled. If needed, they will order an imaging test to confirm the diagnosis and rule out other problems.

Tests that may be done

• Ultrasound – a sound wave picture that shows if the lump is a fluid-filled cyst
• MRI – a detailed scan that can see the cyst and any underlying knee damage

What to expect at your appointment

The doctor will press gently behind your knee and might ask you to bend and straighten it. If you have pain or swelling, they may recommend imaging. The process is straightforward and usually not painful.

Treatment

Treatment focuses on relieving symptoms and addressing the underlying knee condition. Many Baker cysts do not need active treatment. If they cause discomfort, the options include self-care, draining the fluid, or treating the root cause like arthritis or a meniscal tear.

Self-care at home

• Rest your knee and avoid activities that cause pain, like running or squatting
• Apply ice to the back of your knee for 15–20 minutes a day to reduce swelling
• Elevate your leg when sitting or lying down
• Do gentle range-of-motion exercises, like straightening and bending your leg

Medical treatments

A doctor may drain the fluid from the cyst using a needle (aspiration), often with ultrasound guidance. They may also give a steroid injection into the knee to reduce inflammation. Treating the underlying knee problem, such as with pain relievers or physical therapy, can also help the cyst shrink.

When is surgery considered?

Surgery is rarely needed for the cyst itself. If the cyst comes from a meniscus tear or another knee problem that requires surgery, fixing that issue often makes the cyst go away.

Living with this condition

Most people with a Baker cyst can continue their normal daily activities. If the cyst causes pain, you may need to take breaks and modify movements that bend the knee deeply.

Lifestyle tips

• Choose low-impact exercises like swimming, cycling, or walking on flat ground
• Avoid high-impact activities like running or jumping until the cyst resolves
• Use supportive shoes to reduce knee strain

Diet and exercise

Eating a well-balanced diet can help maintain a healthy weight, which reduces stress on your knees. Gentle stretching and strengthening exercises for your thigh and calf muscles can support the knee joint.

Mental health and emotional wellbeing

Living with knee pain or a visible lump can be frustrating or worrying. It’s normal to feel concerned. Talk to your doctor or a counsellor if you feel anxious or down about your condition.

Prevention

There is no sure way to prevent a Baker cyst, but managing knee conditions like arthritis and avoiding knee injuries may lower your risk. Keeping your leg muscles strong and maintaining a healthy weight can also help.

Complications

If left untreated

• The cyst may rupture, causing sudden pain and swelling in the calf (this is usually not dangerous but can be uncomfortable)
• Rarely, the cyst can become infected (septic bursitis), causing redness, warmth, and fever
• The cyst may come back after draining if the underlying knee problem is not treated

Long-term outlook

The outlook for a Baker cyst is very good. Most cysts either go away on their own or with simple treatment. Even if it comes back, it can be managed. The underlying knee condition may need long-term care, but the cyst itself is rarely a serious problem.

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