A Baker’s cyst is a fluid-filled swelling at the back of the knee. In adults it may accompany a knee-joint problem such as osteoarthritis, inflammation or a meniscal injury. A new lump or swelling needs assessment in relation to symptoms and timing.
How might it feel?
You may notice a lump or tightness behind the knee. A larger cyst can make bending difficult. Not every cyst is painful or requires treatment.
Describe when swelling began, whether the knee itself hurts and any recent increase in activity or injury. The assessment should consider overall knee function, not only the size of the lump.
Routine assessment or more urgent contact?
| Situation | What to do in Sweden |
|---|---|
| Persistent or painful swelling behind the knee | Contact a primary care centre for examination. |
| A newly swollen, warm, tender calf on one side | Seek prompt assessment, including consideration of a blood clot. |
| Leg swelling with sudden breathlessness or chest pain | Call 112. |
Why can a ruptured cyst resemble a blood clot?
A ruptured cyst can cause pain and swelling in the calf. A blood clot can produce similar symptoms. Feeling the leg or comparing online pictures cannot reliably distinguish them. Having a previous Baker’s cyst does not exclude a new blood clot.
What might treatment target?
Your clinician considers whether symptoms mainly arise from the cyst or an underlying joint problem. Sometimes follow-up and adjusting activity are sufficient. In other cases, treatment for the knee or a procedure for the cyst may be discussed. Ask what improvement is expected and whether symptoms could recur.
Bring a short function checklist
- Can you bend and straighten the knee normally?
- What happens with walking, stairs and after rest?
- Is swelling confined behind the knee or does it involve the calf?
- Which activities do you want to return to?
Do not try to puncture or drain the swelling yourself. Ask which movements are suitable while waiting. A vårdcentral is a primary care centre. Call 1177 if symptoms change or you need help choosing the appropriate care route.
Sources and further reading
- 1177: Bakercysta – svullnad i knävecket (in Swedish)
- 1177: Blodpropp i benet eller armen (in Swedish)
- NICE: Venous thromboembolic diseases, recommendations
Sources and links checked on 22 October 2026. Editorial team: Hagakliniken. General information; individual assessment may differ.