A Baker's cyst (popliteal cyst) is a fluid-filled swelling at the back of the knee [1]. In adults it usually forms when another knee problem, such as knee osteoarthritis or a meniscal tear, makes the joint produce excess fluid; treatment is therefore aimed first at that problem [2][3]. It may go away by itself; however, pain and swelling in the calf that suddenly get worse can be a sign of a burst cyst or of a blood clot in the leg and should be assessed without delay [1][2].
What is a Baker's cyst and what causes it?
A Baker's cyst is a fluid-filled swelling at the back of the knee [1]. The fluid inside it is the joint fluid that lubricates the knee; it collects in a sac on the inner side of the back of the knee [2][3][4].
In adults it is usually the result of an injury or a condition that causes swelling and inflammation in the knee joint [2]. The knee produces excess joint fluid; the fluid passes to the back of the knee through an opening that works like a one-way valve, cannot return, and collects there [2][3]. In adults up to 94% of cysts are accompanied by a problem inside the joint; the most frequent accompanying problem is a meniscal tear [3].
In younger patients and children there is often no identifiable cause [2][4]. The main conditions that can lead to a cyst are [1][2]:
- Knee osteoarthritis
- Rheumatoid arthritis
- A meniscal tear
- A tear of the anterior cruciate ligament
- Gout
- Knee injuries and other conditions that damage the tissues inside the joint
What are the symptoms?
Some Baker's cysts cause no symptoms at all and are noticed by chance, during an examination or on an MRI scan done for another reason [2]. Most symptoms come from the underlying meniscal or cartilage problem; symptoms caused by the cyst itself are infrequent [3].
Symptoms may be worse after walking [1]. The symptoms that may occur are [1][2]:
- A soft lump or a feeling of fullness behind the knee
- Knee or leg pain
- Tightness, stiffness or aching at the back of the knee
- Difficulty bending the knee
- Clicking in the knee
- Swelling in the knee and lower leg
How is it recognised and diagnosed?
The doctor takes your history and examines the knee, comparing it with the other knee [2]. The cyst often feels firm when the knee is straight and soft when the knee is bent [2][3].
Not every swelling behind the knee is a Baker's cyst: a ganglion cyst, a widened artery (aneurysm) and tumours can also form a lump in this area; with these, the feel of the lump does not change with the position of the knee [3]. Other causes of knee pain are covered in the article on knee pain.
An X-ray does not show the cyst, but it reveals accompanying problems such as osteoarthritis [2][3]. Ultrasound shows whether the swelling is filled with fluid or is solid; it is inexpensive, involves no radiation and is used for the initial assessment [2][3]. MRI is the most detailed method for telling the cyst apart from other lumps and for showing the underlying problem, such as a meniscal tear [3].
Does it go away by itself, and how long does it take?
A Baker's cyst does not always need treatment; it may get better by itself or by treating the condition that causes it [1]. According to the American Academy of Orthopaedic Surgeons (AAOS), most Baker's cysts go away on their own [2]. Getting better can take from a few months to a few years; improvement without treatment is seen particularly in children [1]. A cyst that causes no symptoms can simply be observed [2].
In adults the cyst is a consequence of increased fluid in the joint; as long as the problem that increases the fluid continues, the cyst can fill up again [3][4]. Treatment is therefore aimed at the underlying knee problem rather than at the cyst itself [1][3].
What can be done at home? Exercises and creams
The patient pages of the National Health Service in England (NHS) and the AAOS do not give a specific home programme of exercises for a Baker's cyst [1][2]. Physiotherapy is among the treatments a doctor may offer [1]; its aim is to maintain the range of movement of the knee and strengthen the muscles around it [2][3]. Cutting down high-impact activities such as jogging and aerobics can ease symptoms [2].
Creams for a Baker's cyst are also a frequent question: the NHS and the AAOS do not list a cream, gel or ointment among the treatments, and the sources reviewed contain no data showing that any cream shrinks the cyst [1][2][3][4].
To ease pain and swelling, the following can be done at home [1]:
- Resting the knee
- Applying an ice pack wrapped in a towel to the knee for around 10 minutes at a time
- Raising the leg, for example by resting it on a pillow
- Taking a painkiller for pain and swelling; you can ask your pharmacist or doctor which one is suitable for you
Draining the cyst and cortisone injection
The treatments a doctor may offer include painkillers, a cortisone (steroid) injection into the knee, physiotherapy and draining the fluid from the cyst [1]. A cortisone injection into the joint has been reported to reduce the size of the cyst and the symptoms [3].
How is the cyst drained? The area around the cyst is numbed and the excess fluid is drawn off with a needle (aspiration), often under ultrasound guidance [2]. Cortisone is then often injected into the cyst or into the joint [4].
In a study of 26 people with a Baker's cyst due to knee osteoarthritis, pain decreased and the cyst became smaller in the four weeks after draining and a cortisone injection, whereas stiffness and function scores did not change significantly [5]. Draining can ease symptoms; however, when the osteoarthritis or meniscal problem persists, it is common for the cyst to fill up again [4].
Surgery: when and how is a Baker's cyst removed?
Surgery for a Baker's cyst is rarely needed [1][2]. It may be recommended if painful symptoms persist despite non-surgical treatment or if the cyst fills up again after repeated draining [2].
Surgery, too, is aimed first at the cause inside the joint: in one older series in which only the cyst was removed, the cyst re-formed after 63% of 46 operations [3]. In arthroscopy (keyhole surgery) the problems inside the joint that give rise to the cyst are treated; during the same procedure the valve between the cyst and the joint can be opened, which may keep the cyst from re-forming [2].
Not every problem inside the joint is corrected by surgery, however: an international guideline makes a strong recommendation against arthroscopy in nearly all patients with degenerative knee disease (osteoarthritis and degenerative meniscal tears) [6].
For large cysts, or cysts pressing on blood vessels and nerves, the whole cyst may be removed by open surgery [2]. Most patients return to all their activities around 4 to 6 weeks after surgery [2].
Why does a burst Baker's cyst resemble a blood clot in the leg?
It is uncommon for the cyst to burst [2][4]. When it does, the joint fluid inside spreads between the calf muscles; there is sudden pain, swelling and tightness in the calf [4].
This picture closely resembles a blood clot forming in a leg vein (deep vein thrombosis, DVT): DVT also causes throbbing pain, usually in one leg, with swelling and red or darkened skin [7]. Telling the two apart by examination alone is often not possible; for this reason the veins are first checked with ultrasound to rule out a clot [3][4]. The distinction matters because in DVT the clot can travel to the lungs [7].
A burst cyst usually settles by itself; the fluid that has spread into the calf is reabsorbed over time [4]. Symptoms are worse than normal until the swelling goes down, which can take a few weeks [1].
When not to wait
If pain and swelling in the leg are accompanied by breathlessness or chest pain, this can be a sign of a blood clot that has travelled to the lungs (pulmonary embolism); go to an emergency department or call an ambulance immediately [1][7].
If you have a lump on your body and do not know what it is, show it to a doctor [1]. The following can be signs of a burst cyst or of a blood clot in the leg. The two cannot be told apart without assessment; seek care without waiting [1][2][4]:
- Pain or swelling in the leg has suddenly got worse
- There is swelling, bruising and warm skin on the leg
- The skin on the leg has become red or darkened (this can be harder to see on brown or black skin)
- The swelling in the leg is getting harder or softer
Frequently asked questions
- How does a Baker's cyst go away?
- Treatment is not always needed; the cyst may get better by itself or by treating the knee problem that causes it [1]. Rest, ice, raising the leg and painkillers ease symptoms; if needed, a cortisone injection, physiotherapy or draining of the cyst is used [1][2].
- How long does a Baker's cyst take to go away?
- Getting better can take from a few months to a few years [1]. With a burst cyst the swelling can take a few weeks to go down [1].
- How is a Baker's cyst drained?
- The area around the cyst is numbed and the fluid is drawn off with a needle; the procedure is often done under ultrasound guidance [2]. If the underlying knee problem persists, it is common for the cyst to fill up again [4].
- Does a cream or exercise help a Baker's cyst?
- The NHS and the AAOS do not list a cream among the treatments [1][2]. Physiotherapy is one of the treatment options; the aim of the exercises is to maintain the range of movement of the knee and strengthen the surrounding muscles, but these sources do not give a specific home programme [1][2].
- What happens if a Baker's cyst bursts?
- The fluid spreads into the calf; there is sudden pain and swelling in the calf, and it usually settles by itself within weeks [1][4]. Because the same symptoms occur with a blood clot in the leg, you need to be assessed without waiting; if there is breathlessness or chest pain, go to an emergency department [1][7].
This article is a general summary; diagnosis and treatment decisions are made by the doctor who examines you.
Sources
- Baker's cyst. NHS (nhs.uk), 2025. nhs.uk
- Baker's Cyst (Popliteal Cyst). American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
- Baker's Cyst: Diagnostic and Surgical Considerations. Sports Health (Frush TJ, Noyes FR), 2015. pubmed.ncbi.nlm.nih.gov
- Ruptured Baker's Cyst Demystified: Current Evidence, Diagnostic Strategies, and Treatment Options for an Under-Recognized Condition. Cureus (Zmerly H, et al.), 2026. pubmed.ncbi.nlm.nih.gov
- Ultrasound-guided aspiration and corticosteroid injection of Baker's cysts in knee osteoarthritis: a prospective observational study. American Journal of Physical Medicine & Rehabilitation (Di Sante L, et al.), 2010. pubmed.ncbi.nlm.nih.gov
- Arthroscopic surgery for degenerative knee arthritis and meniscal tears: a clinical practice guideline. BMJ (Siemieniuk RAC, et al.), 2017. pubmed.ncbi.nlm.nih.gov
- DVT (deep vein thrombosis). NHS (nhs.uk), 2026. nhs.uk
This article is general information and does not replace an examination or imaging. If you have symptoms, see a doctor.
More in this area
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- Cartilage damage in the knee: does cartilage heal, and how is it treated?
- Knee injections: what do cortisone, hyaluronic acid, PRP and stem cells do?
- Knee osteoarthritis: exercise, weight, injections and replacement, what and when?
- Knee pain: what causes it, what helps and who should you see?
- Knee replacement surgery: who is it for and what is recovery like?
- Meniscus tear: exercise or arthroscopy?
- Kneecap pain and chondromalacia patella: what causes it and how does it settle?