Debunked Myths

The loud pop of a knuckle crack has been met with parental warnings for generations, accompanied by the grim prognosis of crippled, arthritic hands. The logic seemed unassailable: that grating sound must be the sound of grinding bone or tearing cartilage, a sure path to joint destruction. It’s a warning born from a place of concern and a visceral dislike of the sound itself.

Science, however, delivers a satisfying pop of its own to this myth. The sound comes from a process called cavitation. Synovial fluid, which lubricates our joints, contains dissolved gases. When you stretch the joint, you create a pressure drop that allows these gases to rapidly form bubbles. The pop is the sound of those bubbles collapsing. It’s essentially the same principle as opening a soda bottle. To definitively debunk the myth, Dr. Donald Unger performed a 60-year experiment on himself, cracking the knuckles of his left hand at least twice a day while never cracking his right.

The result? After six decades, he found no difference in arthritis or any other joint problems between his two hands. His dedication earned him an Ig Nobel Prize. Larger studies have confirmed his findings, showing knuckle crackers are no more likely to develop arthritis than anyone else. The myth persists due to a classic logical fallacy: since arthritis is common and knuckle cracking is common, people assume causation when they see both. It’s a powerful lesson in how our instincts about cause and effect can be profoundly misleading.