New study investigates treatment-associated regrets in prostate cancer. Minimizing successes and magnifying failures? Change your distorted thinking. Cracking your knuckles may aggravate the people around you, but it probably won't raise your risk for arthritis. That's the conclusion of several studies that compared rates of hand arthritis among habitual knuckle-crackers and people who didn't crack their knuckles. The "pop" of a cracked knuckle is caused by bubbles bursting in the synovial fluid — the fluid that helps lubricate joints.
The bubbles pop when you pull the bones apart, either by stretching the fingers or bending them backward, creating negative pressure. One study's authors compared the sudden, vibratory energy produced during knuckle cracking to "the forces responsible for the destruction of hydraulic blades and ship propellers.
Even if knuckle cracking doesn't cause arthritis, there's still good reason to let go of the habit. Chronic knuckle-cracking may lead to reduced grip strength.
And there are at least two published reports of injuries suffered while people were trying to crack their knuckles. As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. It can study very fast processes. The team chose one of its members, Jerome Fryer, to lay on his stomach and put his hand inside the MRI machine. Why Fryer? He has an unusual ability.
As a finger is pulled, tension mounts in the knuckle joint. Fluid rapidly accumulates there. This shows up as a white spot on the MRI picture. Suddenly, a cavity — or bubble — opens. As it does, the knuckle makes a pop. And until it goes away, the knuckle will not be able to crack again. The researchers hope to repeat their study with more volunteers. The theory of bubbles in the joint was first floated in UK researchers JB Roston and R Wheeler Haines hypothesised that cracking the knuckles caused bubbles to form in the synovial fluid; this, they believed, caused the sound.
In , however, another study came along that proposed that it was not the formation, but the collapse of the bubble that produced the audible effect -- in other words, that it was the bursting of the bubble that made a noise.
Other hypothetical sources of the knuckle-cracking noise included stretching ligaments, or the adhesions in the joints snapping -- but the bubble idea has always been the strongest, since X-rays taken directly after cracking a joint show a gas bubble inside that joint.
But whether or not it was the formation or collapse of the bubble had still been something of a mystery. The idea for the study came from Nanaimo chiropractor Jerome Fryer, who approached Professor Kawchuk with a theory. Rather than beat around the bush, they decided to take a direct look using magnetic resonance imaging -- with champion knuckle-cracker Fryer as the guinea pig. Fryer's fingers were inserted, one at a time, into a tube attached to a cable; this tube slowly pulled on each finger until the knuckle cracked.
And, in each instance, it was absolutely the formation of the bubble in the synovial fluid that was associated with the popping sound, occurring within milliseconds. Solving a decades-old mystery was far from the team's only focus, though -- as fun as that was.
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