Is the lump behind my knee a cyst?

Dear Alice,

I have a one half inch lump inside the back of my leg two inches above my knee (there is no visible mark on the skin). It is not painful or bothersome in any way. An acupuncturist thinks it is a cyst. If it is, what kind might it be, what kind of treatment might I get, and how necessary is it?

Dear Reader, 

Kudos to you for tuning into the lumps and bumps on your body. Often, these changes are indications of an underlying health concern that’s best addressed in a medical visit. Based on the description you’ve provided, the lump may be what’s referred to as popliteal cyst or Baker’s cyst (named after the physician who discovered it). These fluid-filled sacs are sometimes painful, may cause swelling behind the knee, or lead to knee pain or stiffness. These symptoms can usually be managed, but talking with a health care provider about any pain or discomfort is a good step towards getting it treated. Additionally, they’re the only ones who can make a diagnosis about what may be causing the lump to form. 

More about cysts: They're sacs that are filled with fluid, solid substances, or even air. They can occur in any tissue of the body, but the most obvious cysts are those that occur in the skin. The Baker’s cyst occurs when the fluid that helps lubricate the knee joint bulges out from between the bones. While it’s sometimes related to arthritis or other conditions causing inflammation to the knees, the cyst itself is usually painless and harmless. It’s also worth mentioning that there could be other reasons for the bump.

Diagnosing a cyst can be done with a physical exam. Your health care provider may ask you about any growths and changes that you might have noticed and will examine the cyst for tenderness and size. They may also choose to do an imaging test, such as an X-ray or ultrasound, to make sure the bump isn’t due to another health concern. 

Most cysts don’t require treatment as they aren’t painful. If you do experience some discomfort, you can use strategies to reduce some of the inflammation. These include R.I.C.E. (rest, ice, compression, and elevation), over-the-counter pain relievers, or by reducing the amount of physical activity. If the cyst does start to become painful, it can be treated with medication, fluid drainage using needle aspiration, or physical therapy. If the cyst gets worse or you experience a sharp pain in your knee, swelling or redness in the calf, or a feeling of water running down your calf, it's good to seek medical support as soon as possible, as it could be a sign that the cyst has burst, but this is a rare occurrence. 

It’s great that you’re in tune with your body  you’re the first line of defense for noticing anything new and different. Keep up the good detective work. 

Last updated Oct 23, 2020
Originally published Sep 26, 2003

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