BAKER'S CYST
What is Baker's Cyst?
A Baker’s cyst, also known as a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee. It often causes a noticeable lump and a feeling of tightness, which can be uncomfortable, particularly when bending or fully straightening the knee.
A Baker cyst of the knee joint typically arises from an underlying problem within the joint itself — such as osteoarthritis, rheumatoid arthritis, or a cartilage (meniscus) tear — that causes the knee to produce excess synovial fluid. This surplus fluid is pushed backwards into the popliteal bursa, a small fluid-filled sac behind the knee, causing it to swell. Because the cyst originates from the joint rather than the surrounding soft tissue, addressing the underlying joint condition is usually central to resolving it.
Symptoms of a Baker's Cyst
The main symptom is a noticeable lump at the back of the knee. Other common signs include:
- Pain in the knee, particularly when fully bending or straightening the leg
- Stiffness and difficulty moving the knee
- Swelling around the knee or upper calf
- A feeling of tightness behind the knee, especially after standing or activity
Some people have no symptoms at all and only discover the cyst incidentally during examination for another knee-related issue.
It’s worth noting that swelling and discolouration in the calf can sometimes mimic the signs of a blood clot (DVT). As blood clots are a medical emergency, anyone experiencing these symptoms should seek immediate medical advice to rule this out.
Baker's Cyst Treatment at Alton Pain Clinic
At Alton Pain Clinic, we provide ultrasound-guided cortisone injection and aspiration to relieve the swelling and discomfort associated with a Baker’s cyst.
Aspiration
Aspiration involves draining the excess fluid directly from the cyst using a fine needle, guided in real time by ultrasound. This reduces the size of the swelling and eases the associated tightness and discomfort.
Ultrasound-Guided Cortisone Injection
Cortisone is a corticosteroid that helps to calm inflammation within the joint and surrounding tissue. Delivered under ultrasound guidance, the injection is placed precisely at the site of inflammation, helping to:
- Reduce swelling and pressure within the cyst
- Limit further excess synovial fluid production
- Ease pressure on surrounding tendons and muscles, improving comfort and function
Combining aspiration with a cortisone injection in the same appointment allows both immediate fluid drainage and longer-term inflammation control, using real-time ultrasound imaging throughout to maximise accuracy and minimise discomfort.
What Causes a Baker's Cyst?
A number of underlying knee conditions can lead to the excess fluid production that forms a Baker’s cyst, including:
- Osteoarthritis — gradual wear and tear of the knee joint
- Rheumatoid arthritis — a chronic inflammatory autoimmune condition
- Meniscal (cartilage) tears — often from injury or twisting movements
- Gout — a build-up of uric acid crystals within the joint
- Septic arthritis — infection within the joint
- Injury or trauma to the knee, particularly in athletes
In each case, irritation or inflammation within the knee joint prompts an increase in synovial fluid production, which can then collect behind the knee to form the cyst.
Your Care Pathway with us
- To book an appointment you can call our reception line, 0142084487, or email to info@altonpainclinic.co.uk or click the button given below.
- Comprehensive Musculoskeletal examination and testing.
- Same day Ultrasound Guided Injection for pain relief.
- Discussion of your treatment plan, treatment plan can include advanced treatments for example Cortisone Injections, Hyaluronic injections and various other options tailored to your specific needs.
What our Patients say?
Anatomy of a Baker's Cyst
A Baker’s cyst develops in the popliteal space, which is the hollow region at the back of the knee. The main structures involved in the formation of a Baker’s cyst include:
- Popliteal Bursa: A small fluid-filled sac located at the back of the knee. It cushions the knee joint and helps reduce friction between muscles, tendons, and bones.
- Synovial Fluid: A thick, lubricating fluid that keeps the knee joint moving smoothly and reduces wear on the cartilage and tissues within the joint. This fluid circulates through the bursae in the knee.
- Valve-Like Mechanism: There’s a valve system between the knee joint and the popliteal bursa, controlling the flow of synovial fluid. This valve maintains a balanced flow of fluid into and out of the bursa when functioning correctly.
When the knee joint faces an underlying issue like arthritis or an injury, it can produce excess synovial fluid. This surplus of fluid accumulates in the popliteal bursa, causing it to swell and form a Baker’s cyst. In some cases, the cyst may extend downward into the calf.
How Is a Baker's Cyst Diagnosed?
A clinician will usually diagnose a Baker’s cyst through a physical examination, checking for a lump behind the knee and asking when it first appeared and whether other symptoms are present. If the cyst developed following an injury, describing how it happened can help guide diagnosis.
Imaging may be used to confirm the diagnosis and assess the underlying joint, including:
- Ultrasound — our preferred method, allowing real-time assessment of the cyst and surrounding structures
- X-ray or MRI (We do not perform X-rays or MRI scans at our clinic. If imaging is required, we may recommend that you arrange an X-ray or MRI scan separately.)
Key Takeaways
A Baker’s cyst is a fluid-filled swelling behind the knee, usually caused by an underlying knee joint problem. It develops when excess synovial fluid is pushed into the popliteal bursa, so treating the underlying cause is key to achieving lasting relief. At Alton Pain Clinic, we provide ultrasound-guided cortisone injections and aspiration to help relieve swelling and discomfort. Most patients notice a reduction in swelling within days of treatment, although how long a Baker’s cyst lasts without treatment varies depending on its underlying cause. If a Baker’s cyst bursts, seek prompt medical attention, as its symptoms can sometimes mimic those of a blood clot.
Frequently Asked Questions
What is the most common cause of a Baker's cyst?
Excess fluid in the knee joint due to inflammation, most often from osteoarthritis or a meniscal tear.
How long does a Baker's cyst last?
Small, uncomplicated cysts can settle within a few weeks once the underlying knee irritation is addressed. Larger cysts linked to arthritis or a meniscus tear may persist for months without treatment. With ultrasound-guided aspiration and cortisone injection at Alton Pain Clinic, most patients notice a reduction in swelling within days, although the cyst can recur if the underlying joint condition isn’t managed. It varies from person to person.
What happens if a Baker's cyst bursts?
If a Baker’s cyst bursts, fluid can leak into the calf, causing sudden pain, swelling and sometimes bruising that may resemble the signs of a blood clot (DVT). As this is considered a medical emergency, prompt medical attention should be sought to rule out a clot.
How is a Baker's cyst removed?
Most cysts don’t require surgical removal. First-line treatment at Alton Pain Clinic is ultrasound-guided aspiration, often combined with a cortisone injection to reduce inflammation and lower the chance of the cyst refilling.
Can a Baker's cyst occur without arthritis?
Yes. While arthritis is a common cause, knee injuries such as a meniscus tear can also trigger fluid accumulation and cyst formation on their own.