Cracking knuckles: what really happens to your fingers when you pop them (video)

The sound of cracking knuckles is one of the most contentious activities. Some dismiss it, while others firmly believe that such cracking will inevitably lead to arthritis, as reported by IFLScience.

Researchers have long been intrigued by how a small bend of the finger can produce a click loud enough to be heard by everyone in the room. People who crack their knuckles and other joints claim that it helps relieve tension.

In a study of this phenomenon, scientists placed a subject in an MRI machine with sensors on their fingers. This setup allowed them to capture the internal mechanisms of knuckle cracking in real-time. It was long thought that the crack resulted from the collapse of a tiny gas bubble in the synovial fluid surrounding our joints, but this is not the case, according to the MRI study.

In fact, the researchers observed that the cracking process actually created a gas cavity where there had been none before.

This process is called cavitation, which occurs as follows:

The joint surfaces are in their proper positions when a person begins to apply force;

The joint surfaces resist separation;

When a critical force is reached, the joint surfaces separate and create a vacuum-like space that fills with gas. And that’s the loud crack.

The cracking process was also analyzed using ultrasound technology. Ultrasound can visualize processes occurring inside the body 100 times faster and can detect things 10 times smaller than MRI scanners.

"What we saw was a bright flash on the ultrasound, like fireworks in the joint. It was quite unexpected," says Robert D. Butin, a professor of radiology at the University of California, Davis.

The team was confident that the sound of the joint cracking and the bright flash on the ultrasound were related to pressure changes associated with the gas bubble in the joint. While this does not definitively resolve the debate about formation versus destruction, the authors of the study believe that their findings support the bubble formation theory rather than the bursting theory.

Researchers also found that after cracking, the gas cavity remained for some time before disappearing without visible damage to the joint. Knuckle cracking does not seem to have altered the distance between joints in the long term, but it is worth noting that only one participant was involved in the study.

Nonetheless, previous studies have not found "visible immediate adverse" effects from knuckle cracking. Johns Hopkins University also claims there is no evidence linking it to arthritis, which often frightens knuckle-cracking enthusiasts.

However, experts warn that if knuckle cracking is accompanied by pain or other negative symptoms, it is advisable to consult a doctor.

For reference, a Swede made it into the Guinness World Records for his "loud" joints. Olle began cracking his fingers at the age of six, gradually expanding his "sound" range. Before him, the record for the most joint cracks was held by Nepali Kamal Pohrel, who achieved a total of 40.