If you’ve ever laced your fingers together, turned your palms away from you and bent your fingers back, you know how knuckle cracking sounds, but do you know why you crack your knuckles, what causes the sound and whether it’s harmful?

Cracking your knuckles feels good because it stretches the joint and stimulates the nerve endings that are found there.

What causes the popping sound?
A joint is the point where two (or more) bones meet. Ligaments connect the bones to one another and a joint capsule, which secretes a thick, clear liquid called synovial fluid, surrounds the whole area. The synovial fluid lubricates and nourishes the joint while acting as a shock absorber.

When you stretch or bend your finger to pop your knuckle, the joint is pulled apart, expanding the joint capsule. As the pressure of the synovial fluid drops, gases dissolved in the fluid become less soluble, forming bubbles through a process called cavitation. When the joint is stretched far enough, the pressure in the capsule drops so low that these bubbles burst. That rush of gas causes the popping sound that is so satisfying to you and so annoying to everyone else.

To get a second pop, you have to wait 25 to 30 minutes for the carbon dioxide, nitrogen and oxygen to dissolve back into the synovial fluid.

Is knuckle cracking harmful?
While no apparent connection between joint cracking and arthritis has been established, those who habitually crack their knuckles show signs of other types of damage, including soft tissue damage to the joint capsule and a decrease in grip strength. The rapid, repeated stretching of the ligaments surrounding the joint most likely causes this damage. On the positive side, however, there is evidence of increased mobility in the joints right after popping.

 

Sources
http://science.howstuffworks.com
www.huffingtonpost.com