Joint cracking
Cracking joints is the action of moving joints to produce a sharp cracking or popping sound. The most common form of this occurs during deliberate knuckle-cracking. It is possible to crack many other joints, such as those between the back and neck vertebrae, hips, wrists, elbows, shoulders, toes, knees, jaws, and the Achilles tendon area.
Causes
To deliberately produce the clicking sounds, many people bend their fingers into unusual positions. These positions are usually ones that their own muscles are unable to achieve. However, cracking a joint that has been exercised recently is generally recognized to be palliative. For example, bending a finger backwards away from the palm (into extension), pulling them away from the hand (distraction), compressing a finger knuckle toward the palm (into flexion), or twisting a finger about (torsion).
The snapping of tendons or scar tissue over a prominence (as in snapping hip syndrome) can also generate a loud snapping or popping sound.[1]
Source
The physical mechanism is uncertain. Suggested causes include:
- Cavitation within the joint—small cavities of partial vacuum form in the fluid and then rapidly collapse, producing a sharp sound. This explains the popping that can occur in any joint, such as during spinal manipulation. Synovial fluid cavitation is the most likely theory and substantial evidence exists in support of it. Cracking knuckles releases gases from the joints.[2]
- Rapid stretching of ligaments.[1]
- Intra-articular (within-joint) adhesions being broken.[1]
Of these hypotheses, perhaps the most popular is cavitation. When a manipulation is performed, the applied force separates the articular surfaces of a fully encapsulated synovial joint, which in turn creates a reduction in pressure within the joint cavity. In this low-pressure environment, some of the gases that are dissolved in the synovial fluid (which are naturally found in all bodily fluids) leave the solution, making a bubble, or cavity, which rapidly collapses upon itself, resulting in a "clicking" sound. This process is known as cavitation. The contents of the resultant gas bubble are thought to be mainly carbon dioxide.[3] The effects of this process will remain for a period of time known as the "refractory period", which can range from a few seconds to some hours while it is slowly reabsorbed back into the synovial fluid. There is some evidence that ligament laxity may be associated with an increased tendency to cavitate.[4]
Repercussions
The common parental advice "cracking your knuckles gives you arthritis" is not supported by any evidence. A study concluded that 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 in the study participants and their families. It was concluded that habitual knuckle-cracking results in functional hand impairment and therefore should be discouraged.[5]
Medical doctor Donald Unger conducted an experiment in which he regularly cracked the knuckles of his left hand for fifty years while not manipulating those of his right. No arthritis or other ailments formed in either hand, and he was awarded 2009's Ig Nobel Prize in Medicine.[6]
See also
- Crepitus – sounds made by joints
- Joint manipulation
References
- ^ a b c Protopapas M, Cymet T, Protapapas M (1 May 2002). "Joint cracking and popping: understanding noises that accompany articular release". J Am Osteopath Assoc. 102 (5): 283–7. PMID 12033758.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Brodeur R. (1995). "The audible release associated with joint manipulation". J Manipulative Physiol Ther. 18 (3): 155–64. PMID 7790795.
- ^ Unsworth A, Dowson D, Wright V. (1971). "'Cracking joints'. A bioengineering study of cavitation in the metacarpophalangeal joint". Ann Rheum Dis. 30 (4): 348–58. doi:10.1136/ard.30.4.348. PMC 1005793. PMID 5557778.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Fryer, Gary and Jacob, Mudge and McLaughlin, Patrick (2002). "The Effect of Talocrural Joint Manipulation on Range of Motion at the Ankle". Journal of Manipulative and Physiological Therapeutics. 25 (25): 384–390. doi:10.1067/mmt.2002.126129. PMID 12183696.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Castellanos J., Axelrod D. (1990). "Effect of habitual knuckle cracking on hand function" (PDF). Annals of the Rheumatic Diseases. 49: 49(5):308–9. doi:10.1136/ard.49.5.308. PMC 1004074.
- ^ Mirsky, Steve (December 2009). "Crack Research: Good news about knuckle cracking". Scientific American. Retrieved 16 December 2009.