Knuckle-cracking and physics. Or is it chemistry?...

I'm asked this question all the time: "Will cracking my knuckles cause arthritis?"
Well, it depends.
Let's talk about "popping" joints for a minute.

Most of our joints are surrounded by a lubricating substance called Synovial fluid. Within this fluid we have dissolved oxygen, nitrogen and carbon dioxide. The cracking or popping noise that we hear (called a cavitation) is believed to be made by these gases coming out of a liquid solution.
We can hear this noise when the gas makes a transition from liquid to gas form, for example, like water boiling on the stove or the vacuum created by a boat's propeller blades as they pull dissolved oxygen out of the water and leave that trail of bubbles in the wake. In both of these examples, the gases "pop" because either the temperature of the solution has risen (in boiling water) or the pressure on the solution has dropped (vacuum in propeller's wake).

So what is happening in our joints?

Well to use both of the previous examples, if we raised the temperature of a human body to that of boiling water, all the synovial joints would "pop" (not to mention we'd be dead). Or if we were to suddenly decrease the pressure on the fluid in the joint by suddenly stretching open part of the joint's space, it will also cause the gas to pop out of the solution.

The cavitation will only occur when the internal joint space is suddenly decompressed. After a synovial joint "pops" there is a period where it won't pop again. Popping the joint effectively disturbs the gas in the joint and until it settles down again, won't pop again. So for the next 20 minutes or so, these gases will eventually redissolve into the synovial fluid and another decompression will make it pop again.

So back to the knuckle-cracking causing arthritis-

How you crack your knuckles is where the answer lies. Arthritis doesn't come from the popping noise itself, but rather the tendency to grind the joint surfaces together potentially irritating them. So if a person is grinding the surfaces together multiple times a day, day after day, year after year after year...

Grinding the surfaces together is a totally different story than gently tractioning them apart within the normal limits of the ligaments surrounding the joint, which is not damaging in any way.

More to come on this topic in relation to the spine and chiropractic adjustments!