A Baker’s cyst is a fluid-filled swelling that develops at the back of the knee. It occurs when excess synovial fluid, the lubricant for your joint, is pushed into a small sac (bursa) behind the knee. It is almost always a secondary symptom of an underlying knee issue, such as arthritis or a meniscus tear, rather than a standalone disease.
Small cysts may go unnoticed, but as they grow, they can cause significant mechanical discomfort.
Fullness in the Back of the Knee: A sensation of pressure or a visible bulge at the back of the joint, especially when standing.
Stiffness: Difficulty fully straightening or fully bending the knee (heel-to-buttock movement).
Pain with Activity: Discomfort that worsens when you are active or when the knee is fully extended.
Knee Locking or Catching: Since the cyst is often caused by a meniscus tear, you may experience mechanical snagging inside the joint.
Rupture Symptoms: If the cyst bursts, fluid leaks into the calf, causing sudden, sharp pain, redness, and swelling that can mimic a blood clot (DVT).
Because a Baker's cyst is a sign of an internal knee problem, diagnosis focuses on finding the underlying cause.
Physical Exam
Ultrasound: A quick, effective way to confirm the cyst is fluid-filled and to rule out a dangerous blood clot in the leg.
MRI: The gold standard for identifying the underlying cause, such as a meniscus injury or osteoarthritis, that is triggering the fluid overproduction.
Treating the cyst itself is usually temporary; the most effective approach is to treat the underlying joint problem.
RICE Protocol: Rest, Ice, Compression, and Elevation to reduce inflammation and fluid pressure.
Ultrasound Guided Aspiration: Using a needle to drain the fluid. This provides instant relief, but the cyst often refills if the internal knee issue isn't fixed.
Corticosteroid Injections: Injecting steroids into the joint to reduce inflammation and slow down fluid production.
Physical Therapy: Strengthening the muscles around the knee to reduce the load on the joint and improve fluid drainage.
Surgery: Treating the primary cause often causes the Baker's cyst to disappear on its own.