A blog by runners. For runners.

Why do my knees crack?

Runner Question:

My name is Sophia, I’m sixteen and I’m a high school runner. I started running at the beginning of last year, starting off with a few miles a week. I started running 3 miles everyday during the summer months of 2011, and in the fall I began cross country. We run 6 days a week, 5 miles a day. I’ve always noticed that my knee and foot joints crack. Is that normal for such a young girl? Is it just because of the running? Will it hurt my body in the future, and is there any way to prevent it?

Answer from Dr. Nace:

I get this question all the time from runners! In medical terms, we refer to this condition as crepitus, which simply means cracking or popping sounds and sensations in joints. There’s likely no cause for concern. This is completely normal for almost everyone, but especially runners to experience in their knees.

The knee has a balloon-like membrane around it filled with synovial fluid. Synovial fluid acts like gear oil for your joints and helps facilitate movement. The fluid lubricates the joint and helps your knee to bend and function properly so you can run and move around. Anytime you have pressure changes and movement inside a closed space, tiny air pockets develop. As you move around these air pockets tend to pop. The friction from movement and pressure changes create these bubbles and the popping is just your knee getting rid of the excess air in the synovial fluid.

Occasionally, you’ll notice more popping than usual or potentially a slight discomfort in joints. This can be due to changes in altitude or barometric pressure. If you go from high atmospheric pressure to low or low to high, your joints feel the change and it can result in more popping and cracking than normal. Barometric pressure fluctuates during changes in weather and during airplane flights due to the altitude change as you take off and land.

Generally, the popping or cracking of joints actually relieves discomfort and there is nothing to be worried about. However, if it is consistently painful before and after your knee cracks, it is best to get it checked out. There could be some loose cartilage or a loose body floating around in the synovial fluid surrounding your knee. If the cracking or popping doesn’t bother you and isn’t painful, then it is okay and you can carry on with your training. If it is still bothersome, schedule an appointment with a doctor and always remember to err on the side of caution. I hope this helps. Good luck with your training!

Related articles:

Written by Dr. James Nace, M.D.: James Nace, MD is an orthopedic surgeon-joint replacement and doctor of general orthopedics specializing in hip, knee and shoulder joint preservation and reconstruction. He practices out of the Rubin Institute for Advanced Orthopedics at Sinai Hospital of Baltimore, Maryland. Throughout his career as a physical therapist and orthopedic surgeon, Nace has gained the most satisfaction from treating runners and all types of athletes for their injuries and helping get them back to training and competing.