When Should You See a Doctor for a Baker’s Cyst?

Baker's cysts are fluid-filled sacs that form behind the knee. Baker's cysts are often harmless, but you should see a doctor if it is painful because it may indicate a more serious problem like an infection or a blood clot.

Cysts are small, fluid-filled sacs that can appear anywhere on your body. These growths are called a Baker’s cyst when they form on the back of your leg behind your knee. Other names for this kind of cyst include popliteal cyst and popliteal synovial cyst.

Baker’s cysts are relatively harmless and most often go away on their own. However, painful swelling behind the knee may indicate a more serious problem such as an infection or a blood clot. This is why it’s important to see a doctor when this occurs.

Your knee joint is filled with a slippery liquid known as synovial fluid that cushions the joint where the bones in your leg — the femur (thighbone) and tibia (shinbone) — meet. Baker’s cysts are the result of swelling in the knee due to an increase in this fluid. A buildup of pressure can squeeze fluid back into the knee, causing a Baker’s cyst.

Many times you won’t even know you have a Baker’s cyst because it doesn’t always cause pain or discomfort. However, you may notice symptoms such as:

Swelling

Swelling behind your knee that persists after an injury heals may be the only sign that you have a Baker’s cyst. However, a Baker’s cyst may cause stiffness or discomfort, with or without painful swelling.

Pressure

A feeling like you have a water-filled balloon behind your leg may indicate a cyst. If a cyst ruptures, it can cause swelling, bruising, and pain on the back of the knee.

Decreased range of motion

In addition, you may experience a decrease in your range of motion or the feeling that your knee catches or locks when you walk or bend.

When you injure your knee, swelling usually occurs as your body’s response to protecting the affected area. However, when too much synovial fluid releases into your knee, it causes pressure, leading to the extra fluid draining into the space behind your knee.

Baker’s cysts commonly occur when you have:

• A tear in the meniscal cartilage of your knee
• Other cartilage injuries
• Arthritis in your knees
• Rheumatoid arthritis
• Other knee problems

Swelling that comes on quickly or doesn’t go away may be a sign of infection. Other signs of infection include fever, tiredness, and severe knee pain. You should also call your doctor if you experience shortness of breath along with swelling in your leg.

Pain and/or swelling behind the knee might also be a sign of a blood clot, which is a much more dangerous condition that should be addressed immediately. 

Your doctor will perform a physical exam and ask about the symptoms you’re experiencing, which will most likely be related to an injury that occurred to your knee. Because just one knee is affected most of the time, your doctor will compare the affected knee with the other one to assess swelling. 

Your doctor can also shine a light on the cyst to see if the fluid appears to light up, as it is translucent under the skin. 

While X-rays will not show the presence of a cyst, they will show evidence of the damage that caused your cyst. Your doctor may request an MRI (magnetic resonance imaging) scan to see the cyst itself as well as look for any tearing that may have caused the cyst.

A Baker's cyst usually resolves by itself. If your cyst does not go away on its own, or if it is causing you pain, your doctor can drain the fluid with a needle (a procedure known as arthrocentesis). 

Other treatments for Baker’s cysts include:

• Over-the-counter (OTC) medications
• Steroid injections in the knee joint
• Surgery that removes the cyst

If an injury or other medical condition like arthritis is causing your Baker's cyst, that problem will need treatment. Otherwise, your cyst may continue to return, potentially causing more damage. 

Home treatment

There are steps you can take at home to help your cyst heal. These include: 

• Applying a compression wrap or a cold pack
• Using a cane or crutch to reduce pressure on your joint while walking
• Propping up your knee and resting it as much as you can
• Taking OTC anti-inflammatory medications such as ibuprofen

Physical therapy

Physical therapy can help if the cyst affects your range of motion or you have permanent damage from an injury. When you have an injury, you may overcompensate by walking or carrying yourself differently. A physical therapist can help you stretch and relearn how to use your knee as the cyst heals.

Surgery

If your injury is bad enough, your doctor may refer you for surgery to repair the damage. By fixing the problem that caused your cyst, future damage can be prevented.