Knee Crepitus – Should You Be Worried?

Do you hear a crunching, cracking or rubbing noise in your knee (also called knee crepitus)? Then you’ve probably wondered where these sounds come from and whether you should be worried about them. Don’t worry, in this article I will explain everything you need to know and show you how to deal with it.

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How do joint noises like cracking or grinding in the knee occur?

First of all, it should be said that not all joint noises are the same. There are many different types, which in the literature are usually summarized under the term “crepitus.” However, I will differentiate a bit between cracking, grinding, and snapping throughout the article.

Before I explain how joint noises occur in the first place, I find it interesting to look at what people think causes these noises.

There is a nice study by Demoulin et al. (2018). Their investigation of the spine is, of course, not directly transferable to other joints, but just to give you an idea:

  • About 50% of the participants attributed the joint noises during spinal manipulation to a displacement of the vertebrae.
  • About 25% of the participants believed that the noises were caused by friction between two vertebrae.

Let’s take a look at cracking as a classic joint noise. This occurs due to a sudden movement. This sudden movement creates a kind of vacuum or negative pressure in the joint. As a result, small air bubbles can form. This cracking noise is produced by the formation of these air bubbles, not even when they burst, but when they form.

Grinding in the knee joint usually occurs due to friction. Examples include the rubbing of two bones against each other, as in osteoarthritis, or friction on the cartilage or meniscus, which causes grinding in the knee.

Additionally, there are things like the plica. This is a fold that goes around the joint.

Knee crepitus - Plica
Illustration of the plica with fold (circled in red)

In the plica, a little fold can form that may protrude into the knee joint. This can also cause friction, which then triggers a crunching noise in the knee.

Then there’s also snapping. This usually happens when a ligament or tendon rubs over a bony prominence and then snaps back into place. Of course, there are more joint noises, but I would stick to these three types for now.

Should you be worried about knee crepitus?

First of all, we need to categorize them into two groups.

We have the physiological joint noises, which are basically normal and painless, and the pathological joint noises, which cause problems.

Physiological joint noises in the knee joint. These include the cracking I mentioned earlier, which occurs due to a sudden movement. The crunching in the knee, e.g., at the plica, a slightly altered meniscus, or a hypermobile meniscus. As well as snapping noises caused by ligaments and tendons. All of these noises are completely normal and harmless.

A fourth category of physiological joint noises are those that arise after surgery. Interestingly, the joint noises were usually already there, but the surgery shifts focus to the respective joint, e.g., the knee. Suddenly, people notice the noises. These noises have no negative meaning because they were always there, but now the focus is on them. That’s why many people worry even though they shouldn’t.

Pathological joint noises (arthrosis, knee pain…). These arise, among other things, due to degenerative processes in the joint. A classic example is arthrosis, where cartilage damage occurs. Otherwise, severe meniscal injuries also lead to pathological joint noises. Another common point is excessive mobility of the kneecap due to instability. This excessive mobility of the kneecap also leads to something like crunching in the knee.

There are also pathological changes in the plica. You might have heard of plica syndrome. It can also cause joint noises. Lastly, there are pathological joint noises that arise after surgery. This is not uncommon either. These noises occur when joint guidance is no longer the same as before or other structures now rub against each other in a way that produces a noise.

Is the joint noise physiological or pathological? The simplest indicator here is to watch out for swelling and pain. If the joint noise is accompanied by knee pain and/or swelling, it is likely pathological and should be examined by an orthopedist. If you have no pain or swelling at all, it is most likely physiological and you don’t need to worry.

Moreover, it is often clear what triggers pathological joint noises. Suppose you had surgery, a meniscus tear, or something similar. If the joint noises only started afterward, you can fairly clearly attribute them to this trigger.

Another helpful tip is to see if the noises are reproducible—if you can consistently trigger them with the same load or movement, or if they are very variable. If the joint noise is very variable, it is most likely completely harmless. If you can consistently trigger it with the same movement, it is probably pathological.

There are also tests like placing your hand on your knee and then extending and bending your leg. However, looking at studies on this, these tests do not fare well.

If you want to be very precise, there are now very objective measuring methods like vibration devices or air microphones that can accurately measure the noise. These can then identify connections with arthrosis. If the noise is louder, lasts longer, and has a higher frequency, it indicates a pathological joint noise. However, these objective measuring methods are not widely available and are relatively error-prone due to vibrations and external noises.

How should you deal with it?

With physiological joint noises, you’ve done what you need to. The most important thing here is to understand that these joint noises are not problematic. So you can just go about your business.

With pathological joint noises, it depends on what causes the noise. With arthrosis, reducing inflammation and strengthening surrounding structures like the muscles around the knee joint play a big role. If you have a pathological plica, conservative therapy with exercises is usually tried first. If that doesn’t help, it can also be surgically removed.

With kneecap instability, again, the method of choice is to start conservatively and particularly work on strengthening exercises for the front thigh muscles. Only if this doesn’t help at all do surgical procedures come into play.

For noises caused by meniscus injuries, one should assess how severe the meniscus injury is. Depending on this assessment, one must weigh whether surgical intervention is needed to stop these noises or if they will resolve on their own over time.

Lastly, for joint noises that occur after surgery: It’s been found that especially people with very high expectations from surgery are often dissatisfied afterward and severely restrict themselves when joint noises occur. Therefore, it’s extremely important to inform yourself that joint noises can occur post-surgery. You’ve already done this now.

Or if you’re working as a service provider, it’s crucial to inform patients that post-surgery joint noises are very common and don’t automatically mean something bad has happened.

If this education about joint noises has taken place, but they still occur and might be pathological, then one must look more closely. Was it due to the surgical procedure, rehabilitation, or other reasons that these noises have now arisen post-surgery? I can’t give you a clear recommendation on this now.


  • Demoulin, C., Baeri, D., Toussaint, G., Cagnie, B., Beernaert, A., Kaux, J. F., & Vanderthommen, M. (2018). Beliefs in the population about cracking sounds produced during spinal manipulation. Joint bone spine85(2), 239–242.
  • De Oliveira Silva, D., Pazzinatto, M. F., Priore, L. B. D., Ferreira, A. S., Briani, R. V., Ferrari, D., Bazett-Jones, D., & Azevedo, F. M. (2018). Knee crepitus is prevalent in women with patellofemoral pain, but is not related with function, physical activity and pain. Physical therapy in sport : official journal of the Association of Chartered Physiotherapists in Sports Medicine33, 7–11. 
  • Kawchuk, G. N., Fryer, J., Jaremko, J. L., Zeng, H., Rowe, L., & Thompson, R. (2015). Real-time visualization of joint cavitation. PloS one10(4), e0119470. 
  • McCoy, G. F., McCrea, J. D., Beverland, D. E., Kernohan, W. G., & Mollan, R. A. (1987). Vibration arthrography as a diagnostic aid in diseases of the knee. A preliminary report. The Journal of bone and joint surgery. British volume69(2), 288–293.
  • Robertson, C. J., Hurley, M., & Jones, F. (2017). People’s beliefs about the meaning of crepitus in patellofemoral pain and the impact of these beliefs on their behaviour: A qualitative study. Musculoskeletal science & practice28, 59–64.
  • Song, S. J., Park, C. H., Liang, H., & Kim, S. J. (2018). Noise around the Knee. Clinics in orthopedic surgery10(1), 1–8.

Gino Lazzaro

Gino has a Master's degree in sports physiotherapy. In his company Perform Perfect, he offers highly individualized 1:1 Pain Coaching for athletes who have been dealing with pain for more than three months.

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