Voluntary knuckle cracking is a common habit for between 25-45% of the adult population in the United States. Some people think it’s a harmless occurrence while others say it can cause arthritis in the hands. What does the available research say on the topic?
Before the late 1930s, researchers thought that only unhealthy joints cracked. But a study published in 1938 proved that cracking can also occur in normal joints. In 1947, scientists used radiography (x-rays) to visualize the cracking of the metacarpal phalangeal joint (large knuckle in hand). A slight separation occurred when a distracting force was applied. Once it reached a certain point, a cracking sound was heard when the joint space widened suddenly. This was followed by a twenty-minute period called the “refractory phase,” during which the joint gradually returned to its original resting position. Researchers described a “clear space” on the x-ray that they hypothesized to represent a vapor cavity or “bubble” arising from dissolved gas emitted from the synovial fluid.
However, a study published in 1971 refuted this finding with a conclusion that the formation of the clear space, or bubble, was not the source of joint cracking but rather, the crack was caused by the collapse of the bubble, which they felt could damage the surfaces adjacent to the bubble. Controversy continued over the years with some investigators claiming that joint cracking occurs through ligamentous recoil while others described an additional mechanism known as viscous adhesion, or tribonucleation. This is a process that occurs when two closely opposed surfaces are separated by a thin film of viscous fluid, and when rapidly distracted, viscous adhesion or tension between them releases, causing a negative pressure and creates a vapor cavity within fluid. More recently, a 2015 study using motion MRI found that joint cracking is associated with cavity inception rather than collapse of the bubble.
A 1990 study that included 300 osteoarthritis patients with functional hand impairment found no difference in arthritic symptoms between habitual knuckle crackers and non-knuckle crackers. But, the researchers did observe that the patients in the knuckle cracker group were more prone to hand swelling and weaker grip strength. A pair of 2017 studies found no difference in grip strength between knuckle crackers and non-knuckle crackers in another set of hand osteoarthritis patients, but the patients in the knuckle cracking group did exhibit increased cartilage thickness and a slight increase in range of motion in these knuckle joints. There’s even a study published in 2011 that found habitual knuckle crackers may have a slightly lower risk for osteoarthritis of the hand.
In 1998, Dr. Donald Unger wrote that he spent a half-century cracking the knuckles of his left hand but never his right. After fifty years, he reported no arthritis or other problems in either hand, despite cracking the knuckles in his left hand over 36,500 times. Ultimately, it appears that habitual knuckle cracking is probably safe. That being said, if excessive knuckle cracking stimulates symptoms, then stop and talk to your doctor of chiropractic to see if a more serious condition may be at play or if it may be time to adopt a new habit.