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If underlying conditions such as osteoarthritis are treated, you will have a much better chance of avoiding a Baker's cyst.

A Baker's cyst is a cyst (fluid-filled sac) that forms on the back of the knee. Baker's cysts are usually not very painful, but can be uncomfortable and give a sense of fullness and tightness at the back of the knee. They are cysts that have become filled with thickened joint fluid that has typically leaked out from the knee joint.

Causes
A Baker's cyst forms when synovial (joint) fluid, which is normally inside the knee joint, leaks out of the joint space into the back of the upper leg. This fluid forms a sac that can be felt on the back of the knee. Baker's cysts are caused by inflammation in the knee that causes swelling within the joint. The swelling in the knee increases the pressure within the knee joint and causes the joint fluid to leak out of the joint space. Baker's cysts in adults are typically the result of an injury or condition within the knee, such as a meniscus cartilage tear or osteoarthritis. Baker's cysts can also appear in children, most commonly between the ages of 4 and 7. Baker's cysts in children normally disappear as the child matures but should be examined by a doctor.

Symptoms
A Baker's cyst can feel like a small lump under the skin on the back of the knee. The cyst may feel uncomfortable and may cause stiffness in the knee, and may become more swollen and painful if the knee is bent repeatedly.

Risk Factors
The most common factors that can contribute to a Baker's cyst are conditions that cause swelling within the knee, such as a meniscus cartilage tear or osteoarthritis.

Diagnosis
Your doctor can diagnose a Baker's cyst by examining your knee and learning more about the history of the swelling. X-rays may be taken to determine what underlying conditions within the knee may be contributing to the cyst. Magnetic resonance imaging (MRI) examination may be used to visualize the injured knee joint structures that may be causing the inflammation and the Baker's cyst.

Treatment
Most Baker's cysts will disappear on their own, without treatment, if the underlying inflammation within the knee joint dissipates.

Treatments that may also prove helpful include:

  • Rest . All activities that cause pain and inflammation in the knee joint should be restricted. Talk with your doctor about a plan for gradually returning to full activity.
  • Ice . Ice packs may be used for about 20 minutes at a time, each hour to help alleviate pain and decrease swelling.
  • Bandage/Compression Wraps . Your doctor may recommend that you use a soft elastic wrap or bandage at the knee to help reduce swelling.
  • Elevation . Elevating the knee should help ease pain and swelling. Ideally, the foot should be elevated higher than the knee, and the knee should be elevated higher than the hip.
  • Medication . Your doctor may prescribe an anti-inflammatory medication.

In more severe cases, your doctor may use a needle to drain the fluid in the cyst to help ease the pressure and pain. This may be only a temporary solution as the cyst may refill with fluid if the underlying inflammation within the knee joint persists. If a Baker's cyst persists and is associated with an underlying condition of the knee, such as a meniscus cartilage tear or osteoarthritis, surgery may be recommended to correct the underlying condition within the knee, which will help to resolve the cyst.