What actually happens when you crack your knuckles

http://goo.gl/8tQa7c

We've all done it. We have all cracked our knuckles before, but have you ever wondered what is really happening when we hear that sound? Now we know the answer. By using MRI to video-record knuckle cracking in action, researchers have discovered that the unsettling "pop" made by cracking one's knuckles results from the rapid creation of a cavity in the fluid inside the joints.  Study researcher Greg Kawchuk, a professor of rehabilitation medicine at the University of Alberta in Canada, says, "It's a little bit like forming a vacuum. As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created, and that event is what's associated with the sound." Using MRI, the researchers recorded what happened inside Fryer's joint in real time as each of his fingers was pulled slowly until the joints cracked. The creation of a cavity in the synovial fluid (the fluid between the joints) made the sound. "The ability to crack your knuckles could be related to joint health," said Kawchuk. "It may be that we can use this new discovery to see when joint problems begin long before symptoms start, which would give patients and clinicians the possibility of addressing joint problems before they begin."