Cracking, popping and clicking in the knee for some people can be a common occurrence. When you experience these noises, it is often reported that there is no associated pain or a loss of function or movement to the knee.
Whilst you may have been reassured and know these facts, when your joints behave in this way it often causes stress for a lot of people and is something that patients put a lot of focus on during their rehabilitation.
There is a common misconception that clicking or cracking in the joint is related to the development of osteoarthritis, that something is “out of place”, or that we are just “getting old” and will eventually need surgery. However, for most people it is not something to worry about and reassuringly there is scientific research supports why this phenomenon occurs.
The knee, like most of our major joints in the body, is a synovial joint. Synovial joints are surrounded by a joint capsule that contains synovial fluid, whose role it is to lubricate the joint and allow smooth movement. Over time gas bubbles build up inside the synovial fluid, and when we move our knee the pressure inside the joint changes. The popping or clicking that we hear is due to this change in pressure and the effect it has on the synovial fluid and creation of gas bubbles.
In 2015 Kawchuck et al. used MRI to provide evidence that knee cracking occurred due to formation of cavities within the knees. They further detailed that two surfaces of the knee resisted separation until a certain point, it is at that point when they separate quickly a gas cavity is formed. For most people these sounds often occur with innocuous activities such as running, squatting or bending, but are in fact completely harmless.
Clicking in the knee can also be associated with the patella (kneecap) locating itself within the groove of the femur (thighbone) and may feel or sound like a clunk. Ligaments and tendons can also pass over bony lumps and snap back into place, causing a loud snap. Again, these are usually painless and quite a normal occurrence in the general population.
In 2018 an article composed by Song et al. lists the numerous factors that can explain knee pain but emphasise that noise must be correlated with pathology..
The majority of people will only need to worry about your joints clicking or cracking is if those sounds are associated with pain, swelling, or a loss of function that affects your ability to perform your normal activities of daily living. In these instances, clicking may be the result of a damaged structure in your knee that may require treatment or further investigation, and you should consult your Physiotherapist for a full examination.
In the meantime, it is always important to remember to warm up appropriately before undertaking any activity. Pre-activating and getting blood flow to your working muscles are key factors in reducing acute knee injuries. Warm up drills such as high knees, bum kicks and lunges before any running stimulate blood flow to your legs so that they will have greater oxygen supply to perform the required task. It is also equally important to stretch after exercise but also as a normal part of your day. This will relieve tightness in the muscles that could limit movement and function and contribute to your knee clicking.
Written by Andrew Tran (Physiotherapist)
Kawchuk G.N., Fryer J., Jaremko J.L., Zeng H., Rowe L., & Thompson R. Real-time visualization of joint cavitation. PLoS One. 2015;10(4):e0119470