FOR SOME PEOPLE, there’s nothing more satisfying than popping a knuckle. And for others, there’s no sound worse.
But what’s going on when your knuckles pop – where does that sound come from?
A new study shows that it’s not what people previously believed – ie, ‘bubble collapse’, the collapse of a bubble in the joint – but instead a gas cavity forming between the knuckle joints.
The full study can be read here. The researchers studied 10 joints before and during popping, taking images via MRI of the whole process at a rate of 3.2 frames per second.
They discovered:
Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble.
These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities.
Basically, the sound is due to the formation of the cavity, not its collapse.
The black cavity can be seen in this photo on the right.
As for whether knuckle cracking causes arthritis?
An author on the paper told the New York Times that that’s not true at all.
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