Gotta revive an old thread just to add what a physio therapist told me a couple of years ago when I asked why my wrists, shoulders and fingers tended to crack a few months since I'd had to cut out major 'activities'
Essentially she explained it like this.
If you imagine a stone ball, sitting inside a stone cup. The cup fits the ball almost perfectly, with a slight gap all the way around to allow for movement.
Now imagine grabbing that ball and moving it around inside the cup. Not rolling it, but moving it (think pestle and mortar). It's going to create friction, heat up and begin to fall apart in a very short time.
Nature being clever, invented lubricant fluids (hence the slight gap) which sit between the ball and cup, and gave the cup a small amount of soft padding.
The bad news is that fluid gets pushed about, especially the stuff in the padding (as an example think of the disks in your spine, little sachet's of padding).
simulate that padding with a sachet of sauce like you get at most fast food places, the ones in little rectangular packets. Put it between the ball and the cup.
Push the ball down hard - simulating say, a finger against the fretboard pushing back against the knuckle joint - all the sauce moves aside under pressure...
Rotate the ball, and roll it to one end, and all the sauce goes underneath it to the other... Move the ball back quickly and the sauce is trapped, until eventually it builds enough pressure to push under the ball and fill the other side of the sachet again...... "CRACK! POP!"
That feeling of wanting to crack your knuckles is caused then the pressure in the fluid is pretty big - it's all stuck at one side and you need to relieve it and let it settle back into place under the joint. Of course thats a good thing - prevents you wearing out your finger joints!
However, remember that when you deliberately crack your knuckles, wrist, shoulders, neck, spine, feet, erm.... whatever else people like to crack... You're forcing the joint against it's natural position, and stretching soft tissue in directions they're not meant to stretch - so it's good in moderation, but bad if over done.
Of course she was over simplifying, but the principle seemed sound to me. Any physio's here want to add or counter this?
Curt
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