What Is Knuckle/Joint Cracking?
It would come as a surprise to most people when they discover the reality behind it.
Definition
Our joint are covered by a capsule and
within the space of this capsule is a
special cushion called synovial fluid.(Ref #4)
The "synovial fluid" acts as a lubricant and also contains nutrients for the adjacent bone surfaces.(Ref #1)
The synoval fluid also consist of gases such as:
- Oxygen
- Nitrogen
- carbon dioxide
These gases plus other varieties of gases are continuously dissolved in this fluid.
Therefore when one "cracks" a joint by applying pressure to the joint the stretching of the capsule lowers the pressure inside the joint and creates a vacuum which is filled by the gases.(Ref #1)
This creates a “bubble” which then bursts producing the characteristic “popping” or “cracking” sound.
It takes typicall takes roughly 20 minutes for gases to retunr in the synovial fluid in order to make the cracking sound again.(Ref #1)
This whole process is known as Cavitation. Therefore in truth, when people does this, they're not actually "cracking" any bones as they would think. And that leads to the next question if doing this is dangerous?