What really happens when you crack your knuckles


Ever wondered what happens when we crack our knuckles? Well, here’s the answer:

Cracking the knuckles create a gas bubble in the joints which produces that sound. Ultrasound techniques were used to image fingers during a session of knuckle cracking and this finding is been announced in a meeting of the Radiological Society of North America in Chicago.


Some like to crack their knuckles but some totally dislike it. But the good news is that  it does not cause any immediate harm to your hand or body.

Scientists know that the sound isn’t caused by bones or muscles snapping against each other, but it is something to do with the lubricating fluid between many of your joints. This “synovial” fluid stops our bones and cartilage grating too much with each other, and allows us a greater degree of flexibility.

When we stretch our fingers, we release gas into the fluid, which forms small bubbles – this process is known as tribonucleation.

A magnetic resonance imaging (MRI) study was done to look at the formation of these bubbles within the metacarpophalangeal joint (MPJ), the base of the finger, which showed that the noise seemed to come from the initial formation of the bubbles. However, ultrasound imaging can see processes happening within the body up to 100 times faster and detect things up to 10 times smaller than MRI scanners.

A team of scientists, led by radiologist Robert D. Boutin from the University of California, decided to conduct the same study using this technology instead.

Participants were asked to crack each knuckle while being observed through an ultrasound machine. Thirty of the participants were regular knuckle crackers, and 10 were not. After imaging over 400 MPJ cracks, the researchers announced that they saw something far more spectacular than they were expecting.  A bright “explosion” accompanied the bubble formation and collapse.

“What we saw was a bright flash on ultrasound like a firework exploding in the joint,” Boutin said. “It was quite an unexpected finding.”

The flashes in the ultrasound were coupled so consistently with the popping sound that the researchers could predict with 94 percent accuracy which MPJ cracks ‘popped’ just by looking at the images.

The researchers suspect that the cracking and visual flash in the ultrasound images is related to changes in pressure that occur in the synovial fluid, as Boutin explained.

An additional finding of the results is that the joints that are cracked do become significantly more flexible, although only on a temporary basis. Also it has been found that there are no negative health effects associated with habitual cracking while more research needs to be done to confirm that there are no long-term damage. So perhaps it doesn’t hurt to be this sort of crack-addict.

More on this can be read here.