What is a Baker cyst?

What is a Baker's Cyst?

A Baker's cyst is a fluid-filled sac that forms in the back of the knee, specifically between the gastrocnemius and semimembranosus muscles, often communicating with the knee joint space. 1, 2

Simple Explanation for Patients

• A Baker's cyst is a swelling that occurs at the back of your knee when fluid from your knee joint leaks into a small sac of tissue behind the knee 3
• It appears as a bulge or lump behind the knee that might feel like a water balloon 1
• These cysts are named after the surgeon who first described them, Dr. William Baker 3
• They are also sometimes called "popliteal cysts" because they form in the popliteal area (the back of the knee) 3

What Causes a Baker's Cyst?

• Baker's cysts typically develop when there's an underlying knee problem causing excess fluid production in the joint 3
• Common underlying conditions include:
  • Osteoarthritis of the knee 2
  • Meniscus tears 3
  • Rheumatoid arthritis 3
  • Other inflammatory conditions affecting the knee 3
• The excess fluid pushes through a one-way valve-like opening in the joint capsule, filling the bursa behind the knee 3

How to Recognize a Baker's Cyst

• You might notice a soft lump behind your knee that gets bigger when standing and smaller when lying down 1
• Common symptoms include:
  • Swelling behind the knee 3
  • Knee pain or discomfort 4
  • Stiffness or limited range of motion in the knee 4
  • Feeling of tightness behind the knee when bending or extending the leg 3
• In some cases, the cyst can rupture, causing pain and swelling that extends down into the calf 2

Types of Baker's Cysts

• Simple cysts: Contain only fluid with thin walls 5
• Complex cysts: Have both fluid and solid components, possibly with thick walls or septa 5, 1
• Complicated cysts: Have some features between simple and complex cysts 5

Diagnosis

• Your doctor can often diagnose a Baker's cyst through physical examination 3
• Ultrasound is commonly used to confirm the diagnosis and appears as a comma-shaped extension between specific muscles 1, 2
• MRI may be used for more detailed evaluation 3
• It's important to rule out other conditions that can mimic a Baker's cyst, such as deep vein thrombosis (blood clot) 1, 2

Treatment Options

• Many Baker's cysts don't require treatment if they're small and don't cause symptoms 2
• Treatment typically focuses on addressing the underlying knee condition 2
• Management options include:
  • Self-management education and activity modifications 2
  • Weight management for overweight patients 2
  • Physical therapy to strengthen surrounding muscles 2
  • Medications to reduce inflammation 6
  • Aspiration (draining the fluid) for symptomatic relief 5
  • In persistent cases with significant symptoms, surgical removal might be considered 4

Potential Complications

• Rupture of the cyst, causing pain and swelling in the calf 1
• The rupture can sometimes be mistaken for deep vein thrombosis 2
• Rarely, infection can occur 2

Remember that most Baker's cysts are not dangerous and often improve when the underlying knee condition is properly treated 2, 3.