“What is that popping noise when you adjust my back?”

Have you ever heard someone say that they just got their back “popped” or “cracked” by their chiropractor? I get asked all the time what that means. For everyone who already has an idea of what an adjustment looks like, I am simply going to explain the “pop” or “crack.”

First of all, the technical term for the sound is, cavitation. Wikipedia’s definition is: the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Makes perfect sense, right?

OK, here is how I explain it. Joints are where bones meet. Between the bones is a joint capsule. It is a space filled with fluid that allows the joint to easily move without grinding the bones together. When you open up or close a joint quickly it changes the pressure in the capsule. With a sudden change in pressure, gas that is in the liquid escapes causing a popping sound. It’s is just like opening a soda pop bottle or can which is kept under pressure to keep the carbon dioxide dissolved in the liquid.

So, the next time you hear someone pop their knuckles or get an adjustment just remember that the popping sound is just gas expanding because of a change in pressure.


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