Cracking joints consist of the action of moving joints to the point of producing popping or cracking sounds. This commonly occurs during deliberate knuckle cracking. This usually happens in the fingers. However, it can also happen in hips, wrists, elbows, ankles, knees and toes, particularly if they are moved into unusual positions. Cracking or popping usually happens due to cavitation within the joints, in particular cavitation related to synovial fluid.