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Doctor Donald Unger cracked the fingers of his left hand for 60 years and never cracked the right to test if the habit causes arthritis, and in the end, there was no difference between the two hands, which earned him the Ig Nobel Prize and debunked one of the most repeated myths about joint health.
There is a myth that almost everyone has heard: cracking your knuckles causes arthritis. But a doctor decided to test this belief in the most radical way possible and dedicated 60 years of his life to an experiment that used his own hands as a laboratory. Dr. Donald Unger cracked the fingers of his left hand daily while keeping his right hand as a control, never cracking it. After six decades of discipline, the result was unequivocal: there was no difference between the two hands, no arthritis, no wear, and no signs of joint damage.
The doctor’s experiment not only debunked a popular belief. It earned Dr. Unger the Ig Nobel Prize in 2009, an award that recognizes research that makes people laugh first and think later. The case became one of the most cited examples of how myths about health can persist for generations without any scientific basis, while a curious enough person, in this case, a doctor with extraordinary patience, can dismantle the belief with a single long-term experiment.
What motivated the doctor to crack his fingers for 60 years
According to a study published in PubMed, the story begins with a scolding from his mother. As a child, the doctor constantly heard that cracking his knuckles would harm his joints and cause arthritis when he got older, a warning that millions of children around the world still hear from their parents and grandparents.
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Instead of simply accepting or ignoring the advice, Unger decided he would prove whether the statement was true or false in the only way a scientist can: by testing.
The doctor established a simple rule that he maintained for six decades: he cracked the fingers of his left hand at least twice a day, every day, and never touched the fingers of his right hand.
The right hand served as the control for the experiment, just as is done in any scientific study where one group receives treatment and another does not. The difference is that the “treatment” lasted 60 years and the laboratory was the researcher’s own hands.
What science says about the sound that comes when someone cracks their knuckles
The crack that is heard when the fingers are pressed is not bone hitting bone, as many people imagine. The doctor and other researchers explain that the sound is produced by the formation and rupture of gas bubbles in the synovial fluid, the substance that lubricates the joints.
When you crack a knuckle, the internal pressure of the joint changes rapidly, causing gases dissolved in the fluid to form bubbles that burst and generate the characteristic sound.
The process does not involve contact between bony surfaces or wear of cartilage, which are the real mechanisms behind arthritis. It’s like opening a bottle of soda: the gas escapes, makes noise, but the bottle is not damaged.
After a few minutes, the gas dissolves back into the synovial fluid and the finger can be cracked again. Dr. Unger understood this mechanics and that’s why he maintained confidence in the experiment over decades.
The result the doctor found after 60 years of experiment
After six decades of cracking only the left hand, the doctor subjected both hands to detailed examinations. There was no difference between the hand that was cracked daily for 60 years and the hand that was never cracked: no arthritis, no inflammation, no signs of differentiated joint wear.
Both hands were in equivalent condition for their age, demonstrating that cracking the knuckles did not produce the damage that popular belief promised.
The doctor’s result is consistent with other research that used imaging tests to compare the joints of people who crack their knuckles with those who do not. No study found evidence that the habit causes arthritis or structural damage to the joints.
Science is clear: cracking your knuckles may annoy those nearby due to the noise, but it does not cause the health problems that generations of parents attributed to the habit.
The Ig Nobel Prize that the doctor received for his six-decade dedication
In 2009, Dr. Donald Unger received the Ig Nobel Prize in Medicine for his 60-year experiment. The Ig Nobel is an award that recognizes unusual scientific research that first makes people laugh and then makes them think, awarded annually at Harvard University.
The award to the doctor recognized both the scientific value of the experiment and the extraordinary discipline of maintaining a research protocol for six decades without interruption.
The doctor’s case has become one of the most cited in scientific dissemination about health myths. It demonstrates that popular beliefs about the human body can survive for centuries without anyone bothering to test them rigorously.
The irony is that it took just one patient researcher to dismantle something that millions of people repeated as absolute truth. The award was not only for proving that cracking your knuckles does not cause arthritis. It was for showing that science requires patience, and sometimes 60 years of patience.
When cracking your knuckles can really be a problem
Although the doctor’s experiment demonstrated that cracking your knuckles moderately does not cause arthritis, there are situations where the habit deserves attention. Forcing the joints before the gas recomposes in the synovial fluid, or applying excessive pressure, can cause discomfort and even momentary injuries.
Prolonged pain or swelling after cracking is not normal and suggests that something different is happening in the joint, warranting a consultation with a professional.
For those who wish to break the habit, the doctor and other specialists recommend identifying what triggers the behavior. Many people crack their knuckles in response to nervousness or anxiety, and replacing the action with alternatives such as stress balls or stretching can be effective.
Cracking your knuckles does no harm as the 60-year experiment proved, but if the habit bothers or causes discomfort, there are ways to modify it without needing 60 years of discipline.
Do you crack your knuckles and have you ever heard someone say that it causes arthritis? What do you think of the 60-year experiment by the doctor who used his own hands to debunk the myth? Share in the comments. Health myths that everyone repeats without questioning deserve this kind of debate, especially when a single patient scientist proves that the belief was wrong.
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