I get this question at least once a day, especially with new patients. And, I have found that chiropractors are pretty poor at explaining what the “cracking sound” really is. This is one of the reasons why I don’t like to use the word adjustment due to its nebulous definition and most really don’t know what it means. It would be better to use the term mobilization rather than adjustment. It’s more descriptive and people know what mobilizing means. It means to move or to dislodge or to set free.
What is a Cavitation?
The “cracking sound” is actually a physics phenomenon. It is called a cavitation. If you remember back in your high school chemistry class , there was something we learned called a phase change. This is when something changes from solid to liquid or to gas, in this case, it is dissolved gas in a liquid changing back into a gas.
To be clear, some joints in the body contain a liquid called synovial fluid. This liquid is the lubricant for the joint. This lubricant contains some gases that are dissolved within its liquid. The more gas that is dissolved in the liquid the more pressure the joint is experiencing. When chiropractors stretch the joint with a chiropractic mobilization or adjustment usually a high velocity low amplitude thrust, this stretches the joint ligaments just enough to change the atmospheric pressure around the joint which also releases the gas that is dissolved in the fluid into the rest of the joint cavity causing a very quick reverberation off the walls. This is called a cavitation and this is what creates the pop or the cracking sound.
This is the same process that is similar to when you open up a pop can or a champagne bottle and hear the popping sound. This is a release of carbon dioxide gas from a liquid which is bouncing off of the glass and under very high pressure.
Why is This Important?
Because chiropractors are very good at mobilizing joints and stretching the joint to its maximum orthopedic range of motion. This helps to keep a healthy range of motion for all surrounding tissues so that the joint can glide, do its job and not put burden on the surrounding system. Joints that are highly pressurized, restricted and immobile can irritate all tissues including nerve tissue and disrupt normal function of the joint and the neurological system.
So now you know! The popping or cracking sound is really just a physics phenomenon and a depressurization of the joint. It is not bones breaking or grinding or snapping against each other. It is safe and effective. Make sure you are utilizing chiropractic adjustments and mobilizations to promote a well oiled, strong, and optimally functioning mechanical system to dominate your surroundings!