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For other uses, see Knuckle (disambiguation).
The major knuckles of the hand

The knuckles are the joints of the fingers which are brought into prominence when the hand is clenched and a fist is made. The physical mechanism behind the popping or cracking sound heard when cracking joints such as knuckles is still uncertain, although it is widely believed to be caused by synovial fluid filling the vacuum left by the joint's displacement.[1][2]


  1. ^ Johns Hopkins Arthritis Center, Knuckle Cracking and Arthritis
  2. ^ Brodeur R. (1995). "The audible release associated with joint manipulation.". J Manipulative Physiol Ther 18 (3): 155–64. PMID 7790795. 

Public Domain This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.