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I pop my knuckles fairly frequently, and I have been told on several occasions that doing so is bad for your joints. Is this true? Have there been any medical studies on this?

Peter Olson
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    [This article](http://health.howstuffworks.com/human-body/systems/musculoskeletal/question437.htm) mentions a study of 300 people that concluded that it *wasn't*, but I cannot find the actual study. – fredley Mar 25 '11 at 18:10
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    I've been a knuckle-cracker for 28 years, and I'm just fine. And believe me, I'm no genetic superman...unless superman is bald, 5'6", and 20 lbs overweight. – Mr. JavaScript Mar 25 '11 at 20:41
  • This could probably be another skeptics questions, but my Biology teacher at school told us that it's not harmful it's just the sound of dissolved nitrogen escaping from the joint or something along those lines. – Stephen Paulger Mar 25 '11 at 22:21
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    I'm pretty sured that you can be wacked by people around who are annoyed with the sound – Dyppl Mar 26 '11 at 21:16
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    @ajax81 Anecdotal evidence has rather no value. We are all very different. – Jose Luis Oct 21 '11 at 11:12
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    @ajax81: clearly, your knuckle-cracking has caused the balding, medium height, and overweightness. What did you *think* they meant by bad for you? ;) – Domenic Nov 08 '11 at 17:49
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    Does this apply to other joints as well? Cracking my neck gives me a headache... – endolith Jun 04 '12 at 20:33
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    @ajax81 I have an uncle that has been smoking for 40 years, and he's just fine. – Niek Jun 07 '12 at 15:52
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    Just a quick note here: if you feel like you have to crack lots of joints in your body frequently, especially your back / neck, you may have an immuno-arthritic condition called Ankylosing Spondylitis. I suffer from it and, if left untreated, it can leave you in constant pain or in a wheelchair. Go see your doctor! :) – Polynomial Jul 16 '12 at 10:17
  • Great video on BBC: http://www.bbc.com/future/story/20150227-is-it-bad-to-crack-your-knuckles – Brian M. Hunt Mar 01 '15 at 00:26

1 Answers1

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It seems to me like the concern about the negative impact of knuckle cracking brought up in the literature is if it leads to arthritis. Which of course isn't the only harmful thing it could cause.

The Ig Nobel in medicine was in 2009 awarded to Donald L. Unger for research around this very thing. Unger cracked his left hand knuckle systematically for 60 years while leaving his right hand uncracked. Showing that in at least his case it didn't cause any harm. I believe he published his result here.

Beyond that there seem to be two larger studies. The first one published in the British Medical Journal titled Effect of habitual knuckle cracking on hand function shown that there are indeed some problems caused by cracking knuckles:

To investigate the relation of habitual knuckle cracking to hand function 300 consecutive patients aged 45 years or above and without evidence of neuromuscular, inflammatory, or malignant disease were evaluated for the presence of habitual knuckle cracking and hand arthritis/dysfunction. The age and sex distribution of the patients (74 habitual knuckle crackers, 226 non-knuckle crackers) was similar. There was no increased preponderance of arthritis of the hand in either group; however, habitual knuckle crackers were more likely to have hand swelling and lower grip strength. Habitual knuckle cracking was associated with manual labour, biting of the nails, smoking, and drinking alcohol. It is concluded that habitual knuckle cracking results in functional hand impairment.

The second one, published in The Western Journal of Medicine, titled The Consequences of Habitual Knuckle Cracking examined 28 people in a Jewish home for the aged, with an x-ray. It finds no harm:

The data fail to support evidence that knuckle cracking leads to degenerative changes in the metacarpal phalangeal joints in old age. The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer.

So it seems like the the answer is that there's some harm, but it's probably so negligible it's not worth worrying about.

Wai Ha Lee
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Kit Sunde
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    If anything is likely to cause a problem, it's got to be "cracking knuckles with an x-ray". So I guess we can consider the case closed. – Chris Wuestefeld Mar 25 '11 at 19:38
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    HAH. Yes, that would caused some discomfort I'm sure. Fixed. :D – Kit Sunde Mar 25 '11 at 19:46
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    "habitual knuckle crackers were more likely to have hand swelling and lower grip strength" Correlation does not imply causation. Did they check that it's not the other way around? I only have one knuckle that wants to be cracked. – endolith Mar 25 '11 at 21:30
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    "It is concluded that habitual knuckle cracking results in functional hand impairment" "So it seems like the the answer is that there's some harm, but it's probably so negligible it's not worth worrying about" - These seem at odds with each other – Casebash Mar 26 '11 at 00:20
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    "habitual knuckle crackers were more likely to have hand swelling and lower grip strength. Habitual knuckle cracking was associated with manual labour" - and of course, the hand swelling and lower grip strength would never be caused by the manual labour (or the alcohol, for that matter), it must be the knuckle cracking – pdr Mar 26 '11 at 01:36
  • @pdr, you beat me to it. what a junk article to find it's way into the BMJ. No double blind study and no elimination of other artifacts. – iivel Mar 26 '11 at 02:22
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    Have there been any studies on the effects of cracking joints outside of the hands? I habitually crack many joints in my body, including but not limited to: fingers, elbows, shoulders, neck, knees, toes, hips, and lower spine. (For what it's worth, I did lots of manual labor and heavy lifting in summer jobs while in high school, but have a desk job now. I also have a few arthritic conditions but my docs think they are genetic.) – Adam Tuttle Mar 26 '11 at 02:52
  • @Casebash - I don't see why I'd be doing their conclussion a disservice. They said there was some impairment (in one study), that as @pdr points out might be caused by other factors, not that you lost your hand or were unable to use it. – Kit Sunde Mar 26 '11 at 14:34
  • @Kit: But you didn't write down why you favoured the conclusion of the second over the first. You just quoted two sources, then concluded that the second was more reliable without explanation – Casebash Mar 26 '11 at 22:21
  • @Casebash - I didn't write that I favored the second because I didn't. I simply wrote that there didn't seem to be huge problems associated with it (in either study). – Kit Sunde Mar 27 '11 at 01:00
  • @Casebash - After giving this some thought I think what we are really disagreeing on is definition of negligible harm, not the claims to any harm. I wasn't referencing the second study in my conclusion because then I wouldn't have written that there was no harm. Instead I think you are valuing the claimed harm from the first study higher than me (to me it didn't seem like anything to worry about). Perhaps our different views are cultural. – Kit Sunde Mar 27 '11 at 01:43
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    I personally cracked my knuckles habitually (numerous times a day) for several years (6 or 7, I'd guess). It started to hurt me and get on my nerves, since periodically my knuckles would feel like they wanted to be cracked and wouldn't function properly until I cracked them. I decided I didn't like this level of control and apparent damage it was causing me, so I stopped. In a short amount of time I had gone cold-turkey and now haven't cracked them in probably about 8 years. I am of the opinion that it did hurt me, but not irreversibly, and my hands are fine now as far as I can tell. – Ricket Mar 27 '11 at 20:20
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    [Once again](http://skeptics.stackexchange.com/questions/1121/did-a-significant-number-of-sex-workers-experience-abuse-as-a-child/1140#comment-2314), this is correlation, not causation, and thus, **doesn't really tell us anything.** I don't think any of you really *believe* that knuckle cracking causes smoking or alcohol consumption, so I don't see why you'd believe it causes anything else in that list either. – BlueRaja - Danny Pflughoeft Apr 05 '11 at 19:21
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    Great quote, this is just what I though when I read the question: "The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer." Sometimes some people seem to hate knuckle cracking so much they could insult you. :) – Suma Jul 17 '11 at 21:52
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    @BlueRaja: The significant finding here was the lack of a link to arthritis. Correlation tells us little, but a lack of correlation strongly [suggests a lack of causation](http://www.sciencebasedmedicine.org/index.php/evidence-in-medicine-correlation-and-causation/): "In observational studies lack of correlation is easier to interpret than a positive correlation – if there is no correlation between A and B then we can pretty much rule out a causal relationship." – KonradG Sep 16 '11 at 03:38
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    Both of these studies completely miss the possibility that people with knuckle-cracking related ailments consistently died before the age of 45... – Stu Pegg Nov 26 '12 at 16:49