Swollen Knee After Running? How to Treat and Prevent It

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A swollen knee is never normal and can warrant a trip to the doctor. But for the medical sleuths among you, here’s how to assess the situation—and prevent it from happening again.

If you get knee swelling after running, it may also be painful, stiff, and keep you from fully extending your leg. To figure out why it’s swollen, it’s important to identify when it first puffed up: immediately after or much later.

Swollen knee within an hour or two of activity: Swelling that occurs soon after an activity is much more serious than swelling that shows up, say, the next day. Example: You twist your knee trail running and it swells up. This is a sign of bleeding within the knee, or hemarthrosis. Basically, something has been torn or broken. About 80 percent of hemarthrosis cases are caused by a torn anterior cruciate ligament (ACL). Sudden-onset effusion is a sign that something serious is going on.

Swollen knee hours later or the day after activity: Swelling that arrives later is generally caused by excess synovial fluid (the lubricant in joints) in the knee, much like too much oil in a car. Overuse and an underlying medical condition are the most common causes. Something in there is irritated or rubbing during activity, and the body responds by over-lubricating the knee to compensate. Osteoarthritis is one of the most common causes, but far less common maladies can also be the culprits, such as rheumatoid arthritis, infection, gout, bursitis, cysts, bleeding disorders, tumors and Lyme disease. Advancing age and sports that require sudden changes in speed or direction raise your risk.

Fix Your Swollen Knee

See a doctor. Anytime you have a swollen joint, you should see a doctor. This is especially true with sudden-onset effusion

Employ dynamic rest. Even if the swelling comes without pain, avoid loading the knee until the swelling subsides. Trade knee-loading exercises for intense upper-body and core work.

Ice it. Apply ice to the swollen area for 15 minutes 4–6 times a day for the first two days. Elevating the knee as you ice it can also help reduce the swelling.

Prevent Your Knee From Swelling

Strengthen your legs. Strong legs protect your knees. Be sure your workout regimen includes regular lower-body strength training, in addition to any running and biking that you do. You may not be able to prevent knee effusion caused by health issues, but properly trained legs will help your knees recover in the long-run no matter what the issue turns out to be.

When to Call a Doctor

My philosophy is that any time you have joint swelling, you should see a doctor because you need to figure out what the problem is. Try to pinpoint when the effusion began in relation to your running or other athletic activities, especially if your knee has swelled up with no discernible cause, such as an overt injury, and you have no other symptoms that suggest a related illness. A physician can help shed light on the mystery, whether by physical exam, analysis of fluid drawn from the knee, or review of images such as MRIs or X-rays.

Also, if the knee is swollen but has some extra symptoms like redness or warmth of the skin and/or you have a fever, it could signal an infection. Get to an ER pronto.

Check out more common injury treatments and prevention techniques at the Med Tent