For other uses, see Knuckle (disambiguation).
"Knuckles" redirects here. For the Sonic the Hedgehog character, see Knuckles the Echidna.

The major knuckles of the hand

Anatomical terminology

The knuckles are the joints of the fingers which are brought into prominence when the hand is clenched and a fist is made. The word is cognate to similar words in other Germanic languages, such as the Dutch "Knokkel" (knuckle) or German "Knöchel" (ankle), i.e., Knöchlein, the diminutive of the German word for bone (Knochen). Anatomically, it is said that the knuckles consist of the metacarpophalangeal[1] (MCP) and interphalangeal (IP) joints of the finger. The knuckles at the base of the fingers may be referred to as the 1st[1] or major knuckles while the knuckles at the midfinger are known as the 2nd[2] and 3rd, or minor, knuckles. However, the ordinal terms are used inconsistently, and can be found referring to any of the knuckles.[3][4]

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.[5][6]


  1. 1 2 Utah Mountain Biking; Thumb Sprain; First as metacarpo.
  2. Second knuckle as thumb's interphalangeal, "anchor knuckle" as metacarpophalangeal
  3. First knuckle as thumb's interphalangeal
  4. First knuckle as distal interphalangeal
  5. Johns Hopkins Arthritis Center, Knuckle Cracking and Arthritis
  6. 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 domain: Chisholm, Hugh, ed. (1911). "article name needed". Encyclopædia Britannica (11th ed.). Cambridge University Press. 

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