What is a Baker's cyst?
A Baker’s cyst — also known as a popliteal cyst — is a fluid-filled sac that forms at the back of the knee, in the popliteal fossa (the soft hollow behind the knee joint). It occurs when excess synovial fluid produced by the knee joint accumulates and forms a visible bulge.
Baker’s cysts are relatively common, particularly in middle-aged and older adults, and are almost always a secondary phenomenon — a symptom of an underlying knee problem rather than a condition in their own right.
What causes a Baker's cyst?
The knee joint produces synovial fluid to lubricate and nourish the joint surfaces. When the knee is irritated or damaged — due to osteoarthritis, a meniscal tear, or inflammatory arthritis — it can produce excess fluid. This excess fluid can track into a natural recess at the back of the knee and accumulate there, forming the cyst.
Common underlying causes include:
- Knee osteoarthritis — the most common cause in adults over 40
- Meniscal tears — damage to the cartilage cushions of the knee
- Rheumatoid arthritis and other inflammatory joint conditions
- General knee irritation from overuse or injury
Symptoms of a Baker's cyst
- A visible or palpable swelling at the back of the knee
- Tightness or stiffness behind the knee, particularly when bending or straightening fully
- Aching or discomfort in the popliteal area
- In larger cysts, limited range of motion
Occasionally, a Baker’s cyst can rupture — spilling fluid into the calf. This causes sudden pain and swelling in the calf that can mimic a deep vein thrombosis (DVT). If this occurs, it is important to seek urgent medical attention to exclude a DVT.
How is a Baker's cyst diagnosed?
Ultrasound is the most practical imaging tool for diagnosing and assessing a Baker’s cyst. It allows the clinician to visualise the cyst in real time, assess its size, and look for signs of the underlying knee pathology.
At Alton Pain Clinic, our consultant uses diagnostic ultrasound as part of the assessment, giving you a clear picture of what is happening in your knee.
Treatment for Baker's cyst
Treating the underlying cause
The most effective way to resolve a Baker’s cyst is to address the underlying knee problem that is causing excess fluid production. If osteoarthritis is driving the cyst, treatments targeting the joint — including cortisone or hyaluronic acid injections — will often reduce fluid production and allow the cyst to resolve.
Ultrasound-guided aspiration and steroid injection
For larger, symptomatic cysts, ultrasound-guided aspiration (draining the fluid with a needle) combined with a steroid injection is a very effective approach. The aspiration removes the cyst fluid immediately, and the steroid reduces inflammation and slows fluid re-accumulation.
At Alton Pain Clinic, this procedure is performed under real-time ultrasound guidance, which allows precise needle placement and improves safety and effectiveness.
How to sleep with a Baker's cyst
Night-time discomfort is a common complaint with Baker’s cysts. The following tips can help:
- Sleep with a pillow under your knee if you sleep on your back — this keeps the knee in slight flexion, which is usually the most comfortable position
- If you sleep on your side, place a pillow between your knees to reduce pressure
- Avoid sleeping with the knee fully extended, as this can increase tension behind the knee
- A cool compress before bed may help reduce discomfort
If night pain is severe or persistent, it is worth seeking treatment — ultrasound-guided aspiration can provide immediate relief and significantly improve sleep quality
This article is intended for informational purposes only and should not replace professional medical advice. If you are experiencing persistent symptoms, please consult a qualified clinician.
Frequently Asked Questions
Will a Baker's cyst go away on its own?
Small Baker’s cysts sometimes resolve spontaneously, particularly if the underlying cause settles down. Larger or persistent cysts are unlikely to disappear without treatment. Addressing the underlying knee problem is the most reliable way to achieve resolution.
Can a Baker's cyst be dangerous?
Baker’s cysts themselves are not dangerous, but a ruptured cyst can cause calf pain and swelling that resembles a DVT. It is important to seek urgent assessment if this occurs, to rule out a blood clot.
How long does it take for a Baker's cyst to go away after treatment?
After ultrasound-guided aspiration and steroid injection, the cyst often reduces significantly within a few days. Long-term resolution depends on whether the underlying knee problem is also addressed. If the knee continues to produce excess fluid, the cyst may recur.