Raymond Brodeur in the Ergonomics Research Laboratory at Michigan State University responds:![Crack Crack](https://cdn-prod.medicalnewstoday.com/content/images/articles/259/259603/person-cracking-their-knuckles.jpg)
- Mar 14, 2019 Cracking your knuckles may sound like it's doing damage to your joints, but the research shows that it doesn't negatively impact the joint or ligaments surrounding it. Here's how you can stop if.
- Apr 16, 2015 Sci-Tech Mystery solved: Why do knuckles crack? For the first time, an MRI video has been taken of cracking knuckles, answering once and for all what makes the audible pop.
To understand what happens when you 'crack' your knuckles, or any other joint, first you need a little background about the nature of the joints of the body. The type of joints that you can most easily 'pop' or 'crack' are the diarthrodial joints. These are your most typical joints. They consist of two bones that contact each other at their cartilage surfaces; the cartilage surfaces are surrounded by a joint capsule. Inside the joint capsule is a lubricant, known as synovial fluid, which also serves as a source of nutrients for the cells that maintain the joint cartilage. In addition, the synovial fluid contains dissolved gases, including oxygen, nitrogen and carbon dioxide.
Nov 08, 2014 While cracking your knuckles might not lead to arthritis, it does appear to have other consequences. In a study of 300 people aged 45 and older, habitual knuckle crackers were again not found to have an increased risk of arthritis in their hands.
The easiest joints to pop are the ones in your fingers (the interphalangeal and the metacarpophalangeal joints). As the joint capsule stretches, its expansion is limited by a number of factors. When small forces are applied to the joint, one factor that limits the motion is the volume of the joint. https://hypeyellow942.weebly.com/blog/netop-vision-hack. That volume is set by the amount of synovial fluid contained in the joint. The synovial fluid cannot expand unless the pressure inside the capsule drops to a point at which the dissolved gases can escape the solution; when the gases come out of solution, they increase the volume and hence the mobility of the joint.
The cracking or popping sound is thought to be caused by the gases rapidly coming out of solution, allowing the capsule to stretch a little further. The stretching of the joint is soon thereafter limited by the length of the capsule. If you take an x-ray of the joint after cracking, you can see a gas bubble inside the joint. This gas increases the joint volume by 15 to 20 percent; it consists mostly (about 80 percent) of carbon dioxide. The joint cannot be cracked again until the gases have dissolved back into the synovial fluid, which explains why you cannot crack the same knuckle repeatedly.
But how can releasing such a small quantity of gas cause so much noise? There is no good answer for this question. Researchers have estimated the energy levels of the sound by using accelerometers to measure the vibrations caused during joint popping. The amounts of energy involved are very small, on the order of 0.1 milli-joule per cubic millimeter. Studies have also shown that there are two sound peaks during knuckle cracking, but the causes of these peaks are unknown. It is likely that the first sound is related to the gas dissolving out of solution, whereas the second sound is caused by the capsule reaching its length limit.
![Crack Crack](https://cdn-prod.medicalnewstoday.com/content/images/articles/259/259603/person-cracking-their-knuckles.jpg)
A common, related question is, Does popping a joint cause any damage? There are actually few scientific data available on this topic. One study found no correlation between knuckle cracking and osteoarthritis in the finger joints. Another study, however, showed that repetitive knuckle cracking may affect the soft tissue surrounding the joint. Also, the habit tends to cause an increase in hand swelling and a decrease in the grip strength of the hand.
Another source of popping and cracking sounds is the tendons and ligaments near the joint. Tendons must cross at least one joint in order to cause motion. But when a joint moves, the tendon's position with respect to the joint is forced to change. It is not uncommon for a tendon to shift to a slightly different position, followed by a sudden snap as the tendon returns to its original location with respect to the joint. These noises are often heard in the knee and ankle joints when standing up from a seated position or when walking up or down the stairs.
What is it that makes that popping sound when you crack your knuckles? If you think it's vacuum cavities forming in the synovial fluid of the joint, give yourself a gold star: a team of researchers led by the University of Alberta Faculty of Rehabilitation Medicine have confirmed that that is precisely what it is.
How? By pulling the fingers of a test subject inside an MRI machine.
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'We call it the 'pull my finger study' -- and actually pulled on someone's finger and filmed what happens in the MRI,' said lead author of the study published in PLOS One, Professor Greg Kawchuk of the Faculty of Rehabilitation Medicine. 'When you do that, you can actually see very clearly what is happening inside the joints.'
The theory of bubbles in the joint was first floated in 1947: UK researchers JB Roston and R Wheeler Haines hypothesised that cracking the knuckles caused bubbles to form in the synovial fluid; this, they believed, caused the sound. In 1971, however, another study came along that proposed that it was not the formation, but the collapse of the bubble that produced the audible effect -- in other words, that it was the bursting of the bubble that made a noise.
Other hypothetical sources of the knuckle-cracking noise included stretching ligaments, or the adhesions in the joints snapping -- but the bubble idea has always been the strongest, since X-rays taken directly after cracking a joint show a gas bubble inside that joint. But whether or not it was the formation or collapse of the bubble had still been something of a mystery.
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The idea for the study came from Nanaimo chiropractor Jerome Fryer, who approached Professor Kawchuk with a theory. Rather than beat around the bush, they decided to take a direct look using magnetic resonance imaging -- with champion knuckle-cracker Fryer as the guinea pig.
Why Do My Knuckles Constantly Crack
'Fryer is so gifted at it, it was like having the Wayne Gretzky of knuckle cracking on our team,' Professor Kawchuk said.
Fryer's fingers were inserted, one at a time, into a tube attached to a cable; this tube slowly pulled on each finger until the knuckle cracked. And, in each instance, it was absolutely the formation of the bubble in the synovial fluid that was associated with the popping sound, occurring within 310 milliseconds.
'It's a little bit like forming a vacuum,' Professor Kawchuk explained. 'As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created and that event is what's associated with the sound.'
Solving a decades-old mystery was far from the team's only focus, though -- as fun as that was. The team believes studying joint cracking could help them better understand joint health -- such as the contradiction between the amount of force required to crack a joint (enough to cause damage to hard surfaces) and the fact that it doesn't appear to do long-term harm.
One thing they found, for instance, was a flash of white in the MRI just before the joint popped -- something no one had ever documented before. Professor Kawchuk believes it was water suddenly being drawn into the joint, and plans to use more advanced MRI to study what happens in the joint just before and after the pop.
Why Do My Knuckles Crack In Winter
Java web browser download. 'It may be that we can use this new discovery to see when joint problems begin long before symptoms start, which would give patients and clinicians the possibility of addressing joint problems before they begin,' he said.
The 1971 team may have missed the mark on the cause of the sound, but they did get at least one thing correct.
What Makes Knuckles Crack
'The data fail to support evidence that knuckle cracking leads to degenerative changes in the metacarpal phalangeal joints in old age,' the study concludes. 'The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer.'