Q. Why is there a "popping" sound when you crack your knuckles, and is it dangerous to crack them?

Some reasons have been given for the characteristic "popping" sound associated with someone cracking their knuckles. One reason is that when a joint is contracted, small ligaments or muscles can pull tight and snap across bony protuberances of the joint. Another possibility is that when joint is pulled apart, air can pop out from between the bones, creating a vacuum that produces a popping sound. A third reason which is discovered by British scientists in 1971, is that when pressure of synovial fluid is reduced by slow articulation of a joint tiny gas bubbles in fluid may burst, producing popping sound. Research hasn't shown any connection between knuckle cracking and arthritis. One study found that knuckle cracking may be cause of soft tissue damage to joint capsule and a decrease in grip strength. Rapid, repeated stretching of the ligaments surrounding the joint is most likely cause of damage to soft tissue. Some researchers believe that as bones of the hand aren't fully ossified until approximately age 18, teenager and children who crack their knuckles may deform and enlarge knuckle bones. Although most researchers believe knuckle cracking doesn't cause serious joint damage.