What is a Baker’s cyst?

A Baker’s cyst is a fluid-filled swelling that develops behind the knee, usually because excess fluid from the knee joint collects in a small space between two tendons. It is also known as a popliteal cyst and is generally benign.

In adults, Baker’s cysts are commonly associated with an underlying knee problem that causes inflammation or excess joint fluid. These may include osteoarthritis, meniscal tears, rheumatoid arthritis, gout or a previous knee injury.

Consultant orthopaedic surgeon Mr Paul Haslam has a particular interest in the surgical treatment of Baker’s cysts, including keyhole surgery for persistent, symptomatic cysts.

What are the symptoms of a Baker’s cyst?

A Baker’s cyst may cause a soft lump behind the knee, although some people have no symptoms at all. Symptoms can become more noticeable after walking or other activities that place stress on the knee.

Common symptoms include:

• A noticeable swelling or lump behind the knee.
• Pain, aching or tightness around the knee.
• Stiffness or difficulty fully bending the knee.
• A feeling of pressure behind the knee.
• Clicking or other symptoms caused by the underlying knee problem.

The size of the cyst can vary, and symptoms are not necessarily related to its size. In some cases, a cyst can rupture, causing fluid to move into the calf and producing sudden pain and swelling that can resemble a deep vein thrombosis (DVT).

What causes a Baker’s cyst?

A Baker’s cyst usually develops when a knee condition causes increased production of synovial fluid, which is the fluid that lubricates the joint. The additional fluid can pass through an opening at the back of the knee and collect between the semimembranosus tendon and medial head of the gastrocnemius muscle.

Common underlying causes include:

• Osteoarthritis and other forms of arthritis.
• Meniscal tears or other cartilage damage.
• Knee injuries.
• Inflammatory conditions such as rheumatoid arthritis.
• Gout and other causes of inflammation within the knee.

Treating the underlying knee condition is therefore an important part of managing a symptomatic Baker’s cyst and can reduce the likelihood of the cyst returning.

How is a Baker’s cyst diagnosed?

A Baker’s cyst can often be diagnosed through a physical examination and ultrasound, although further imaging may be required to investigate the knee itself. Ultrasound can identify the fluid-filled cyst and help distinguish it from other causes of swelling behind the knee.

An MRI scan may be recommended when more detailed assessment is needed. It can identify the cyst as well as associated problems such as meniscal tears, cartilage damage, osteoarthritis or ligament injuries.

How is a Baker’s cyst treated?

Treatment depends on the severity of symptoms and the underlying cause, and many Baker’s cysts do not require direct treatment. Management generally focuses on controlling symptoms and addressing the knee problem responsible for the excess fluid.

Treatment options may include:

• Rest and modification of activities that aggravate symptoms.
• Pain relief and anti-inflammatory medication where appropriate.
• Physiotherapy to maintain knee movement and strength.
• A corticosteroid injection into the knee to reduce inflammation.
• Aspiration, where fluid is drained from the cyst in selected cases.
• Surgery to treat an underlying knee problem when conservative treatment is unsuccessful.

For most people, a Baker’s cyst does not need surgery. However, a persistent cyst that causes pain, pressure or restricted movement despite appropriate treatment may warrant a specialist assessment.

Aspiration can be useful to see if the symptoms are cyst related or due to other knee pathology. Needle aspiration is rarely successful and the cyst will almost always recur.

Mr Paul Haslam has performed more than 70 arthroscopic Baker’s cyst procedures and has presented his results at BOSTAA in 2024. Using a keyhole approach, he can assess and treat the cyst and its connection to the knee joint, while also addressing relevant problems within the knee where appropriate. This approach uses small incisions rather than the larger incision associated with open cyst surgery. Treatment is tailored to the individual, with a success rate of 93%.

What can you do to manage a Baker’s cyst?

Practical measures can help reduce discomfort while the cyst and its underlying cause are being managed. These include:

• Resting the knee and temporarily reducing aggravating activities.
• Applying a wrapped ice pack for around 10 minutes at a time.
• Elevating the leg to help reduce swelling.
• Taking appropriate pain relief if needed.
• Following an exercise or physiotherapy programme recommended by a healthcare professional.

A Baker’s cyst can take several months, and sometimes longer, to settle, particularly when an underlying knee condition remains active.

When should you seek medical help for a Baker’s cyst?

You should seek medical assessment for an unexplained lump behind the knee, particularly if it is painful, enlarging or affecting movement. Although Baker’s cysts are usually harmless, other conditions can cause similar swelling and need to be excluded.

Urgent medical assessment is important if there is sudden or worsening pain and swelling in the calf, particularly with warmth, redness or bruising, as a ruptured cyst can resemble a DVT. If leg swelling or pain is accompanied by chest pain or breathlessness, emergency medical attention is required because these can be symptoms of a pulmonary embolism.

If you are experiencing symptoms or have concerns about your knee, visit Mr Paul Haslam’s Top Doctors profile to book a consultation.

References

• NHS: Baker’s cyst
• Noyes FR, et al. Baker’s Cyst: Diagnostic and Surgical Considerations. Sports Health.
• Nanduri A, et al. Baker's Cyst. Cureus.
• Diagnostic accuracy of ultrasound for the assessment of Baker’s cysts: a meta-analysis. Journal of Orthopaedic Surgery and Research.