Have you ever wondered what that popping sound is that you hear when you receive a spinal manipulation or adjustment? Patients often refer to it as “cracking” and can find it to be a bit unnerving thinking that they may be having their “back or bones cracked.” Other patients, however, find the sound quite satisfying and feel they only have a beneficial manipulation if they hear that famous “pop”.
The technical term for the sound that you hear is a “Cavitation” which Wikepedia defines as the formation of vapour cavities in a liquid – i.e. small liquid-free zones ("bubbles" or "voids") – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shockwave. So that’s it. When a chiropractor administers a thrust to a joint that is stuck out of alignment there is a release of gas within the synovial fluids within the joint. Once the joint is open then then the synovial fluid lubricates the joint surfaces and normal motion is restored. That is why you feel and move so much better after a chiropractic adjustment.