Elite Facilities. Superior Care

Why do knees crack?

With the Melbourne Marathon only a week or so away, there are lots of runners out there frantically trying to prepare for the race. It’s a gruelling 42Km that undoubtedly will test both your mental and physical fortitude. Leading up to the race, many runners will be sore, and many more will have to deal with nagging injuries. Hopefully everyone has been managing them well and is ready to go at that start line next weekend. With all this in mind, I’d like to look at a very common question we hear and have to answer in the clinic…


Firstly, let us look at the anatomy. With regards to other joints in our body, the knee is relatively simple and is comprised of two different articulating surfaces: (i) tibiofemoral joint, and (ii) patellofemoral joint. These two joints create a hinge like structure that allows us to bend and straighten our knee as well as provide a mechanical advantage for our muscles to create strength and power. Other structures around the knee include; muscles, ligaments, tendons, menisci, synovial fluid, bursa, and a fat pad.

There are many reasons behind why our joints make noises when we move. The majority of the time these audible sounds are completely normal and are not indicative of detrimental pathology or disease. Firstly, when our knee goes through its full range of motion, from bending to straightening and vice versa, the muscles and tendons go through a stretch and shorten cycle. As this takes place, you can both hear and feel a popping or snapping sensation. This is caused by the tendon being flicked over a bony prominence. Very similar to the sensation of clicking your fingers. The noise actually comes from when the middle finger hits up against the pad on the base of your thumb. Secondly, as the knee joint moves, the sudden separation of the bones involved creates a vacuum-like scenario. This results in an area of negative pressure which subsequently draws in synovial fluid. It is the influx of this fluid into the new cavity created through movement that gives off the sensation and audible popping noise.

Different to the larger popping and snapping sounds as described above, our joints can also create noises such as fine grating crepitations. These sounds are manifested as fluid flows through our joints. This is commonly seen and heard in the patellofemoral joint as the synovial fluid flows through the slightly rougher retropatellar surface. In short, healthy joints that have appropriate mobility and are well lubricated make noise. Debunking the myth that cracking/popping/snapping joints automatically mean degeneration is very important for us as health professionals. Eliminating such negative health beliefs is a step in the right direction with regards to positive health outcomes.

Of course, if any of the above symptoms are associated with pain then an appropriate health examination and assessment by a qualified physiotherapist should be warranted. Come see us here at Recover Sports Medicine if you or anyone you know is concerned about your knee or any other joint in your body. We are always ready and willing to help in any manner possible.

Mike Killip
Recover Sports Medicine

If you would like to make an appointment with our Physiotherapist, please call 1300 858 774 or CLICK HERE to book online

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