Harvard Men's Health Watch

On call: Baker's cyst

Q. I'm 67 years old, and except for an enlarged prostate, I'm in perfect health. Recently, I noticed a soft swelling behind my left knee. I saw an orthopedist who told me I have a Baker's cyst. He said I don't need any tests or treatments, but I worry that it may interfere with my tennis. Should I ignore it or get treatment?

A. Although the precise incidence is not known, Baker's cysts are quite common, particularly in people age 35 and up. These cysts are nothing more than an accumulation of fluid in one of the six bursa sacs that cushion the back of the knee. Because this part of the knee is known as the popliteal fossa, the fluid-filled sacs are also called popliteal cysts.

Popliteal cysts can develop following trauma or in association with torn knee cartilage, arthritis, or other knee problems — but they can also come on without rhyme or reason in otherwise healthy knees. Like yours, many are painless, but others cause aching or stiffness. If a cyst gets large enough to compress the calf vein, the calf and foot will swell up. If fluid leaks out of a cyst, the calf can be warm and tender, sometimes with a "black and blue" discoloration in the leg, ankle, or both.

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