“What do chiropractors do when they crack your back?”

That "cracking" sound you hear, some describe it as a pop, is actually cavitation of synovial fluid inside the vertebral joints. Synovial fluid is the lubricant that helps keep the lining of the joints, cartilage, from wearing down prematurely. It reduces friction. When a spinal joint has become fixated and out of alignment, what we call a subluxation, the synovial fluid is forced to one side of the joint compartment. When you receive an adjustment the chiropractor is mobilizing the vertebra and realigning it with the ones above and below. When this happens the fluid, within a millisecond, levels out and the sound is caused by cavitation. Two British researchers proved this theory about 15-20 years ago.

One other thing: most chiropractors hate the term "crack your/my back," because it is a spinal adjustment.

Yours in health,

The difference between your back cracking on its own and cracking when the chiropractor works on you is indeed the answer to this question! That being said, let me get to said answer:

When a chiropractor adjusts, you he/she is correcting a misalignment in the spine that is causing dysfunction and damage to the nerve system, which controls the entire body. The doctor will use his or her hands to gently adjust the misaligned bones back into proper alignment, thus taking pressure off of the nerve system, and restoring the body to health, naturally. Don't get me wrong, this may take more than one adjustment to get things perfect, BUT it is well well worth the process.
Good luck and enjoy the chiropractic lifestyle!

Respectfully,

The audible you hear is the cavitation of the vertebrae being placed back into place. The joint being out of alignment is known as a subluxation.

That’s a rather detailed question to answer.
Many things take place. First and foremost to induce motion into a joint that’s not moving properly. Therefore, we have better range of motion, increases immune system, enhances organ function, stimulates brain activity and last but not least inhibits pain by shutting the gate theory of pain. This pain-spasm-pain cycle is stopped or inhibited from the adjustment. Reducing pain and increasing range of motion is a given but when a 3/4 week old baby comes into the office with colic and we adjust that infant using 4oz. of pressure it amazes not only the parents but anyone that witnesses such a miracle from a simple yet complex adjustment. Keep getting adjusted with regularity.

The cracking sound you heard is called an audible release. It is the same thing that happens when one pops his knuckles. Every joint in the body where two bones come together has a joint capsule that surrounds the ends and connects the bones together. That capsule is filled with joint fluid. When the bones are pulled quickly as happens in an adjustment the pressure inside the joint drops. The same drop in pressure happens when one unscrews the lid of a Coke. The release of pressure causes the coke to release gases that are in the fluid. The gases become bubbles and create the cracking or popping sound. The same process occurs in the joints and it creates that sound. It is a good thing and is part of a good adjustment.

We don't crack backs, we adjust the spine. The sound is a release of gases and fluids from between the joints.

They are aligning the joints of your spine. These joints have fluid in them so when they get moved, the change in pressure cavitates and makes the 'pop' sound.