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What Happens when Knuckles Crack?

Adapted from: MDLinx and UC Davis

Recent research at UC Davis Health System looked into two questions about knuckle cracking: What causes the “crack” sound, and does it damage the hand? Ultrasound evaluations showed that the knuckle–cracking sound occurs when gas bubbles form in joints very quickly — faster than the blink of an eye. The study also suggests that the “crack” is caused by bubble forming, rather than bubble bursting.

Examinations by hand specialists found no problems in the joints of knuckle crackers, a finding that contradicts a previous study that suggested that knuckle cracking may cause joint swelling and weaken grip.

Author’s note: I personally used to crack my knuckles. My 8-years-old don does that now. I keep telling him not to do it, but- I guess- I do not have a good reason anymore…

Why Knuckles Crack

Adapted from National Public Radio.

Scientists think they may have solved an old question about the cracking of knuckles: Why does it do that?

The crack apparently comes from a bubble forming in the fluid within the joint when the bones separate. It’s like a tiny air bag inflating. This theory about knuckle-cracking was first proposed in 1947 but challenged in the 1970s.

One guy, who is really good at cracking his knuckles volunteered to put his hand inside a special MRI scanner, and made a movie of the inside of his knuckles as they pulled on the end of each finger to make it crack. What they saw was clear: The cracking sound comes when a bubble forms between the bones of the knuckle joint — not when it collapses.

The discovery challenges the common misconception that knuckle-cracking causes arthritis.

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