One Man Cracked His Knuckles for 60 Years to Disprove a Medical Myth — And He Was Right

If you grew up in an American household, there's a reasonable chance an adult at some point told you to stop cracking your knuckles. Maybe it was a parent, a grandparent, or a teacher. And the warning almost certainly came with a consequence attached: keep doing that and you'll get arthritis.

It's one of those childhood cautions that lodges itself somewhere in the back of your brain and just stays there. Many adults who crack their knuckles still feel a faint twinge of guilt about it, like they're slowly doing something wrong. The thing is, they're not. And a retired California physician named Donald Unger spent roughly six decades making sure someone could actually prove it.

What's Actually Happening When You Crack Your Knuckles

Before getting to the myth, it's worth understanding the mechanics — because the real explanation is more interesting than most people realize.

Your knuckle joints are surrounded by a capsule filled with synovial fluid, which acts as lubrication for the joint. When you pull or bend a finger in a way that stretches that capsule, the pressure inside the joint drops rapidly. That pressure drop causes dissolved gases — primarily carbon dioxide — to come out of solution and form a bubble inside the fluid. The pop you hear is that bubble either forming or collapsing.

For years, scientists debated which of those two events produced the sound. A 2015 study using real-time MRI imaging finally captured the moment clearly: the crack happens when the bubble forms, not when it collapses. After you crack a knuckle, it typically takes somewhere between 15 and 30 minutes for the gases to dissolve back into the fluid — which is why you can't immediately repeat the trick.

That's it. No bones grinding. No cartilage tearing. No structural damage. Just fluid dynamics doing something that happens to sound alarming.

The Man Who Cracked One Hand for Science

Dr. Donald Unger was bothered by the arthritis warning for most of his adult life — bothered enough to do something about it in the most literal way imaginable. For approximately 60 years, Unger cracked the knuckles on his left hand at least twice a day while deliberately leaving his right hand alone. His goal was simple: if the arthritis warning had any truth to it, his left hand should show signs of it and his right hand should not.

After six decades, neither hand had developed arthritis.

Unger published his findings in Arthritis & Rheumatism in 1998, writing with the kind of dry humor that suggests he had been waiting a long time to make this point. He noted that his results, while based on a single subject, offered "evidence that the long-term practice of knuckle cracking does not lead to arthritis of the fingers." He also gently suggested that his mother might want to reconsider her position on the matter.

His work was later recognized with an Ig Nobel Prize — the annual awards given for research that first makes people laugh, then makes them think. It's a fitting honor for a study that was simultaneously absurd in its methodology and completely serious in its conclusion.

What Larger Studies Found

Unger's self-experiment was charming, but the scientific record goes well beyond one man and his hands. A more substantial study published in the same journal examined 300 people over the age of 45, comparing habitual knuckle crackers with non-crackers. The researchers found no increased prevalence of arthritis in the knuckle-cracking group.

There was one finding worth noting: habitual knuckle crackers did show slightly higher rates of hand swelling and marginally reduced grip strength in some studies. The evidence on those points is not entirely consistent across research, but it suggests that if there's any downside to chronic knuckle cracking, it's probably not arthritis — and it's certainly not the dramatic joint destruction the warning implies.

The Arthritis Foundation has explicitly stated that cracking your knuckles does not cause arthritis. The American Academy of Orthopaedic Surgeons has said the same. The myth has been addressed, examined, and dismissed at essentially every level of medical authority. It just hasn't gone away.

How a Harmless Habit Got a Scary Reputation

The origins of the arthritis warning are murky in the way that most folk medical wisdom tends to be — passed down through families and communities rather than sourced from any particular study or physician. The sound itself probably didn't help. A loud pop coming from a joint sounds like something breaking or wearing down, even when it isn't. Human intuition about bodies tends to treat alarming sounds as warning signs, and that instinct isn't unreasonable as a general rule. It just happens to be wrong in this case.

Once the warning became attached to arthritis — a condition most people associate with aging, pain, and joint damage — it gained a seriousness that made it feel medical rather than superstitious. Adults repeated it to children with genuine conviction. Children grew up and repeated it to their own children. The warning acquired authority simply through repetition and longevity, the same way a lot of medical folklore does.

There was no original study. No physician who first observed the connection. Just a plausible-sounding explanation for a weird noise, repeated often enough that it started to feel like fact.

The Takeaway

Crack your knuckles if you want to. You are not damaging your joints, and you will not develop arthritis from the habit. If someone nearby finds the sound annoying, that's a social consideration rather than a medical one — and arguably a more honest reason to stop than the arthritis warning ever was.

The knuckle-cracking myth is a small thing, but it's a useful reminder of how easily a repeated warning can outlive whatever shaky reasoning it was built on. Sometimes the scariest-sounding advice has the least science behind it. And sometimes it takes one stubborn researcher with very patient hands to finally set the record straight.