Snap, Crack, Pop: What Joint Sounds Really Mean

It’s harmless to be a crack addict (e.g. cracking your knuckles), the hazards of trusting others to crack you, and what those other sounds your joints make actually mean.

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I cracked my knuckles while at work the other day and a patron looks at me like a mother scolding her toddler and says “You know cracking your knuckles causes arthritis. You wouldn’t want to deal with that down the road now would you?” Being the nice young man that I am, I just smiled and nodded. But I really wanted to explain to her that cracking your own joints is harmless! That’s why I am going to talk about how it’s harmless to be a crack addict (e.g. cracking your knuckles), the hazards of trusting others to crack you, and what those other sounds your joints make actually mean. So prepare yourself for some snappy puns, and let’s get started on this poppin post!
 
Tribonucleation
Tribonucleation is the formation of tiny bubbles between two submerged surfaces when those surfaces are suddenly pulled apart (A.K.A. knuckle cracking). What this means is that during a the cracking process the opposing knuckle joint surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. We know this, due to a very cool study where a person cracked their knuckles during an MRI showing that the cracking is due to cavity inception rather than collapse of a pre-existing bubble (1). In other words, if you want to get your crack on you must generate enough force to overcome tension within the joints (synovial) fluid that keeps the joint tight (not within the soft tissues). This means that you are disrupting the tension forces that keep the joint surfaces together that adds stability to the joint itself (2). This is why you feel nice and loose after a good popping. 
Inline image 1
When it comes to the safety/potential for harm, we know that there is no reason to fret. The old wives’ tale of knuckle cracking causing joint arthritis stems from the thought that the joint collapses during and/or after the force is applied (3). However, we now know for sure that the resting joint orientation is not changed by the cracking event. Furthermore, there is some pretty good research out there showing that cracking your knuckles won’t cause harm (4)… unless it annoys those around you enough for them to cut your fingers off.
Inline image 1
 
What About My Back?!?!
Cracking backs is a practice used by Doctors of Osteopathy, Physical Therapist, and of course Chiropractors. Although the latter of the professions may suggest otherwise, what happens during a back crack is cavitation of a spinal facet joint… same as with the knuckles (5). And what does this “treatment” do? Well it can relieve back pain by taking pressure off sensitive nerves or tissue, increase range of motion, restoring blood flow, reducing muscle tension, and, like more active exercise, promote the release of endorphins within the body to act as natural painkillers. Of course these effects last for about 5 minutes, so a spinal manipulation should be considered one part of a therapy, and not THE therapy (6). Anyone who says otherwise is either lying, or selling you something (The Princess Bride shout out).
 
The Neck
Here’s where things get serious. First of all, we know that cracking the neck is not super beneficial for resolving pain compared to medication (7). Second, we know that neck manipulations come with a rare, but serious, side effects such Cervical Artery Dissection, stroke, and even death (8). I’ll end this brief segment by saying that the risks simply do not justify the reward.
 
Clicking, Crunching, Snapping & The Others
You may notice that not all joints make the same noises. In fact, there are lot’s of sounds that your joints can make, and they can often mean different things. Some common places to experience snapping, clicking, popping, or crunching include the chestshoulderforearmhips, and knees. Of these, the knee is the most common area to experience some form joint sound. Crepitus is the formal term for popping or cracking under the patella (kneecap) and can mean different things depending on where you experience it or feel pain. For instance, a grinding sensation can indicate arthritis, a popping sensation can mean you have loose tissue (plica) getting caught, and a catching feeling could indicate you have a meniscus disorder. Check out this brief video to learn a bit more about what to lookout for if you have questions on how to determine what your knee issue is.
Finally, I would say that the most important factor in deciding what to do about your joint noises is to ask yourself “is this stopping me from doing the things I want to do?” If the answer is NO, then the issue may resolve on its own in time. If the answer is YES, you should seriously consider seeing your Doctor or a Physical Therapist about it.
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References
1. Kawchuk, G. N., Fryer, J., Jaremko, J. L., Zeng, H., Rowe, L., & Thompson, R. (2015). Real-time visualization of joint cavitation: E0119470. PLoS One, 10(4) doi:10.1371/journal.pone.0119470
2. ROSTON, J. B., & HAINES, R. W. (1947). Cracking in the metacarpo-phalangeal joint. Journal of Anatomy, 81(Pt 2), 165.
3. Unsworth, A., Dowson, D., & Wright, V. (1971). ‘cracking joints’. A bioengineering study of cavitation in the metacarpophalangeal joint. Annals of the Rheumatic Diseases, 30(4), 348-358. doi:10.1136/ard.30.4.348
4. Deweber, K., Olszewski, M., & Ortolano, R. (2011). Knuckle cracking and hand osteoarthritis. Journal of the American Board of Family Medicine : JABFM, 24(2), 169.
5. Patient positioning and spinal locking for lumbar spine rotation manipulation. (2001). Journal of Osteopathic Medicine, 4(2), 65-65. doi:10.1016/S1443-8461(01)80005-8
6. Hegedus, E. J., Goode, A., Butler, R. J., & Slaven, E. (2011). The neurophysiological effects of a single session of spinal joint mobilization: Does the effect last? The Journal of Manual & Manipulative Therapy, 19(3), 143-151. doi:10.1179/2042618611Y.0000000003
7. Gross, A., Langevin, P., Burnie, S. J., Bédard-Brochu, M., Empey, B., Dugas, E.. . LeBlanc, F. (2015). Manipulation and mobilisation for neck pain contrasted against an inactive control or another active treatment. The Cochrane Database of Systematic Reviews, (9), CD004249.
8. Thomas, L. C., Rivett, D. A., Attia, J. R., & Levi, C. (2015). Risk factors and clinical presentation of cervical arterial dissection: Preliminary results of a prospective case-control study. The Journal of Orthopaedic and Sports Physical Therapy, 45(7), 503.

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