The noise sometimes heard during an adjustment is called a joint cavitation. A joint cavitation is a normally occurring event that can take place during an adjustment.
The mechanism behind a cavitation has a few supporting theories. They all involve a change in pressure and carbon dioxide. The adjustment creates a rapid change of pressure inside the joint capsule. This creates bubbles of carbon dioxide.
The gas bubbles will either collapse on themselves or release out into the synovial fluid. In both cases, the carbon dioxide absorbs back into the joint.
This is where the “popping” sound comes from. If you have ever “popped” your knuckles, the same overarching theory of cavitation occurs. Although "popping" your knuckles and the adjustment make the same sound, they are not the same thing in principle or application.
A cavitation itself is harmless, but the sound can be surprising. And often when we get surprised, that split second of the unknown can elicit different responses. Our brains are hardwired to respond to that uncertainty on an emotional level. An adjustment and associated cavitation can elicit different emotional responses depending on the person.
Also, a cavitation is not always heard with an adjustment. The quality of an adjustment is not predicated on the presence or absence of the cavitation sound. The goal of the adjustment is to reduce Nerve System disruption, not to make "noise."
Jarek Esarco, DC, CACCP is a pediatric, family wellness and upper cervical specific Chiropractor. He is an active member of the International Chiropractic Pediatric Association (ICPA). Dr. Jarek has postgraduate certification in Pediatric Chiropractic through the ICPA. Dr. Jarek also has postgraduate certification in the HIO Specific Brain Stem technique through The TIC Institute. Dr. Jarek is happily married to his wife Regina. They live in Youngstown, Ohio with their daughter Ruby.