Fact or Fiction: Cracking Your Knuckles Gives You Arthritis

If you are a knuckle cracker, like me, you’ve probably been told to stop cracking your knuckles as it can cause arthritis. But is there any truth to this claim, or is it something we’re told by people who don’t like the sound?

Cracking knuckles can feel good, but may bother those around you – Image Credit: Colin Davis, Flickr

To knuckle crackers, the audible ‘pop’ as knuckles are stretched and squeezed is the sound of relief and comfort. But to non-crackers, that ‘pop’ is often followed by a shudder of discomfort. In fact, that infamous popping sound is often associated with pain, so many people believe joint disorders will follow. As such, children are often told to stop cracking their knuckles.

 

Why Do Knuckles Crack?

The characteristic pop of a cracked knuckle is caused by tiny bubbles of gas.

In our bodies, synovial fluid helps to lubricate our joints. This fluid acts as a cushion to help our joints move smoothly.

When you crack your knuckles, you pull the joint apart, which reduces the pressure in the synovial fluid. The reduction in pressure allows bubbles to form. When the joint is returned to its normal size, the pressure increases again, and the bubbles pop.

 

Does Cracking Knuckles Cause Arthritis?

It would make sense for knuckle cracking to cause arthritis – repeated pushing and stretching of the joints can be painful and affect joint function. But to date, no studies have observed a connection between cracking knuckles and arthritis.

In fact, one scientist was so convinced that cracking knuckles would not lead to arthritis, he was willing to sacrifice his own hands for science.

Donald Unger cracked the knuckles in his left hand every day for 50 years. He did not crack his knuckles at all in his right hand. This way, he could directly compare how cracking his knuckles affected the health of his joints.

Unger found there was no difference in the health of his joints – neither hand had arthritis, or any joint issue. Unger won the Ig Nobel Prize in Medicine in 2009 for his work (the Ig Nobel Prize is awarded to research which “makes people laugh and then think”).

 

But even though cracking your knuckles won’t cause arthritis, there are still some negative side-effects.

Knuckle crackers have more swelling in their hands, and have a weaker grip compared to those who don’t crack their knuckles. This may be a result of the changing pressure in synovial fluid. Swelling may not cause pain, but it can be uncomfortable.

People who crack their knuckles may also injure themselves whilst they are cracking their knuckles: Pushing and stretching knuckles may lead to pain, swelling, immobility of the joint, and in extreme cases, dislocations.

 

So, although cracking you knuckles won’t give you arthritis, you may still want to consider giving up the habit.


8 Responses to “Fact or Fiction: Cracking Your Knuckles Gives You Arthritis”

  1. Debbie says:

    Hi Sarah,

    In this case, I think it was necessary for him to do it on himself – there’d be no way that kind of experiment would get ethics approval these days. But I agree totally, but you’d want to be absolutely certain before doing something like that!

    In regards to your knees, I can tell you that it is likely due to the synovial fluid. Knee cracks can be caused by a couple of reasons:
    The first and probably the most common is due to the gas bubbles in the synovial fluid.
    The second one is still perfectly normal, and comes from everyday wear and tear on your knees. It is caused by the tendons ‘snapping’ into place. Don’t be alarmed though, this snapping isn’t anywhere near as bad as it sounds, it’s simply the knee’s way of returning itself to it’s normal position.
    Both of these causes are very common (the second is quite common in athletes or those who exercise regularly) and both are completely normal. However, if your knees crack every time you stand up or bend them, it could be a sign that something more serious is going on. I’m not an expert, but some of these reasons could be due to your knee cap being misaligned (which in my case is due to a meniscus injury), early stage arthritis, or even the joint not being lubricated enough and rubbing together. If your circumstance is like this, I’d probably suggest getting your knees checked out by someone who has much more experience than me. However, in most cases, knee cracking is nothing to worry about.

  2. Debbie says:

    Hi Julian,
    I did try to source the origin of this myth, but as with many myths, it is quit difficult to trace. One potential source is that the joints of arthritis sufferers crack as part of their condition, so perhaps sufferers or those around them took this to meant the cracking sound was causing their arthritis. If this were the case, it would make sense to think that deliberately cracking your knuckles could cause arthritis. But now the causes of arthritis are better understood, the myth still gets circulated a lot, so there may be more to it than just this.

  3. Sarah Nielsen says:

    It’s always amusing when scientists decide to sacrifice themselves to prove others wrong! Dedication right there! I wonder if the same process occurs for other joints – my knees have a lot of fun cracking when they bend/straighten (much to the horror of those around me) – it would be interesting to find out if this is because of the same process of releasing the air bubbles within synovial fluid in the joint. It’s that or I just have really dreadful knees…

  4. Julian Carlin says:

    I find it interesting just how frequently the “cracking causes arthritis” myth gets passed around. There must be something about it that really appeals to those non-crackers out there! Maybe more than just as a justification for their annoyance at the sound?

  5. Debbie says:

    Hi Will,
    Thanks for the comment, and great question.
    The bubbles are microscopic – to give you an idea, the gas they are made of is usually dissolved in the synovial fluid, but the change of pressure causes it to accumulate. If you can stomach it, here is a link to an MRI scan of a knuckle cracking. If you look closely between the joint, you’ll see a slight discolouration, which is the bubble. When it pops, it disappears, which is the gas re-dissolving into the synovial fluid.
    https://www.youtube.com/watch?v=RKpLyB9LfwM
    Although the bubbles are quite small, the noise can be quite loud. This is due to a property of sound waves allowing them to travel further and faster: The spacing of molecules determines how fast/far noise can travel (http://www.learnnc.org/lp/editions/biomusic/6517). Sound travels about four times further and faster in water than it does in air, and it travels faster and further in synovial fluid than it does in water (because synovial fluid is more dense than water). This property means that the popping noise from the bubble bursting travels further (i.e. to our ears), and can travel quite quickly, meaning we can very clearly hear that distinctive pop.
    I hope this answers your question 🙂

  6. Will McDonald says:

    Hi,
    I was wondering how big these bubbles are?
    I imagine they must be pretty small, but then they make a decent amount of sound….

  7. Debbie says:

    Thanks Jasmin!
    You’ll find that many knuckle crackers experience the ‘less stiff’ knuckles after cracking them. This is because when you crack your knuckles, the knuckles momentarily become larger, allowing the joints to move more freely. So it isn’t that your knuckles are stiff if you don’t crack them, just that they feel less stiff when you do. This is probably why you no longer have this stiffness feeling, but if you were to go back to cracking your knuckles, you’d probably experience this feeling again.

  8. Jasmin says:

    Such a great read!

    I have been a long-time on/off knuckle cracker and always get people saying “ouch!” when I do it and telling me how bad it is for my hands. Although I have noticed that when I regularly crack my knuckles they feel stiff if I don’t crack them, so I’ve stopped because of this and now I find it harder to crack my knuckles again. I wonder why that happens?

    Anyway, I’m glad I probably won’t get arthritis from it!