Baker's Cyst
A Baker’s cyst, or popliteal cyst, is a fluid-filled swelling that develops behind the knee, often due to arthritis or a knee injury. It can cause tightness, discomfort, or swelling, especially when the knee is bent or straightened. Understanding what causes it and how it’s treated can help you manage symptoms and stay active.
Overview | Symptoms & Causes | Diagnosis | Treatment Options
The Knee Joint
The knee is a large joint that connects the thigh bone (femur) to the shin bone (tibia), with the kneecap (patella) at the front. It’s supported by ligaments, tendons, and muscles that allow smooth movement and stability. The inside of the joint contains a small amount of fluid (synovial fluid) that keeps it lubricated.
If the knee becomes irritated or inflamed - for example, from arthritis or injury - extra fluid can build up and form a swelling at the back of the knee called a Baker’s cyst.
Understanding Baker's Cysts
A Baker’s cyst, also called a popliteal cyst, is a fluid-filled swelling that develops at the back of the knee. It often occurs when excess joint fluid (synovial fluid) is pushed into a small sac behind the knee, usually as a result of another knee problem such as arthritis, cartilage damage, or inflammation.
Many people with a Baker’s cyst notice a soft lump or bulge behind the knee that can vary in size. Common symptoms include:
- Tightness or stiffness at the back of the knee
- Swelling that may worsen when standing or being active
- Pain or discomfort, especially when bending or straightening the leg
- A feeling of pressure in the knee joint
Sometimes, the cyst may not cause any symptoms at all and is only found during a scan for another condition. If the cyst bursts, it can cause sudden pain, swelling, and redness in the calf, which can resemble a blood clot - in this case, medical attention is needed.
What causes a Baker's cyst?
Common causes:
- Arthritis: Conditions such as osteoarthritis or rheumatoid arthritis can inflame the knee and increase fluid production.
- Knee injuries: Tears in the cartilage (meniscus) or other joint damage can trigger fluid build-up.
- Overuse or repetitive strain: Activities that put repeated pressure on the knee may increase the risk of developing a cyst.
Risk factors:
- Existing knee problems or previous injuries: Issues such as meniscal tears, ligament injuries, or cartilage damage can lead to excess joint fluid, increasing the chance of a cyst.
- Older adults: Wear and tear becomes more common with age, making conditions like osteoarthritis more likely and raising the risk of a cyst.
- Inflammatory conditions: Rheumatoid arthritis, gout, or other inflammatory joint diseases can cause swelling inside the knee, which can lead to a Baker’s cyst.
Diagnosing a Baker's Cyst
Baker’s cysts are usually diagnosed through a combination of medical history, physical examination, and imaging tests. Your doctor will examine the back of your knee for swelling or a visible lump and ask about any pain, stiffness, or changes in movement. Early diagnosis is helpful for managing symptoms and addressing any underlying knee problems that might be causing the cyst.
To confirm the diagnosis and check for underlying knee problems, your doctor may recommend:
| Ultrasound | A painless scan that uses sound waves, which can show fluid-filled sacs and help distinguish a cyst from other types of lumps. |
| MRI | Provides a detailed view of the knee’s soft tissues, including cartilage, ligaments, and any inflammation that may be causing the cyst. |
| X-Ray | While they cannot show the cyst itself, they can help detect arthritis or other changes in the joint that may be contributing to fluid build-up. |
Treatment Options
Most Baker’s cysts improve on their own or with treatment of the underlying knee problem. The aim is to relieve discomfort, reduce swelling, and prevent the cyst from recurring.
Conservative Treatments
- Rest and activity modification: Avoiding activities that put repeated pressure on the knee can reduce swelling and pain.
- Pain relief: Over-the-counter painkillers or anti-inflammatory medicines can help ease discomfort.
- Ice and elevation: Applying ice to the back of the knee and elevating the leg may reduce swelling.
- Physiotherapy: Exercises to strengthen the muscles around the knee and improve joint movement can help manage symptoms and prevent recurrence.
Procedural Options
| Aspiration | Fluid can be drained from the cyst in some cases, though cysts often return if the underlying problem isn’t treated. |
| Steroid injections | Reduce inflammation and help relieve pain in the knee joint, which may also reduce cyst size. |
| Surgery | Rarely needed, but may be considered if the cyst is very large, painful, or causing complications, usually alongside repair of any underlying knee issue. |
How can Lanthorn help?
Knee Ultrasound - £300
An ultrasound scan provides a quick, detailed look at the structures behind the knee. It can confirm the presence of a Baker’s cyst, assess its size, and check for related issues such as fluid build-up or soft tissue problems.
Ultrasound-guided aspiration - £450
If needed, a Baker’s cyst can be drained (aspirated) to relieve pressure and discomfort. A steroid injection may then be given to reduce inflammation and decrease the likelihood of the cyst returning. Using ultrasound guidance ensures the procedure is precise and safe.
Knee MRI - £350
MRI offers a more comprehensive view of the knee joint, helping to identify underlying causes like meniscal tears, cartilage damage, or arthritis. This is especially useful when symptoms are persistent or when planning treatment.
