Cracking Your Knuckles: Here’s What Really Happens

People have been trying to figure out what really happens when you crack your knuckles and why it makes that sound. Some theorized that the joints collide with each other, which is why there’s a sound that comes after.

But ask any chiropractor in Salt Lake City or any other place in the country, and they would say that that would be extremely painful. Besides, all joints have cartilage between them, so there’s no way that one bone could hit another bone.

Others theorized that bubbles appear whenever you crack your knuckles and the sound comes from those bubbles popping. But finally, a team of scientists used an MRI to see what really happens when you crack your knuckles.

“Pull my finger”

A group of scientists from the University of Alberta led the experiment and one of their members volunteered to be examined while he cracked his knuckles. What they did was the subject inserted his fingers one by one into a tube, which pulled his finger until it resulted in a cracking noise.

While the tubes were pulling the subject’s fingers, the other scientists used an MRI to see what was happening inside his hand. What they discovered was that when the knuckles cracked, a cavity formed instantaneously and it is this that cavity that creates the sound.

Another team of scientists conducted the same experiment but used a different device to examine what happens to a joint when a person cracks his knuckles. A radiologist from the University of California, Davis led the study and he used an ultrasound to see what happens inside the joints.

Robert D. Boutin said that an ultrasound is much more effective than an MRI in recording any kind of activity inside a human body. Ultrasound machines are also 100 times faster than MRIs. He added that they can also record events that are 10 times smaller than what MRIs are capable of recording. So according to him, the ultrasound is definitely the better equipment for this kind of study.

When they started their study, Boutin and his team saw in their ultrasound results a large flash when the person cracked his knuckles. The flash of light was so intense that it looked like an explosion occurred in his joints.

Boutin said that due to their results, they think that the sound produced from knuckle-cracking is caused by the sudden change in pressure in the joint. He added that their findings may have put to rest the theory that the sound comes from the bubble popping inside the joint.

Boutin said that the sound they heard came before the bubble appeared in their ultrasound, which was the bright light. So it may be that the bubble popping theory may be inaccurate and that the sound comes from the sudden change of pressure in the joint.

Health concerns

Scientists are still looking into the dangers of knuckle-cracking but so far, no evidence has shown that it can lead to arthritis or any kind of joint pain. One doctor even went so far as to see if the hand he cracked knuckles with would develop pain.

A doctor from California cracked his knuckles on one hand, but he kept his other hand free from this activity as the control tool. After 60 years of knuckle-cracking, Donald Unger said that his hand didn’t develop any pain.

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