Trip Answers

Question answered:10/03/06 Warning! this question is over two years old.

Using TRIP and Medline, we were unable to find an authoritative account for this. We located one review, entitled “The audible release associated with joint manipulation” (1), which says:

 

“The audible release is caused by a cavitation process whereby a sudden decrease in intracapsular pressure causes dissolved gasses in the synovial fluid to be released into the joint cavity. Once a joint undergoes cavitation, the force-displacement curve changes and the range of motion of the joint increases. The gasses released from the synovial fluid make up about 15% of the joint volume and consist of approximately 80% carbon dioxide. Habitual joint cracking does not correlate with arthritic changes, but does correlate with loss of grip strength and soft-tissue swelling. During the crack associated with a joint manipulation, there is a sudden joint distraction that occurs in less time than that required to complete the stretch reflexes of periarticular muscles.

 

It is proposed that the cavitation process is generated by an elastic recoil of the synovial capsule as it snaps back from the capsule/synovial fluid interface.
Because the sudden joint distraction during a manipulation occurs in a shorter time period than that required to complete the stretch reflexes of the periarticular muscles, there is likely to be a high impulse acting on the ligaments and muscles associated with the joint.”

 

We found a Library of Congress response to the question  “What causes the noise when you crack a joint?”, the very brief answer to which they give as “Escaping gases, movement and rough surfaces” but the fuller answer may be of interest to read (2). Other than that and a couple of ‘Student BMJ’ responses (3, 4), we found little to offer.

 

There is specific information relating to temporomandibular joint disorder (TMD) and clicking, for example an eMedicine article entitled “Temporomandibular Joint Syndrome” (5) says the following:

 

“Click, pop, and snap: These sounds usually are associated with pain in TMD. The click with pain in anterior disk displacement is due to sudden reduction of the posterior band to normal position. An isolated click is very common in the general population and is not a risk factor for development of TMD.”

 

However, as this specific context isn’t mentioned in the question we have not included further evidence but could do so if this is required.

 

References

1. Brodeur, R. “The audible release associated with joint manipulation.” Journal of manipulative and physiological therapeutics, March - April 95, 18 (3), pgs 155 – 164.
(http://www.hubmed.org/display.cgi?uids=7790795)
2. Library of Congress Science reference Services ‘Everyday Mysteries’. “What causes the noise when you crack a joint?”
(http://www.loc.gov/rr/scitech/mysteries/joint.html#top)
3.  Edwards, J. “You should know, you're a medic: Clicking joints.” Student BMJ, Oct 97.
(http://www.studentbmj.com/back_issues/1097/data/1097ed2.htm)
4.  Wild, E. “You should know, you're a medic: Do people who crack their knuckles get arthritis?” Student BMJ, Jan 03.
(http://www.studentbmj.com/back_issues/1201/life/477.html)
5.  eMedicine. “Temporomandibular Joint Syndrome”, last updated June 04.
(http://www.emedicine.com/neuro/topic366.htm)

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