Causes for Swollen Legs Post-Long Run

Hi Sports Doc!

I hope you can help me – I am triathlete training for my first ironman. I have been in endurance sports for 4 years. I am 42 years old. In the last year, anytime I run over 15 kilometres, I experience significant swelling in my right knee and leg.  The swelling centers in the knee joint, but is present in the thigh and ankle as well. Recently, I have been putting on surgical compression stockings after all my runs, which seems to help my recovery, but does little for the swelling. I have hyper-mobility in most of my joints and both my knees hyperextend when I am standing (unless I make a conscious effort to stand with them straight.) When the knee is swollen, I am unable to stand as I normally do and quad stretches are nearly impossible without feeling like the knee will burst. This typically wears off in about 2-3 days, but returns again after the next long run. My first marathon is in 12 days.

Of course most doctors I have talked to said, “MRI” and “STOP RUNNING” but this is difficult for me to justify to myself since I am having no pain. I am familiar with patellar tendonitis, as I have it in the left knee off and on, but this does not feel like that.

Any ideas?



Dear Windy,

Your leg is telling you something, and it is not saying, “run more!”

If you just had knee swelling, you would be describing an effusion of the knee joint, which is a reflection of joint irritation. Effusions are caused by irritation to the tissues that leak fluid into the joint and bursa spaces. You can lump effusions into trauma-related, like you see in football players, and non-trauma related; yours would seem fall into the non-trauma category. Common non-traumatic causes of effusion include infection, systemic rheumatic disease, infiltrative disorders, tumors, small meniscus cartilage tears, and osteoarthritis. Since the swelling is only running related, I would lean toward the osteoarthritis and/or a small meniscus tear. This might be helped by hyaluronic acid injections and would be something to discuss with your physician. Swelling in the knee can also be related to a knee injury from your high school or college days.

Your swelling seems to be more extensive than the knee and extends both above and below the joint, making me think that the venous outflow from your leg may be restricted to a point where you develop swelling in your whole leg, possibly in the groin area. When you push your mileage up, the resulting “backpressure” causes your entire leg to swell. This could be caused by something pressing on your large veins in the upper leg or pelvis, like a tumor, or a vein that is small naturally and unable to handle high flow of prolonged exercise. I have had one patient in my career with an absent left iliac vein who developed swelling with a very exhausting effort. An ultrasound before and after a long run may give you an answer as it can look at blood flow and detect any tissue mass that might be obstructing blood flow. You might need an MRI also to define the anatomic structures or joint fluid analysis to see if there is a cause like gout or some form of inflammatory arthritis.

You describe hypermobility of your joints and that is usually an inherited condition that does not cause problems for most people. Joint hypermobility can be the prominent feature of a rare medical condition called Ehlers-Danlos syndrome characterized by weakness of the connective tissues throughout the body. It would usually be diagnosed by your age, but you might ask your physician about it.

So that leaves us without an answer to your problem and you probably deserve an answer before your commit to longer distance runs that cause your symptoms. I think you should meet with your primary physician to have the problem fully evaluated. It will probably mean some blood tests and some other imaging that may include diagnostic ultrasound and MRI of your knee joint and possibly your pelvis. It could also mean that long duration leg activity like distance running is not possible for you.

I hope this helps.




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