What causes the noise when you crack a joint? Is joint cracking harmful?
The exact mechanism is unclear. Here are some possible causes:
- rapid collapsing of cavities inside the joint ;
- rapid ligament stretching ;
- breaking of intra-articular adhesions ;
- escaping gases from synovial fluid ;
- movements of joints, tendons and ligaments ;
- mechanic interaction between rough surfaces , mostly in pathological situations like arthritis (and it is called crepitus ).
There are no known bad effects of joint cracking [1, 4].
There are no long term sequelae of these noises, and they do not lead to future problems. There is no basis for the admonition to not crack your knuckles because it can lead to arthritis. There are no supplements or exercises to prevent these noises .
And no good effects either:
Knuckle "cracking" has not been shown to be harmful or beneficial. More specifically, knuckle cracking does not cause arthritis .
- Wikipedia contributors, "Cracking joints," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Cracking_joints&oldid=617403659 (accessed July 22, 2014).
- The Library of Congress. Everyday Mysteries. What causes the noise when you crack a joint? Available from http://www.loc.gov/rr/scitech/mysteries/joint.html (accessed 22.07.2014)
- Wikipedia contributors, "Crepitus," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Crepitus&oldid=615557134 (accessed July 22, 2014).
- Johns Hopkins Sports Medicine Patient Guide to Joint Cracking & Popping. Available from http://www.hopkinsortho.org/joint_cracking.html (accessed 22.07.2014)
- WebMD, LLC. Will Joint Cracking Cause Osteoarthritis? Available from http://www.webmd.com/osteoarthritis/guide/joint-cracking-osteoarthritis (accessed 22.07.2014)
Is joint-cracking harmful? No. Donald Unger was told by his mother that he'd get arthritis if he cracked his knuckles so he cracked his left knuckles every day for 60 years but never his right knuckles. He had no arthritis or any other problems in either hand and got a publication (D. L. Unger, "Does knuckle cracking lead to arthritis of the fingers?", Arthritis and Rheumatism 41(5):949–950, 1998 – online version for those with appropriate access) and an Ig Nobel Prize (2009) for his troubles.
OK, so one guy's knuckles prove nothing but who can resist the opportunity to cite an Ig Nobel winner?
A paper was just published that explains this phenomenon in PLOS One, found here. It looks like the sound is caused by the formation of a gas cavity in synovial fluid of the joints. They do mention that contrary to what is stated in the most upvoted answer here, the sound does not come from the collapse of the bubble, but rather its formation.
And in response to the comments, as mentioned in the paper, this does not seem to cause any harm to the meniscus or surrounding tissue.