Physicians have argued about the cause of the sound heard when people crack their knuckles for over three hundred years. A new high-tech study of knuckle-cracking has answered at least one of the questions about the source of the noise that comes from cracking one’s knuckles. Dr. Robert D. Boutin, professor of radiology at the University of California at Davis, presented his discovery at the Dec. 1, 2015, session of the annual meeting of the Radiological Society of North America.
Boutin used ultrasound imaging, sonography, and video imaging to capture the exterior and interior activity that occurs when a person cracks their knuckles. The study evaluated 40 men and women. Thirty of the participants were habitual knuckle-crackers and 10 were not.
The ultrasound images revealed a brilliant flash of light that occurred when people cracked their knuckles. This flash of light indicates that a bubble of gas in the joint formed and exploded producing the flash of light and possibly the sound that is heard when a person cracks their knuckles. The study did not determine whether the sound came first or the explosion of the gas bubble came first. The revelation that a gas bubble is formed in the process settles a part of the argument about knuckle-cracking.
The participants were examined for immediate detrimental effects that resulted from knuckle-cracking and none were found. No long-term detrimental effects were found in participants that were habitual knuckle-crackers for as long as 40 years. The researchers reached no conclusion as to any positive of negative effects of knuckle-cracking on joints or other measures of hand strength and dexterity.