Scan cracks old knuckle debate

Arkansas Democrat-Gazette/CELIA STOREY
Knuckles to illustrate a wire filler  in ActiveStyle.
Arkansas Democrat-Gazette/CELIA STOREY Knuckles to illustrate a wire filler in ActiveStyle.

The unmistakable sound of a knuckle cracking is caused by a gas cavity forming between finger joints, according to a new study.

The cavity, or bubble, forms in the synovial fluid, the lubricant between joints. The discovery was reported in the current issue of the journal PLOS One.

One of the paper's authors, Jerome Fryer, a chiropractor in British Columbia, lay inside a cine MRI machine, which stitches together video from a series of rapid scans. Researchers at the University of Alberta cracked each of his knuckles by pulling on a cable attached to his fingers.

"You'll see the black cavity that occurs just as the cracking occurs" on the video, said Dr. Greg Kawchuk, a professor of rehabilitation medicine at the university and the lead author.

In 1947, researchers in England first theorized that the characteristic popping sound occurs when a gas cavity forms. Then, researchers in the 1970s suggested it was the collapse of the cavity, not the formation, that caused the cracking.

Kawchuk added that knuckle cracking did not cause arthritis. "Those are just tales," he said.

On the contrary, he said, understanding exactly why knuckle-cracking doesn't seem to harm the joints could help researchers develop better therapeutic materials for patients with osteoarthritis and other degenerative joint diseases.

ActiveStyle on 04/27/2015

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