Baker's Cyst (Popliteal Cyst)

What is a Baker's cyst?

A Baker's cyst — also called a popliteal cyst — is a fluid-filled swelling at the back of the knee. It develops when fluid from inside the knee joint pushes its way into a small pouch behind the joint.

In most cases, a Baker's cyst is a sign of something else going on inside the knee — often osteoarthritis, a meniscal tear or another condition that's causing extra fluid to accumulate. The cyst itself is the visible consequence rather than the underlying problem.

Baker's cysts can vary considerably in size, from small and barely noticeable to large enough to be visibly obvious. They can also fluctuate over time, growing and shrinking depending on what's happening inside the knee.

What does it feel like?

Symptoms vary widely. Some Baker's cysts cause no symptoms at all and are noticed by chance. Others produce:

• A visible or palpable lump behind the knee

• A feeling of tightness or pressure when bending the knee

• Discomfort when squatting, kneeling or sitting in some positions

• A sense that the knee is full or swollen

• Pain that's actually coming from the underlying knee problem rather than the cyst itself

Occasionally a Baker's cyst can rupture, causing sudden swelling and pain in the calf — this can mimic a deep vein thrombosis and warrants assessment to distinguish the two.

How is it diagnosed?

Examination usually reveals a swelling at the back of the knee, particularly when the knee is straight. The cyst tends to soften when the knee is bent.

Ultrasound is the most useful imaging — it confirms the diagnosis, assesses size and rules out other causes of swelling at the back of the knee. MRI is sometimes useful when the underlying knee condition needs further assessment.

Critically, the assessment must consider what's driving the cyst. Treating the cyst in isolation without addressing the underlying problem rarely produces lasting results.

What are the treatment options?

In many cases, treating the underlying knee condition is the most effective approach — when the inside of the knee is calmer, the cyst often shrinks on its own.

Direct treatment of the cyst itself — aspiration with or without injection — can provide relief but isn't always lasting if the underlying cause hasn't been addressed. Surgical removal is uncommon and reserved for specific situations. Nev will work through the right approach for your case at your consultation.

When should you get it checked?

Seek a specialist assessment if:

• There's a noticeable swelling at the back of the knee

• The cyst is causing pain or limiting movement

• There's been sudden calf swelling or pain (to exclude rupture or other causes)

• You have other knee symptoms that haven't been investigated

• You want to understand what's driving the cyst and what your options are

A Baker's cyst is rarely the whole story — and getting a clear picture of what's happening in the knee usually leads to a more satisfying outcome than treating the cyst alone.