KNEE CYST!
Watch this explanation of knee cysts.
A knee cyst is a fluid‑filled swelling that can develop in or around the knee joint. The most common type is the Baker’s cyst (also called a popliteal cyst), which forms behind the knee. While many knee cysts are harmless, they can cause discomfort, limit movement, and sometimes signal an underlying joint problem.
In this guide, we’ll explain the different types of knee cysts, their causes, symptoms, and treatment options — plus when to see a doctor.
What Is a Knee Cyst?
A knee cyst is a sac filled with synovial fluid — the lubricating fluid inside your joints. This fluid can leak or collect in certain areas due to injury, inflammation, or degenerative changes in the knee.
- Baker’s cyst (popliteal cyst) – swelling at the back of the knee, often linked to arthritis or meniscus tears.
- Meniscal cyst – forms along the joint line, usually due to a meniscus tear.
- Ganglion cyst – can develop within ligaments or tendons around the knee.
- Proximal tibiofibular joint cyst – rare, near the top of the shinbone.
Causes of Knee Cysts
[Image 2: Diagram showing knee joint anatomy with inflamed area]
Knee cysts often develop as a result of:
- Arthritis (osteoarthritis or rheumatoid arthritis)
- Meniscus tears or cartilage damage
- Ligament injuries
- Overuse or repetitive strain
- Inflammatory joint conditions (like gout or pseudogout)
When the knee produces excess synovial fluid due to irritation or injury, the fluid can collect in a pouch, forming a cyst.
Symptoms of a Knee Cyst
Some cysts cause no symptoms and are found during routine exams. When symptoms occur, they may include:
- Swelling or a lump (often behind the knee)
- Knee pain or aching
- Stiffness or reduced range of motion
- A feeling of tightness, especially when bending or straightening the knee
- In rare cases, redness and warmth if the cyst ruptures
In addition, a ruptured cyst can cause sudden pain and swelling in the calf, which can mimic a blood clot — seek medical attention immediately if this happens.
Diagnosis
Doctors may use:
- Physical examination – feeling for lumps or swelling
- Ultrasound – to confirm fluid‑filled nature
- MRI – to check for underlying joint damage
- X‑ray – to rule out bone problems