Baker's cyst: swelling behind the knee, causes and treatment

A soft swelling or feeling of tightness at the back of the knee is often a Baker's cyst, also called a popliteal cyst. It's rarely a problem in itself; it's usually a sign that something else in the knee is irritated.

What is a Baker's cyst?

It's a fluid-filled swelling at the back of the knee. A review describes it as the enlargement of a small bursa behind the knee that connects with the knee joint, so that when the joint produces extra fluid, some is pushed into the bursa and collects there (Herman and Marzo, Orthopedics, 2014).

What causes a Baker's cyst?

In adults, it's most often linked with another knee condition that makes the joint produce more fluid. The same review notes these cysts rarely occur alone and are usually found with problems such as osteoarthritis, meniscus tears and inflammatory arthritis. In children they're usually an incidental finding and tend to resolve by themselves.

What does a Baker's cyst feel like?

A bulge or fullness behind the knee, often more noticeable when standing with the knee straight. It can cause tightness or aching, particularly with fully bending or straightening the knee, and after activity. Small cysts cause no symptoms and are found on scans done for other reasons.

When is swelling behind the knee or in the calf an emergency?

Seek same-day medical attention for a calf that is swollen, warm, red or painful, as this can be a deep vein thrombosis (blood clot). A ruptured Baker's cyst can cause sudden sharp pain behind the knee with swelling and bruising running down the calf, which looks very similar to a clot, so it needs to be checked by a doctor, usually with an ultrasound. Go to an emergency department if calf swelling comes with chest pain or breathlessness.

How is a Baker's cyst diagnosed?

Often by examination, and confirmed with ultrasound, which also helps rule out a blood clot. MRI is used when the underlying knee problem needs to be clarified. Any lump behind the knee that is hard, growing, pulsating or doesn't change with knee position should be checked by a doctor.

How is a Baker's cyst treated?

By treating what's causing the extra fluid. If the underlying knee problem settles, the cyst usually shrinks. That means managing the arthritis or meniscus irritation with activity changes, strengthening and, where appropriate, medication or an injection through your GP. The cyst itself can be drained, but it tends to refill if the cause isn't addressed. Surgery is uncommon.

Will a Baker's cyst go away by itself?

Many do, or shrink to the point of causing no symptoms, particularly once the knee calms down. Some persist and fluctuate in size with activity.

Can I exercise with a Baker's cyst?

Usually. Walking, cycling and swimming are generally fine. Avoid deep squats, kneeling and anything that forces the knee to its end of range while the cyst is large and tight. Strengthening the thigh and hip muscles helps the underlying knee problem.

What exercises help?

Gentle knee bending and straightening to maintain movement, quadriceps strengthening such as sit-to-stands and partial squats within comfort, hamstring and calf work, and hip strengthening. Progress as the knee allows.

Does ice or compression help?

Ice after activity and a compression sleeve can ease swelling and discomfort for some people. They don't treat the cause, but can make the knee more comfortable.

What happens if a Baker's cyst bursts?

The fluid tracks down into the calf, causing pain, swelling and sometimes bruising around the ankle. It isn't dangerous in itself and the fluid is reabsorbed over a few weeks, but because it mimics a blood clot it must be assessed by a doctor.

Can a Baker's cyst cause calf pain or numbness?

A large cyst can press on nearby structures, causing aching in the upper calf, a feeling of tightness, and occasionally tingling. New or severe calf pain and swelling should always be checked by a doctor to rule out a blood clot.

Is a Baker's cyst a sign of arthritis?

Often, in adults over 50, but not always. Meniscus tears and other causes of knee swelling can produce one too. Finding a cyst is a prompt to look at what's happening inside the knee.

Should I have it drained?

Draining can relieve pressure from a large, uncomfortable cyst, sometimes combined with a corticosteroid injection into the knee. Because the cyst is fed by fluid from the joint, it commonly returns unless the underlying knee problem settles. Your GP or a sports physician can advise.

How can an osteopath help?

We assess the knee to work out what's driving the swelling, refer you for an ultrasound or to your GP where needed, and treat the underlying problem with hands-on treatment and a strengthening program.

See our posts on knee osteoarthritis and meniscus irritation, or our knee and ankle pain guide. Book an assessment at our Berwick clinic. A 60-minute initial consultation is $149, with no referral needed and HICAPS on-site.

Sources

Herman AM, Marzo JM. Popliteal cysts: a current review. Orthopedics, 2014.

Book an initial consultation at RISE Sports & Spinal in Berwick. Clear diagnosis, hands-on treatment, and a plan that actually gets you better.

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