Pain or a lump behind the knee (Baker's cyst): what it is and when it matters
What a Baker's cyst is, how it feels, what usually causes it, and the warning signs that can mean a burst cyst or a blood clot.
A Baker's cyst is a soft, fluid-filled lump at the back of the knee. The NHS says that in adults it usually develops when another knee problem, such as an injury or arthritis, has damaged the joint. It can be uncomfortable, but it often does not need treatment, and it is important to know the signs that point to something more serious in the calf.
When to get urgent help
Go to A&E or call 999 if you have any of these. They can be signs of a fracture, infection, blood clot or other emergency.
- A limb that looks deformed, or a joint that you cannot move or put weight on after an injury
- A cold, pale or numb foot or hand after injury
- A hot, red, swollen joint with a high temperature
- A painful, swollen, warm calf, with or without breathlessness or chest pain
What it can feel like
- A soft lump at the back of the knee, which may be more obvious when you stand
- Knee or leg pain, tightness or stiffness, and difficulty bending the knee
- Clicking in the knee, and symptoms that worsen after walking
Common contributors
- In adults it usually follows another knee problem such as an injury, osteoarthritis, rheumatoid arthritis or gout
- It is more common in people aged 35 to 70
- In children there is often no clear cause
General self-care
These are general comfort measures many people find reasonable. They are not a treatment plan, and what suits one person may not suit another.
- The NHS suggests resting the knee and raising the leg on a pillow
- An ice pack wrapped in a tea towel for around 10 minutes at a time can ease discomfort
- Ibuprofen or paracetamol can help with pain and swelling, if suitable for you. Ask a pharmacist if unsure
- Often the cyst does not need treatment and may go away on its own, but recovery can take months to years
When to see your GP
See your GP promptly, or call NHS 111, if you have any of the following:
- Pain after a significant injury, fall or twist
- Pain that is constant, severe or getting worse, or wakes you at night
- Unexplained weight loss, fever or feeling generally unwell with limb pain
Consider seeing your GP if:
- Any lump you cannot explain, anywhere on your body. See your GP
- Sudden worsening leg pain or swelling, swelling with bruising and warm skin, or red or darkened skin. These can mean a burst cyst or a blood clot (DVT). Get an urgent GP appointment or call NHS 111
- Leg pain or swelling together with breathlessness or chest pain. This may be a clot in the lung. Call 999 or go to A&E, and do not drive yourself
Where an osteopath fits in
There is limited good-quality research showing that hands-on treatment changes the course of a Baker's cyst, so I do not claim that osteopathy treats it.
What an osteopath can usefully do is examine the knee to look for the underlying cause, and, if the knee is stiff or weak, help with movement and strengthening. Anything that could be a burst cyst or a blood clot needs medical care first. The NHS says a GP may arrange an ultrasound or MRI scan to check. If the assessment suggests you need your GP, a physiotherapist or a specialist instead, I will tell you.
If you would like your symptoms assessed, you are welcome to book an appointment. Osteopathic care is not right for everyone, and if something needs medical attention first, I will tell you.
Common questions
Is a Baker's cyst serious?
The NHS says it often does not need treatment and may resolve on its own. The concern is a burst cyst or a blood clot, which can look similar. Sudden worsening pain or swelling, warm or discoloured skin, or breathlessness need urgent medical attention.
How do I tell a Baker's cyst from a blood clot?
You cannot reliably tell by looking. A clot (DVT) usually causes a swollen, painful, warm calf, often on one side. If you have these signs, get urgent medical advice. With breathlessness or chest pain, call 999.
Sources and further reading
Links open in a new tab. Sources were checked in October 2026.
Related guides
This page is general information to help you understand common aches and pains. It is not medical advice and cannot diagnose your problem. If you are worried about your symptoms, please speak to your GP or call NHS 111.