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Snap, Crackle, Pop!

In my last post I took aim at trying to dispel an old chiropractic myth that bones or joints somehow end up “out” of place and need to be physically realigned via joint manipulation.  We have already established that this is not literally the case – but what about that satisfying (or terrifying for some!) crunch, click, pop, or crack that results from a chiropractic adjustment/manipulation?  Isn’t that the result of a misplaced bone slotting back into its correct location?  Sorry to be the bearer of bad news, folks, but no – it’s just an air bubble.  Let me explain.

Most joints in the human body are considered “synovial” joints because they are encapsulated and lined with a special tissue that creates fluid when moved or distorted. This fluid ends up inside the joint cavity and acts to lubricate and nourish the inside of the joint.  Because there is no direct blood supply to the inner aspect of the joint, synovial fluid also contains gasses and nutrients to keep the joint healthy from the inside.  So, in essence, we’ve got an enclosed capsule filled with a mixture of fluid, gasses and nutrients.  Still with me?  Good.

Okay, now let’s go back to high school science class.  At a certain atmospheric pressures, gasses can exist dissolved in fluid.  However, when that pressure changes (ie. increases during a joint manipulation or adjustment) the substances tend to like to separate into their more pure forms – fluid with fluid, gas with gas.  And, because the entire system is sealed within the joint cavity and there isn’t anywhere for the pressure to escape, increasing pressure to the point of a cavitation (or “pop”) – the formation of an air or gas bubble when it separates from the fluid – is quite simple when applying a specific amount of force from an external source (in this case a chiropractor or physiotherapist).  Recent MRI studies of joints being “cracked” have actually confirmed this phenomenon.

Phew!

So, considering the above information, can excessive knuckle “cracking” give you arthritis?  Likely not.  Creating pressure in your knuckles to the point of cavitation does not cause bones to rub or excessive wear and tear at the joints in question – it just annoys your parents!