What happens when you crack your knuckles?

kerry8888

The sound of your knuckles cracking has nothing to do with bones rubbing together or calcium buildup. It's the sudden expulsion of air from the small gaps in the joints. May 06 03, 2:25 PM

sequoianoir

kerry is right. When you crack your knuckles, you are actually pushing the joint either into or out of its normal position. In either case, when you do this, gas, mostly nitrogen, is displaced and escapes from the joint space. This displacement of gas causes the 'popping' and 'cracking' sound of knuckles, and a few other joints. Not all joint 'popping' sounds are caused by escaping gases. In some joints, most notably the hip, the sound is made by ligaments moving over the bone. http://www.coolnurse.com/health_faqs2.htm May 06 03, 9:27 PM