Cracking joints
Encyclopedia
Cracking joints is the action of moving joint
s 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, ankles, knees, jaws, and the Achilles tendon
area.
s 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 recognised to be palliative
. For example, bending a finger backwards away from the palm (into extension
), pulling them away from the hand
(abduction
), 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.
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
. 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.
" is not supported by any evidence. A recent study examined the hand radiographs of 215 people (aged 50 to 89) and compared the joints of those who regularly cracked their knuckles to those who did not. The study concluded that knuckle-cracking did not cause hand osteoarthritis, no matter how many years or how often a person cracked their knuckles. An earlier study also concluded that there was no increased preponderance of arthritis of the hand of chronic knuckle-crackers; 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 and was suggested to result in functional hand impairment. This early study has been criticizied for not taking into consideration the possibility of confounding factors, such as if the ability to crack one's knuckles is associated with impaired hand functioning. As such, it remains unclear if knuckle cracking is in itself associated with any impaired hand function.
Medical doctor Donald Unger regularly cracked the knuckles of his left hand for more than sixty 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.
Joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
s to produce a sharp cracking or popping sound. The most common form of this occurs during deliberate knuckle
Knuckle
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 cognate to similar words in other Germanic languages, such as the Dutch "Knokkel" or German "Knöchel" , i.e., Knöchlein, the diminutive of the German...
-cracking. It is possible to crack many other joints, such as those between the back and neck vertebrae, hips, wrists, elbows, shoulders, toes, ankles, knees, jaws, and the Achilles tendon
Achilles tendon
The Achilles tendon , also known as the calcaneal tendon or the tendo calcaneus, is a tendon of the posterior leg. It serves to attach the plantaris, gastrocnemius and soleus muscles to the calcaneus bone.- Anatomy :The Achilles is the tendonous extension of 3 muscles in the lower leg:...
area.
Causes
To deliberately produce the clicking sounds, many people bend their fingerFinger
A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....
s 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 recognised to be palliative
Palliative care
Palliative care is a specialized area of healthcare that focuses on relieving and preventing the suffering of patients...
. For example, bending a finger backwards away from the palm (into extension
Extension (kinesiology)
In kinesiology, extension is a movement of a joint that results in increased angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed elbow. Straightening of...
), pulling them away from the hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
(abduction
Abduction (kinesiology)
Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
), compressing a finger knuckle
Knuckle
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 cognate to similar words in other Germanic languages, such as the Dutch "Knokkel" or German "Knöchel" , i.e., Knöchlein, the diminutive of the German...
toward the palm (into flexion
Flexion
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal and muscular systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder...
), or twisting a finger about (torsion).
The snapping of tendons or scar tissue over a prominence (as in snapping hip syndrome
Snapping hip syndrome
Snapping hip syndrome is a medical condition characterized by a snapping sensation felt when the hip is flexed and extended. This may be accompanied by an audible snapping or popping noise and pain or discomfort. Pain often decreases with rest and diminished activity...
) can also generate a loud snapping or popping sound.
Source
The physical mechanism is uncertain, and cracking may possibly arise from several different causes. Suggested causes include:- CavitationCavitationCavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
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 manipulationSpinal manipulationSpinal manipulation is a therapeutic intervention performed on spinal articulations which are synovial joints . These articulations in the spine that are amenable to spinal manipulative therapy include the z-joints, the atlanto-occipital, atlanto-axial, lumbosacral, sacroiliac, costotransverse...
. Synovial fluidSynovial fluidSynovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
cavitation is the most likely theory and substantial evidence exists in support of it. Cracking knuckles releases gases from the joints. - Rapid stretching of ligaments.
- Intra-articular (within-joint) adhesionsAdhesion (medicine)Adhesions are fibrous bands that form between tissues and organs, often as a result of injury during surgery. They may be thought of as internal scar tissue that connect tissues not normally connected.-Pathophysiology:...
being broken.
Of these hypotheses, perhaps the most popular is cavitation. When a manipulation is performed, the applied force separates the articular
Articular
The articular bone is part of the lower jaw of most tetrapods, including amphibians, sauropsids and early synapsids. In these animals it is connected to two other lower jaw bones, the suprangular and the angular...
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
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
(which are naturally found in all bodily fluids) leave the solution, making a bubble
Liquid bubble
A bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...
, or cavity
Cavity
A cavity is a hole. It may refer to:*Dental cavity, damage to the structure of teeth*Body cavity, a fluid filled space in many animals where organs typically develop*Cavity wall, a wall consisting of two skins with a cavity....
, which rapidly collapses upon itself, resulting in a "clicking" sound. This process is known as cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
. The contents of the resultant gas bubble are thought to be mainly carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. 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
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
. There is some evidence that ligament laxity
Ligamentous Laxity
Ligamentous laxity is a term given to describe "loose ligaments."In a 'normal' body, ligaments are naturally tight in such a way that the joints are restricted to 'normal' ranges of motion. This creates normal joint stability...
may be associated with an increased tendency to cavitate.
Repercussions
The common advice that "cracking your knuckles gives you arthritisArthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
" is not supported by any evidence. A recent study examined the hand radiographs of 215 people (aged 50 to 89) and compared the joints of those who regularly cracked their knuckles to those who did not. The study concluded that knuckle-cracking did not cause hand osteoarthritis, no matter how many years or how often a person cracked their knuckles. An earlier study also concluded that there was no increased preponderance of arthritis of the hand of chronic knuckle-crackers; 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 and was suggested to result in functional hand impairment. This early study has been criticizied for not taking into consideration the possibility of confounding factors, such as if the ability to crack one's knuckles is associated with impaired hand functioning. As such, it remains unclear if knuckle cracking is in itself associated with any impaired hand function.
Medical doctor Donald Unger regularly cracked the knuckles of his left hand for more than sixty 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
Ig Nobel Prize
The Ig Nobel Prizes are an American parody of the Nobel Prizes and are given each year in early October for ten unusual or trivial achievements in scientific research. The stated aim of the prizes is to "first make people laugh, and then make them think"...
in Medicine.