Cracking one's knuckles can mean a lot of things. In older movies, it used to be a sign that a fight was about to break out or that someone was "loosening up" their fingers to get to work, such as sitting down to a typewriter or a piano. In reality, it's probably more often just a nervous tic or a way to relieve stress. And, since what sounds like bone grinding against bone tends to unnerve some folks, knuckle-cracking has also become something people — particularly kids — do just to pester others. That's why, for decades, parents and teachers have passed down to children the same warning their elders impressed upon them: "If you keep cracking your knuckles, you'll end up with arthritis."
The jury is out on whether that age old maxim is an effective deterrent. But regardless of its effectiveness — is it actually, medically true?
"I get asked that fairly frequently," says Charles Cassidy, MD, Orthopedist-in-Chief at Tufts Medical Center. "Usually by mothers who are annoyed and frustrated by their kids doing it."
Dr. Cassidy says that the cracking sound is actually caused by creating negative pressure in the joint fluid between finger bones. This pressure generates air bubbles in the in the joint that burst, producing a "pop." In fact, once the bubble collapses, it sometimes takes up to 20 minutes to form more bubbles, which is why it's difficult to repeatedly crack the same joint in a short span of time.
As for whether the practice is linked with arthritis or any other joint problems later in life, Dr. Cassidy refers to an experiment one California physician performed on himself. He cracked the knuckles on one hand every day for 50 years, while leaving the other hand alone. X-rays of each hand found no difference in terms of arthritis between the two. Subsequent and more scientific and in-depth studies have come to similar conclusions, including a 1990 paper that actually found more inflammation and swelling in subjects who did NOT crack their knuckles.
Instead, Dr. Cassidy says a better indicator of whether or not a young person will one day develop arthritis is genetics. Do their parents or grandparents have arthritis?
"Knuckle-cracking doesn't seem to predispose to arthritis," says Dr. Cassidy. "That's just an old mothers' tale to get kids to stop."
So let the kids crack away. And if the sound becomes intolerable and you don't want to perpetuate the generations-old myth, Dr. Cassidy prescribes asking them to kindly stop, simply ignoring them, or getting a good set of earplugs.