Does Knuckle Cracking Cause Arthritis? A Look at the Science
Doctor Donald Unger famously cracked the knuckles of his left hand at least twice daily for 50 years to test family warnings about arthritis. After examining X-rays of both hands at age 72 in 1998, he found no arthritis or differences between them. While studies show 20 to 50 percent of people crack their knuckles, research indicates the habit does not cause joint damage.
Key points
- Donald Unger performed a self-experiment by cracking the knuckles of his left hand at least twice a day for 50 years while leaving his right hand untouched.
- In 1998, at age 72, Unger took X-rays of both hands and concluded there was no arthritis or noticeable difference between the cracked and uncracked hands.
- Broader scientific studies indicate that between 20 and 50 percent of the global population regularly crack their joints.
- The distinctive popping sound is caused by changes in synovial fluid, which lubricates the meeting points between bones when joints are stretched or bent.
The common habit of knuckle cracking has long been the subject of domestic warnings, most notably the belief that the practice leads to arthritis later in life. To test this hypothesis, a physician named Donald Unger undertook a remarkable 50-year personal experiment. He consistently cracked the knuckles of his left hand at least twice a day, accumulating approximately 36,500 cracks, while completely leaving his right hand alone as a control.
In 1998, at the age of 72, Unger evaluated the results by taking X-rays of both hands. His findings revealed no presence of arthritis in either hand and showed no apparent differences between the hand he had continuously cracked and the one he had not. Although his investigation relied on a sample size of just one, broader scientific research indicates that between 20 and 50 percent of people engage in knuckle cracking.
When individuals pull, twist, or bend their fingers to produce a pop, the physical mechanism involves the joint's synovial fluid, an egg white-like substance that acts as a natural lubricant between bones. Despite the widespread popularity of joint-adjustment videos on social media and the satisfying sensation reported by those with the habit, current evidence suggests that the routine sound does not result in lasting physical damage.
Sources
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