The knuckles are the
joint
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
s of the
finger
A finger is a prominent digit (anatomy), digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (dactyly, pentadact ...
s. 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
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...
[Utah Mountain Biking]
Thumb Sprain
First as metacarpo. (MCP) and
interphalangeal (IP) joints of the finger. The knuckles at the base of the fingers may be referred to as the 1st
or major knuckles while the knuckles at the midfinger are known as the 2nd and 3rd, or minor, knuckles. However, the
ordinal terms are used inconsistently and may refer to any of the knuckles.
Cracking
The physical mechanism behind the popping or cracking sound heard when
cracking joints such as knuckles was elucidated in 2015 by cine
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...
to be caused by
tribonucleation as a gas bubble forms in the
synovial fluid
Synovial fluid, also called synovia, elp 1/sup> is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articul ...
that bathes the joint. Despite this evidence, many still believe it to be caused by synovial fluid filling the vacuum left by the joint's displacement. In 2009, Donald L Unger was awarded the
Ig Nobel for Medicine for his informal experiment with knuckle cracking. For 50 years, he cracked the knuckles of one hand while not cracking the knuckles of the other during that time. He self-reported no issues with arthritis on either hand.
Does knuckle cracking lead to arthritis of the fingers?
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Gallery
MotorcycleRacingGlove.jpg, Motorcycle racing gloves with titanium knuckle protectors
See also
* Metatarsophalangeal joints
The metatarsophalangeal joints (MTP joints) are the joints between the metatarsal bones of the foot and the proximal bones (proximal phalanges) of the toes. They are analogous to the knuckles of the hand, and are consequently known as toe knuck ...
, also informally known as toe knuckles, the equivalent joints in the toes.
* Metacarpophalangeal joint
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...
References
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Fingers