Ask the Doc: Can I Run on a Swollen Knee If It Doesn’t Hurt?

A reader with an upcoming race wonders how to assess the seriousness of a potential injury.

Forum user MIrunguy asks: I think I tweaked my knee a couple days ago and it bothered me that night. Since then, there really hasn’t been any pain, but it’s still swollen. It feels like there’s some fluid buildup, and it is kind of tight. But the part that bothered me the other night was actually above and on the inside, while the swelling is below and on the outside. So maybe they aren’t related. 

I tried doing a 2km run today and while it felt a little tight, there was not really any pain. I have a 5K race tomorrow. Would it be stupid to still try and do it? Should I count my blessings it doesn’t hurt and just take it easy until the swelling goes down? Or if there is no pain, should I go for it?

I am not sure what you mean by “tweaked”, but it appears you incurred a non-contact injury while you were running. You have not stated your age, and age may play a role in the likely cause. The injury may be due to overuse, or it may be the result of a misstep, like an unexpected pothole.

Pain is a sign of tissue injury that is difficult to ignore. Other signs of tissue inflammation are warmth, redness, swelling and loss of function, and all indicate some tissue damage. The signs that do not cause pain or loss of function are sometimes easy to overlook, but all five of the inflammatory signs should be equally respected.

Swelling like you describe can be due to an injury that will heal with time, a connective tissue disease like rheumatoid arthritis, or degenerative arthritis. Degenerative arthritis can involve tears in the meniscus cartilage in the knee that could look or feel like a “tweak”, resulting in swelling without pain.

The knee is surrounded by synovial membrane that will fill with fluid when there is inflammation. The fluid collection is referred to as an effusion. The effusion should clear as the injury heals. The tightness you are feeling is from the swelling in the knee joint. What you need, if the swelling does not go away, is to see a doctor and get a diagnosis so you can make a reasonable decision regarding your return to running.

Running a 5K race with swelling in your knee has the potential to cause additional harm because your tissues are still inflamed. For your knee, it would be best to skip the racing and training until the swelling is gone.

In the long run, the regular running you are doing to race a 5K is more important for your health than the race itself. You may be able to participate in deep water running or other non-impact loading activities until the swelling resolves. If the swelling persists, you should see your physician and get to the root cause of your swelling.


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