My patients often ask me what makes the “popping” sound during a neck or back adjustment. It is something called cavitation. What is cavitation? Before I get to that, let’s talk a little physics. Everything that is, exists in either one of three forms or states. It is either a solid, a liquid or a gas. The difference between any two of the three is how far apart the molecules are. In a solid, the molecules are very close together. In a liquid, the molecules are a little farther apart. In a gas the molecules are very far apart.

For instance let’s look at H2O or water. It’s three forms are ice, water and steam. The solid form or state is ice, the liquid state is water, and the gas state is steam. By raising the temperature you can melt ice and get water. If you continue to raise the temperature you can boil water and get steam. You can also cool steam into water again and freeze water into ice.

But, did you know you could freeze and boil water at room temperature? Here’s how.

You can do this using pressure. At room temperature H2O is liquid. If you keep the temperature the same or stable and increase the pressure what happens? You will push the molecules closer together and make it a solid or ice. What happens when you decrease the pressure in a liquid? You will pull the molecules apart and form a gas or steam. This is all without changing the temperature. Stay with me… We’re almost there.

Inside nearly all the joints in the body is a fluid called synovial fluid. This fluid lubricates and nourishes the joint. During a chiropractic adjustment the chiropractor/doctor? pulls the joint surfaces apart rapidly. This decreases the pressure inside the joint and pulls the molecules of the synovial fluid apart. When this happens the synovial fluid turns to a gas. This rapid change from a liquid to a gas is what makes the loud pop/popping sound. That is cavitation. If you take an x-ray after an adjustment you can even see a gas bubble in the joint.

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