Definition

A Baker’s cyst is a buildup of joint fluid behind the knee. It creates a tight bump behind your knee.

Causes

Joint fluid helps the knee move smoothly. A Baker’s cyst develops when there is too much of this fluid. The extra joint fluid is pushed out to the back of the knee. Extra fluid may be caused by:

• Arthritis — osteoarthritis is the most common type associated with Baker’s cysts
• Cartilage tears, such as a torn meniscus
• Injury or accidents
• Infection in joint

In children, Baker’s cyst may be related to a problem with the bursa. The bursa is a small fluid filled sac between the bone and soft tissue.

Risk Factors

Factors that may increase your chance of a Baker’s cyst include:

• Osteoarthritis
• Rheumatoid arthritis
• Infectious arthritis
• Gout
• Past knee injuries or cartilage tears
• History of corticosteroid injection around the knee
• Previous knee surgery
• Knee synovitis

Symptoms

A Baker’s cyst may cause:

• Rounded swelling behind the knee that may get bigger with activity
• Pain or pressure in the back of the knee joint—may travel to the calf muscle
• Aching or tenderness after exercise and bending the knee

Diagnosis

Your doctor will ask about your symptoms and medical history. A physical exam will be done. The doctor will look for a soft mass in the back of the knee. The range of motion in both knees will be tested and compared. The doctor may also shine a special light through the cyst. This will show that the cyst is filled with fluid and not solid.

Images of the knee occasionally needed to look for the cause and extent of the cyst . Images may be taken with:

• Ultrasound
• CT scan
• MRI scan

Blood tests may be taken if there may be an infection.

Treatment

Many Baker’s cysts resolve on their own without treatment. They usually go away within a two-year period.

The underlying cause may need treatment. This may include knee repairs or medication to treat medical conditions.

Treatment for the cyst itself may be needed if the cyst is painful or interferes with daily activities. Treatment options include:

• Medications to relieve pain and inflammation such as nonsteroidal anti-inflammatory drugs (NSAIDs)
• Physical therapy to help strengthen muscles around the knee
• Steroid injection
• Draining excess knee fluid
• Surgery—to remove large cysts or repair related knee injuries

Prevention

There are no current guidelines to prevent Baker’s cysts.

Sports Med—American Orthopaedic Society for Sports Medicine http://www.sportsmed.org/patient

Canadian Orthopaedic Foundation http://www.canorth.org/

Fritschy D, Fasel J, et al. The popliteal cyst. Knee Surg Sports Traumatol Arthrosc. 2006;14:623-628.

Popliteal cyst. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed
Updated November 15, 2011. Accessed January 4, 2013.

Torreggiani WC, Al-Ismael K, et al. The imaging spectrum of Baker’s (popliteal) cysts. Clin Radiol . 2002; 57:681-691.

Ward EE, Jacobson JA, et al. Sonographic detection of baker’s cysts: comparison with MR imaging. AJR Am J Roentgenol. 2001: 176:373-380.