Which Bones Shouldn’t You Crack?

A cracker’s guide to all things that go ‘pop.’


Are you a cracker? Do you like to crack? Is cracking your way of releasing tension after a long day of work?

Well, fellow crack enthusiast who’s probably been told that too much cracking can lead to myriad health issues, here’s a quick anatomy lesson on what’s happening when you hear that satisfying, um… *checks thesaurus* …well, crack.

Many of your joints feature small pockets, or gaps, that are filled with synovial fluid. “Like axle grease, this fluid allows the bones in your joints to glide close to one another without grating,” explains Alon Garay, a hand surgeon in San Diego. “When you pull, twist or otherwise ‘crack’ a joint, you’re expanding the volume of space between your bones. That volume expansion creates negative pressure, which sucks the synovial fluid into the newly created space. This sudden inflow of fluid is the popping you feel and hear when you crack a knuckle or a finger or any joint in your body.”

This might be surprising news if you’re one of the many people who believed that the cracking was the sound of air bubbles in your synovial fluid being popped, but a 2015 study published in the journal PLOS ONE proved it to be the case. Researchers conducted an MRI scan of a finger as it cracked in real time and found that it really was the perfectly harmless sound of fluid rushing into the space. “The more you crack your joint, the more you stretch and loosen both its capsule and the surrounding ligaments,” Garay says. “And the looser those components become, the more easily your joint will pop.

Speaking of busted myths, a lot of people also believe that cracking a joint can lead to arthritis, carpal tunnel or other joint issues later in life, but this, too, is an old wives’ tale. A study from 1990 revealed that those who crack their knuckles are generally more likely to do some form of manual labor. Why that correlation exists is unknown, but as explanations for arthritis and joint pain later in life go, daily hard work with your hands makes a lot more sense than knuckle cracking.

Cracking your knuckles, in fact, is almost certainly not going to hurt you. “Multiple studies have looked into the prevalence of ‘crackers’ among large groups of osteoarthritis patients,” says Garay. “They found no evidence that finger pullers and poppers are more likely to suffer from arthritis than those who don’t crack their knuckles.” In fact, a recent study found that people who cracked their knuckles had exactly the same levels of swelling, weakness, ligament looseness and physical function as those who did not.

Your knees, too, are safe: According to Garay, it’s the negative space that’s created in your joints when the synovial fluid is dissolved that explains the cracking sound you sometimes hear when you bend your legs. “Cavitation [as it’s called] results from a change in joint pressure that allows carbon dioxide, which is normally dissolved in your synovial fluid, to come out of the solution and form a cavity between the joint,” explains Garay. “The inception of the cavity that forms is what makes the cracking noise.” All of which is very similar to what’s going on in your fingers.

Cracking your back is pretty much the same thing, too — although Garay warns that self-neck cracking can cause injuries: Not from the cracking itself, but from muscle pulls or even strained tendons and torn ligaments sustained while twisting and straining for a taste of that sweet, sweet crack. “Self-cracking your neck can compromise your blood supply to your head and neck,” says Garay.

By now, you may be wondering, if cracking is basically just a sound (signifying nothing, no less), what’s the point of going to a chiropractor? Do their crack-happy hands really do you any good at all? “It’s an alternative medicine, which means there isn’t much evidence to support its benefits,” says Garay, adding that, if you feel it helps you, “I don’t advise against it.”

So there you have it, my fellow crack addicts: You can crack until your heart’s content and then crack some more, and nothing bad will happen (provided you don’t twist your own head off).