[[File:|thumb|right|The major knuckles of the hand]] The knuckles are the joints of the fingers and toes, which are brought into prominence when the hand is clenched and a fist is made. The word is derived from Knöchlein, the diminutive of the German word for bone (Knochen). Anatomically, it is said that the knuckles consist of the metacarpophalangeal^[1] and interphalangeal 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]

References

 This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (Eleventh ed.). Cambridge University Press. 

Knuckles is also the name of a Sonic the Hedgehog-related video game character.

A knuckle, in anatomy, is where two bones join in the hands or feet. When talking about humans, knuckles most often refer to the joints in the fingers.

Animal knuckles, such as pig knuckles are sometimes sold as food.