Noticed a soft, sometimes painful lump behind your knee? It could be a Baker’s cyst, a fluid-filled sac that can cause swelling, tightness and discomfort at the back of the knee. These are common and usually not dangerous, but they are almost always a sign of something else going on in the knee.
In this guide we explain what a Baker’s cyst is, how to know if you have one, what causes the knee pain and swelling, and how physiotherapy helps by treating the underlying cause.
What Is a Baker’s Cyst?
Also called a popliteal cyst, it is a fluid-filled swelling that forms behind the knee. It happens when the knee produces excess joint fluid, which collects in a sac at the back of the joint. The result is a soft lump behind the knee that can feel tight, especially when you bend or straighten the leg. It is named after the doctor who first described it.
What Causes a Baker’s Cyst?
Here is the key thing to understand: it is usually a symptom, not the root problem. It forms when something inside the knee, such as arthritis, a meniscus tear or another source of irritation, makes the joint produce extra fluid, sometimes alongside knee pain. That fluid backs up into the cyst. This is why treating the cyst alone often is not enough, the underlying knee issue is what really needs addressing.
Signs You Have a Baker’s Cyst
How do you know if it is the cause? The classic signs are a soft lump or swelling behind the knee, a feeling of tightness or fullness, and sometimes knee pain that worsens with activity or when fully bending the leg. The swelling may become more obvious when standing. Some cysts cause little trouble, while others are uncomfortable, particularly if the underlying knee problem and knee pain flare.
How Is It Diagnosed?
It can often be identified from your symptoms and a physical examination. Because it usually points to an underlying knee issue, your physiotherapist or doctor will also look at what is driving it. Sometimes imaging like an ultrasound or MRI is used to confirm the cyst and, importantly, to check what is happening inside the knee itself.
How a Baker’s Cyst Is Treated
Treatment focuses on the cause, not just the cyst. Since it usually stems from an underlying knee problem, addressing that, through physiotherapy to settle irritation and knee pain, restore movement and build strength, often helps the cyst settle too. Managing swelling and activity helps in the meantime. Draining the cyst or surgery is occasionally considered by a doctor, but if the underlying issue remains, the cyst can return, which is why physiotherapy-led management is usually the smarter first step.
When to Seek Urgent Help
Occasionally a cyst can burst, leaking fluid down into the calf. This can cause sudden calf pain, swelling and redness, which can look just like a blood clot, or DVT. Because a DVT is serious, if you develop sudden calf pain, swelling, warmth or redness, seek prompt medical assessment to rule it out. It is uncommon, but worth knowing.
Can You Exercise With One?
In most cases, yes, and appropriate exercise is often part of the solution. Because it is usually linked to an underlying knee issue, the right strengthening and movement, guided by a physiotherapist, can help settle the knee and the cyst. Avoid pushing into sharp knee pain, and let your physiotherapist tailor activity to your knee. Staying active generally beats resting completely.
Common Questions About Baker’s Cysts
What causes a Baker’s cyst?
It usually forms because of an underlying knee problem, like arthritis or a meniscus tear, that makes the joint produce extra fluid. That fluid collects in a sac behind the knee.
Will it go away on its own?
Sometimes, especially if the underlying knee issue settles. Treating the cause with physiotherapy gives the best chance of it resolving and not returning.
Is it serious?
Usually not. It is mostly a nuisance rather than dangerous. The main thing to watch for is a burst cyst causing calf symptoms that mimic a clot, which needs prompt medical checking.
How is a Baker’s cyst treated?
By treating the underlying knee problem, usually with physiotherapy to settle irritation and build strength. Draining or surgery is occasionally used but the cause still needs addressing.
Can I exercise with one?
Usually yes. Guided exercise often helps by improving the underlying knee issue. Avoid sharp knee pain and get a physiotherapist to tailor your activity.
How BeFit Can Help
At BeFit Training Physiotherapy, we help you get to the bottom of the problem by treating the knee issue behind it. Our general physiotherapy and sports physiotherapy teams assess your knee, settle the irritation and build the strength to keep it healthy, and a mobility assessment can pinpoint what is driving the cyst. Initial consultations run for 45 minutes, one-on-one.
Our team at Edgecliff and Coogee would be glad to help. No referral is required, and HICAPS is available on-site for immediate health fund claiming.
Book an appointment at BeFit Training Physiotherapy — no referral needed.
Edgecliff: (02) 9327 7749 | Coogee: (02) 7205 2805 | befittrainingphysio.com/book-now
Related Services at BeFit
Learn more about how our team can help:
General Physiotherapy
Sports Physiotherapy
Mobility Assessment
Further Reading
How to Know If Your Knee Pain Needs a Physiotherapist
How to Treat a Meniscus Tear Without Surgery
References
Frush TJ, Noyes FR. Baker’s cyst: diagnostic and surgical considerations. Sports Health. 2015.
Herman AM, Marzo JM. Popliteal cysts: a current review. Orthopedics. 2014.
Australian Physiotherapy Association. Clinical guidelines. physiotherapy.asn.au.
