Should you stop cracking your knuckles?

Like a firework exploding in the joint – here's everything you need to know about cracking your knuckles.

Growing up, Donald Unger was warned – by his mother, several aunts, and later his mother-in-law – that constant knuckle cracking would cause arthritis. Determined to prove them wrong, he cracked his left knuckles at least twice a day for 50 years – around 36,500 cracks in total – while leaving his right untouched. 

In 1998, aged 72, he took X-rays of both hands to find out the result of his lifelong endeavour. "There was no arthritis in either hand, and no apparent differences in the two hands," he concluded.

This of course, was a sample size of just one. Studies indicate that somewhere between 20 and 50% of people crack their knuckles. So, is this something that we should be worried about – could every pop, click, and crack be causing lasting damage?

For some a knuckle crack is just a mindless habit. Others like the way cracking their joints feels. But judging by the flurry of chiropractic adjustment videos trending on social media, there's a good number who get a kick out of hearing that snap.

What happens when we crack our joints is actually relatively simple. A joint is where two bones meet, and the ones found in our knuckles, neck, and back are surrounded by synovial fluid – an egg white-like substance that acts as a lubricant. When you twist, pull, and bend your joints to crack them, the space within the joint temporarily expands. This causes the pressure of the synovial fluid to fall, and as a result, gases that were once dissolved in the fluid begin to emerge as bubbles.

The sound of a joint cracking – which is actually the sound of the bubbles that have formed collapsing – can be surprisingly loud, up to 83 decibels. That's roughly the volume of a diesel truck rumbling past at 40 miles an hour (64km per hour). When scientists at the University of California, Davis, viewed a joint that was being cracked using ultrasound, they described the moment of the "crack" as appearing like a firework exploding on the screen.

A mostly harmless habit

It may be noisy, but the sound of your joints popping is "just a normal physiological process", says Kimme Hyrich, a rheumatologist at the University of Manchester in the UK.

But is normal necessarily harmless?

"Obviously there are some red flags like pain or swelling in the joints," says Jay Jagannathan, a neurosurgeon with his own practice in Michigan, in the US, who has seen patients with strains and other issues after cracking their necks too forcefully – something which is not recommended (more on this later).

However, generally speaking, when you feel the urge to crack your joints, it's considered pretty harmless, says Jagannathan.

Some people still worry that vigorous knuckle cracking might result in finger dislocations or tendon injuries, especially when you apply too much........

© BBC