Cracking your knuckles is generally not harmful and does not cause arthritis, though it may annoy others.
Short answer
No evidence shows that it causes arthritis.
Research
A 1998 study found no link. A doctor (Donald Unger) cracked the knuckles of one hand for over 60 years and found no arthritis, winning an Ig Nobel Prize in 2009.
What the sound is
Gas bubbles (nitrogen) popping in the joint fluid.
Possible downsides
Rarely, swelling or reduced grip strength in heavy crackers.
See a doctor
If cracking comes with pain or swelling.
What the studies measured
The popping sound comes from gas bubbles in the synovial fluid of the joint. A 2015 MRI study led by Greg Kawchuk at the University of Alberta, published in PLOS ONE, observed a cavity forming in the joint fluid at the moment of the crack, which supports the idea that the sound comes from a cavity forming rather than a bubble collapsing. A 2011 study of 215 people in the Journal of the American Board of Family Medicine found no link between habitual knuckle cracking and hand osteoarthritis.
- Donald Unger, a doctor, cracked the knuckles of only his left hand for more than 60 years and found no arthritis in either hand. He received the Ig Nobel Prize in 2009.
- A 1990 study reported that habitual crackers had lower grip strength and more hand swelling, but later research did not confirm a lasting effect.
- Gas can only re-form in the joint after about 20 minutes, which is why you cannot crack the same knuckle again right away.
When cracking is a concern
Cracking joints that hurt, swell or lock may signal injury, ligament problems or arthritis. Painless popping in knees, shoulders and the spine is common and usually harmless. A doctor should check any joint that cracks with pain, redness, or a loss of motion.
What studies measured
A 2011 study by Castellanos and colleagues in the Journal of the American Board of Family Medicine compared hand X-rays and function in people who cracked their knuckles for decades and those who did not and found no increase in osteoarthritis. A famous self experiment by physician Donald Unger, who cracked the knuckles of one hand for over 60 years and not the other, found no difference and earned him the 2009 Ig Nobel Prize. MRI imaging in 2015 showed that the cracking sound is linked to a cavity forming in the joint fluid, and the gas bubble forms rather than collapses.
When to worry
Cracking that is painful, accompanied by swelling, a locked joint or reduced grip strength should be checked. Some studies, including a 1990 report in Annals of the Rheumatic Diseases, linked habitual cracking with hand swelling and weaker grip, though results are not consistent. Sudden pain after cracking may signal a sprain or ligament injury. Persistent joint pain with morning stiffness longer than an hour can suggest inflammatory arthritis, which needs a doctor.
Prevalence and habits
Surveys suggest about 25 to 54 percent of people crack their knuckles. The sound arises when synovial fluid in the joint capsule pulls apart and a gas cavity forms, and real time MRI work by Kawchuk and colleagues in 2018 showed the cavity forms with the crack. After cracking, the joint typically needs about 20 to 30 minutes before it can crack again, a refractory period.
Arthritis and grip evidence
A 2011 study by Castellanos and Axelrod reported no association between habitual knuckle cracking and hand osteoarthritis among 215 people. A 1998 study by Deweber and colleagues reached the same conclusion for 300 older adults. A smaller study from 1990 reported more hand swelling and lower grip strength in habitual crackers, which later work did not confirm. If cracking hurts, treat the pain, not the sound, and see a doctor.
Based on data from the Journal of the American Board of Family Medicine and the Arthritis Foundation
