What's that cracking sound?
Chiropractors are famous for cracking backs - but what exactly is the noise and is it safe?
The fancy term for the cracking, crunching and popping is "cavitation". This refers to the fact a cavity is being formed within the synovial fluid between joints; the synovial fluid is there to help reduce friction between joints as well as supply it with nutrients.
For a long time it was thought that the noise came from gases that are dissolved within the fluid (thought to be mostly carbon dioxide) forming bubbles and popping. However more recently it has been thought that the cracking comes from the formation of a vacuum within the fluid as the pressure drops.
The video below shows the cavity being formed during knuckle cracking:
Other causes of cracking:
Tendons slipping over bone (e.g. snapping hip syndrome)
Rough joint surfaces rubbing together (e.g. osteoarthritis) - this is called "crepitus"
Soft tissue injury (e.g. torn meniscus, ligament injury)
Does cracking cause arthritis?
There is no evidence to support the claim that cracking your joints causes arthritis.