“Harmless” is overstating it, however, argue experts who have studied the fine print of the research. Even as there’s no strong link to arthritis — specifically osteoarthritis, the degeneration of the cartilage cushioning the ends of bones — cracking knuckles, they conclude, may still harm your hands.
Seattle neurosurgeon Rod Oskouian is the most recent researcher to jump into this small but lively tributary of mainstream science, as co-author of a 2018 review of knuckle-cracking studies in the journal Clinical Anatomy.
Oskouian and his three colleagues pored over 26 sometimes-contradictory papers regarding the mechanisms and effects of knuckle cracking, beginning with a 1911 German treatise titled “On the Dispute About Joint Pressure.” He did so, he said, after becoming fascinated by the universal inability of his students through the years to explain what makes that cracking noise.
Modern scholars now agree that bones themselves aren’t cracking, but rather that the movement creates a bubble of gas in the synovial fluid lubricating the joints. Researchers still don’t know if it is the bubble’s formation or subsequent pop that makes the noise, but Oskouian said the mechanics are similar to a chiropractor’s “adjustment” of the spine, which also elicits a cracking sound.
Joining with several of their predecessors, Oskouian and his colleagues concluded that researchers have yet to show any reliable association between knuckle cracking and arthritis. A 2017 study of 30 knuckle crackers offered evidence that the habit even increased range of motion.
But that still doesn’t give knuckle-crackers a pass — especially not if they do it a lot and for a long time, or have a preexisting problem.
“Knuckle cracking over the years will cause repetitive trauma to the joints and cartilage,” Oskouian said in a telephone interview.
Studies he cited in his review suggest that long-term knuckle cracking can cause significant damage short of arthritis, stressing and ultimately degenerating cartilage. In 2017, a team of Turkish scientists who examined 35 people who cracked their knuckles more than five times a day found that while it didn’t appear to affect grip strength, it was associated with a thickening of the metacarpal cartilage, a potential early sign of damage that can lead to osteoarthritis.
A more ambitious 1990 study of 300 participants over 45, including 74 habitual knuckle crackers, found that while, again, the crackers had no greater rates of arthritis, they were more likely to have swollen hands and, in this case at least, weaker grips.
“Habitual knuckle cracking results in functional hand impairment,” concluded the two authors, based at the former Mount Carmel Mercy Hospital in Detroit. For good measure, they also noted that habitual knuckle crackers were also more likely to do manual labor, bite their nails, smoke and drink alcohol.
Orthopedists vary in how seriously they regard knuckle cracking as a health threat. Oskouian ventured that the habit is probably harmless for most people, adding that most of his patients seem to abandon the practice after a few years or so.
Yet for perhaps as much