Crack, Pop and Snap : When you crack your knuckles, what causes the crack? For a long time, we were told cracking our joints caused arthritis. So what is the real story here?

The Chemistry and Physics of Cracking knuckles : Inside the joint capsule of your knuckles is a lubricant, known as synovial fluid, which also serves as a source of nutrients for the cells that maintain the joint cartilage. In addition, the synovial fluid contains dissolved gases, including oxygen, nitrogen and carbon dioxide.

If you take an x-ray of the joint after cracking, you can see a gas bubble inside the joint. This gas increases the joint volume by 15 to 20 percent; it consists mostly (about 80 percent) of carbon dioxide. The joint cannot be cracked again until the gases have dissolved back into the synovial fluid, which explains why you cannot crack the same knuckle repeatedly.

What about Arthiritis? : “It is a myth that cracking your knuckles will cause arthritis,” Dr. Greg Tchejeyan, orthopedic surgeon at Los Robles Hospital told Live Science. “Cracking your knuckles will not cause arthritis. What actually happens is that dissolved gases in the joint fluid are rapidly released, causing the cracking sound.”

Sources and References

http://www.scientificamerican.com/article/what-makes-the-sound-when/

Watch video here.

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