According to a number of studies, there's no conclusive evidence that cracking your knuckles damages your joints.

There's still disagreement over whether the cracking sound is caused by the formation of bubbles in the synovial membrane or their collapse.

One scientist was so keen to find out whether knuckle-cracking could lead to arthritis, he cracked the knuckles on one of his hands for 60 years.



Maybe you're the kind of person who cracks your knuckles every now and then (much to the dismay of fellow coworkers, friends and family). Your mother may have warned you at some point that, in doing so, you're damaging your joints — but how much truth is there in that "old wives' tale"?

Well, going off scientific research, none. The only negative effect of cracking our joints, it appears, is that it disgusts and upsets those around us. It seems that the sound, albeit unpleasant, has absolutely no association whatsoever with joint inflammation, with universities such as Harvard and Johns Hopkins joining the list of scientific institutions that, for years, have denied that cracking one's knuckles can cause arthritis.

Previous studies alluded to the possibility that knuckle-cracking could lead to reduced grip strength or weakened joints, but a 2017 study by the University of California found that those who did click their knuckles had the same levels of swelling, ligament weakness and physical function as those who didn't.

Other research has also dismissed the lack of grip and increased thickness of cartilage among finger-cracking lovers as being down to their divisive habit. The real question that science doesn't seem to be able to answer is why this sound is produced.

So, why do our joints crack?

Cracking is not a phenomenon that's exclusive to the knuckles; the neck, back, shoulders, and wrists can also experience this peculiar "crack" when we manipulate them in a given way. But why do they make that sound?

A little background knowledge of anatomy is always useful: a joint is nothing more than the point of contact between two or more bones. Among the components of a joint is a pouch that covers and seals the bone called the synovial membrane. The synovial fluid that helps protect the joint is released into the joint.

The characteristic cracking sound when knuckles crack is due to a change in pressure and volume within the synovial membrane. By executing the movement of our fingers and suddenly changing the position, the blood pressure change that takes place causes the gases present in the synovial fluid to create bubbles, causing the clicking sound.

In this way, to be able to crack your knuckles again, you need to wait about 20 minutes, during which time the pressure and volume are both restored to their normal state.

Is it the sound of air bubbles forming or of bubbles bursting?

Whether the cracking is due to the creation of the bubbles or the bursting of these bubbles is something scientists have been trying to ascertain for years.

One of the first known studies on the subject, dating back to 1947 according to Reuters, suggested the clicking sound was produced by the formation of bubbles in the fluid between the joints. In 1971, a group of researchers at the University of Leeds claimed in their research that it was actually the collapse of that bubble that made the noise, not the formation.

However, by 2015 the debate was back on the table. A new study published in PLOS ONE put forward the original theory again. Researchers carried out an MRI of a finger being cracked, and suggested the popping sound occurred on the fluid entering the cavity.

In another investigation, 40 patients were analysed under an ultrasound machine while cracking their knuckles. A sudden flash was observed in the joint at the time it cracked.

Radiology professor at the University of California and lead author of the study, Robert D. Boutin, proposed that, as the fingers cracked, the bright flash occuring was the formation of a gas bubble.

Researchers at Stanford University and the Ecole Polytechnique de Paris also published research on the topic in Scientific Reports in March this year, explaining that the cracking occured due to the collapse of small air bubbles in the fluid surrounding the joints. The team then developed a mathematical way of predicting what happened in the joint when it cracked.

In addition to discussing the source of the knuckle-cracking sound, this research also suggested that it was perfectly harmless to hear the noise when cracking the knuckles.

The most unusual experiment of all

One of the most fascinating pieces of research into knuckle-cracking was a study by Donald L. Unger of Thousand Oaks, California.

Unger cracked his own knuckles over 60 years on his left hand, leaving the fingers on his right hand "uncracked". After 60 years, he analysed the progression of arthritis in both hands, finding it was the same in both hands.

His peculiar study was published in Wiley Online Library in 2004, and it earned him the Ig Nobel Prize for Medicine, an award that parodies the real Nobel Prize.

On receiving the award, he said: "Mother, I know you can hear me. Mother, you were wrong! And now that I have your attention, can I stop eating my broccoli, please?"