You’ve probably heard the old wives' tale a thousand times. "Don't crack your knuckles, or you'll get arthritis!" It’s one of those classic parental warnings, right up there with "don't swallow your gum" or "your face will freeze that way." Most of us just rolled our eyes and kept popping our joints. But Donald Unger wasn't most people. He was a man of science, a man of patience, and—perhaps most importantly—a man with a very specific question about his own hands.
The core of the legend centers on one man's sixty-year experiment. But when people dig into the details of this Ig Nobel Prize-winning study, a specific question always bubbles up: Was Dr. Donald Unger right handed or left handed?
Understanding his dominant hand actually matters quite a bit. It wasn't just a quirk; it was the entire control variable for a lifelong medical experiment. Unger decided to use himself as a human guinea pig to see if the arthritis myth held water. To do that, he needed a "control" hand and a "test" hand.
The Sixty-Year Itch (and Pop)
Donald Unger was a physician. He understood the scientific method better than the average person. When his mother, various aunts, and even his mother-in-law told him he was ruining his hands by cracking his knuckles, he didn't just argue. He went to work.
The experiment was brilliantly simple in its design but agonizingly difficult in its execution. For more than sixty years, Unger cracked the knuckles of his left hand at least twice a day. He never cracked the knuckles of his right hand. Think about that for a second. Six decades of conscious restraint. Most of us can't go six days without checking our phones, yet he maintained a strict "no-pop" policy on one side of his body for more than half a century.
So, let's get to the answer. Dr. Donald Unger was right-handed.
This detail is crucial. In most scientific studies involving manual dexterity or physical wear and tear, researchers have to account for "handedness." Why? Because your dominant hand typically does more work. It grips harder, writes more, carries heavier loads, and generally experiences more mechanical stress over a lifetime. By choosing his non-dominant left hand as the "cracking" hand and his dominant right hand as the "control," Unger was actually stacking the deck against his own hypothesis. If cracking caused arthritis, his left hand should have been a mess. If general wear and tear caused arthritis, his right hand should have been the one to suffer.
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The Results that Shocked the (Medical) World
By the time 2009 rolled around, Unger was ready to publish. He looked at his hands. He felt them. He had them X-rayed. He checked for swelling, joint pain, and grip strength.
The result? Nothing. Absolutely nothing.
There was zero difference between the hand he had popped thousands upon thousands of times and the hand he had left alone. Both hands were perfectly healthy. No arthritis. No stiffness. His left hand, despite the decades of clicking and snapping, was identical in function to his right hand.
He famously quipped, "I'm looking at my fingers, and there's not the slightest sign of any arthritis in either hand." Then, with a bit of a wink to his family, he added, "Then I looked up at the heavens and said, 'Mother, you were wrong.'"
Why It Wasn't Just "A Guy Popping His Knuckles"
You might think, "Okay, so one guy didn't get arthritis. So what?"
In the world of medicine, "N=1" studies (studies with only one participant) aren't usually considered definitive. However, Unger’s experiment was so long-term and so consistent that it forced the medical community to take a second look at the mechanics of joint cavitation.
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When you crack your knuckle, you aren't rubbing bones together. You're actually expanding the space between the joint. This reduces the pressure in the synovial fluid (the lubricant in your joints), causing gases like carbon dioxide and nitrogen to form a bubble. When that bubble collapses or the fluid rushes back in, you get that "pop."
Because Unger was right-handed, his right hand was his primary tool for his medical practice and daily life. If the "wear and tear" theory of osteoarthritis were the only factor, his right hand should have shown more age-related degeneration regardless of the cracking. The fact that both hands remained healthy suggests that the human body is remarkably resilient to these types of minor mechanical stresses.
The Ig Nobel Prize and Scientific Legacy
In 2009, Donald Unger was awarded the Ig Nobel Prize in Medicine. If you aren't familiar, the Ig Nobels are a spoof of the actual Nobel Prizes, but they aren't just for jokes. They are awarded for research that "first makes people laugh, and then makes them think."
Unger’s work was the perfect candidate. It sounds ridiculous—a man spending 60 years popping his left knuckles—but it addressed a genuine, widespread medical belief with actual data. His findings aligned with larger-scale studies, like the one conducted in 1990 by researchers at Mount Carmel Mercy Hospital in Detroit. That study looked at 300 people and found no link between knuckle cracking and arthritis, though they did suggest it might lead to some hand swelling or decreased grip strength. Unger, however, didn't even experience those minor side effects.
Honestly, the commitment is the most impressive part. Imagine being 40 years into this. You're at a dinner party. Your right hand feels stiff. You have an overwhelming urge to crack those knuckles. But you don't. You can't. You'd ruin the data. That is a level of discipline that borders on the obsessive, but it’s exactly what gave his "casual" experiment its weight.
Handedness and the Mechanics of the Experiment
Being right-handed meant his right hand was the "perfect" control. In science, you want your control group to be the one that represents the standard or expected condition. For most people, the dominant hand is the one that might naturally develop issues first. By keeping his dominant right hand as the non-cracking hand, Unger ensured that any damage found in his left hand could only be attributed to the cracking, not to over-use.
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Some critics at the time wondered if his left-hand cracking was truly "at least twice a day." He was adamant. It was a ritual. It was part of his identity.
What This Means for You
Does this mean you should go out and pop every joint in your body? Well, not necessarily. While Unger proved that cracking doesn't cause arthritis, it's not entirely consequence-free for everyone.
- Grip Strength: Some studies suggest that habitual, aggressive cracking might lead to a slight loss in grip strength over decades.
- Soft Tissue: There is a tiny risk of injuring the ligaments around the joint if you pull too hard or use a weird angle.
- Social Annoyance: Let's be real—the sound drives some people crazy. Unger’s mother certainly wasn't a fan.
But in terms of the big, scary "Arthritis Boogeyman"? You can breathe easy.
Actionable Takeaways from the Unger Experiment
If you’re a habitual knuckle-cracker or you’re worried about someone who is, here’s the bottom line based on Unger’s sixty-year journey:
- Stop Worrying About Arthritis: The mechanical "pop" of gas bubbles in synovial fluid is not the same as the bone-on-bone friction that causes osteoarthritis. Dr. Unger's experiment, while a single case, reflects the broader medical consensus that cracking is generally harmless to the joints.
- Monitor Your Grip: If you notice your hands feeling weak or swollen, the cracking might be affecting your soft tissue (ligaments and tendons) rather than the bones themselves. Take a break and see if it improves.
- Respect the "Refractory Period": You’ll notice you can't crack the same knuckle twice in a row immediately. It takes about 20 minutes for the gases to re-dissolve into the synovial fluid. Don't force a joint to pop if it isn't ready; that's how you actually hurt yourself.
- Consider the Source: Most medical myths are based on "common sense" that hasn't been tested. Just because something sounds like it should be true (like "popping your joints wears them out") doesn't mean it is.
Donald Unger passed away in 2021, but his legacy lives on in every doctor's office where a patient asks about their knuckles. He proved that curiosity, when paired with extreme patience, can debunk a century of misinformation. Whether you're right-handed or left-handed, his story is a testament to the power of the scientific method—and the satisfaction of finally proving your mother wrong.
To apply this to your own health, start by paying attention to your own "dominant" hand. If you have joint pain, look for the source in your repetitive motions or posture rather than a harmless habit like cracking your knuckles. If the pain persists, consult a physical therapist who can look at your manual mechanics rather than relying on old myths.