Fast facts

  • A Baker's cyst is a soft lump at the back of the knee. It is caused by synovial fluid building up inside a bursa.
  • A Baker's cyst can be caused by damage to the knee, including injury, infection or arthritis.
  • A Baker's cyst does not always require treatment, as the condition often goes away on its own. It is often recommended to wait and watch.
  • If treatments are needed, they can include physiotherapy, fluid draining, anti-inflammatory medication, and sometimes surgery.

Synovial

Pertaining to the fluid that lubricates joints (called synovia). A joint that produces synovia is referred to as a synovial joint.

What is a Baker's cyst?

A Baker's cyst, also known as a popliteal cyst, is an abnormal swelling that shows up as a soft lump at the back of the knee. Injury or disease can cause fluid to build up inside the bursa, a sac that reduces friction at a joint.

The fluid build-up can be painful and reduce movement at the joint. 

A Baker's cyst appears as a lump at the back of the knee. 

Signs and symptoms

A Baker's cyst might have no symptoms, but when symptoms do occur they may include:

  • A visible lump or swelling at the back of the knee;
  • Recurring pain in the knee;
  • A feeling of pressure in the back of the knee;
  • Reduced joint mobility, and;
  • A feeling of tightness in the knee when the leg is straightened.

Causes

Causes of Baker's cysts include:

  • Knee injury; 
  • Arthritis - rheumatoid arthritis and osteoarthritis of the knee;
  • Other types of damage to cartilage in the knee;
  • Infection in the knee, and;
  • Due to unknown causes.

Methods for diagnosis

To diagnose Baker's cyst, your doctor will examine your knee and ask questions about your medical history. They may also shine a light through the cyst to determine if it is fluid-filled. They may also ask for scans such as an X-ray, ultrasound or magnetic resonance imaging (MRI).

Magnetic resonance imaging

A type of imaging that uses a magnetic field and low-energy radio waves, instead of X-rays, to obtain images of organs.

Ultrasound

A scan that uses high-frequency soundwaves to produce images of the body’s internal structures.

X-ray

A scan that uses ionising radiation beams to create an image of the body’s internal structures.

Types of treatment

A Baker's cyst does not always require treatment, as the condition often goes away on its own. It is often recommended to wait and watch, especially for children.

If treatment is needed, it can include:

  • Physiotherapy: icepacks, crutches and special exercises to maintain and improve movement;
  • Draining fluid from the cyst with a needle. However, the cyst can return if there is an underlying condition that remains untreated;
  • Cortisone injections to reduce inflammation, and;
  • In some cases, surgery is performed to remove the cyst entirely.

Cortisone injections

Cortisone injections (also called steroids or corticosteroids) are the direct injection of corticosteroid hormones into a joint to relieve pain and inflammation. They are used for short-term relief from conditions such as arthritis, tendonitis and carpal tunnel syndrome.

Potential complications

Left untreated, complications of a Baker's cyst include:

  • Continued growth of the cyst and worsening of symptoms;
  • The growth of the cyst extending down the leg, and;
  • Bursting of the cyst, which causes sharp pain, swelling and redness in the leg.

Prognosis

Most people respond well to treatment and improve over time.

Prevention

Although you may not be able to prevent yourself from developing arthritis or getting an infection that causes a Baker's cyst, you can reduce your risk of injury by:

  • Taking time to warm up, cool down and stretch before and after sport and exercise;
  • Wearing supportive footwear, and;
  • Applying icepacks to the swollen area and seeking medical attention if you do hurt yourself.