"Cracking joints" and "popping knuckles" are an interesting and poorly understood phenomenon. There are many theories as to why joints crack or pop, but the exact cause is simply not known.
Painless cracking of joints is -- as a rule -- not harmful. However, common sense generally would suggest that the intentional and repetitive cracking of one's joints not only is potentially socially bothersome but also could be physically troublesome when it produces pain.
By age 65, more than half of us will have X-ray evidence of osteoarthritis, a disease in which the cartilage that covers the ends of the bones at the joints breaks down and bony overgrowth occurs. For many, the result is stiffness and pain in the joint.
Although osteoarthritis (or OA) is more common as we age, it is not an inevitable part of aging. As researchers work to understand the causes of osteoarthritis, they are able to offer advice to help prevent the disease or its progression and lessen...
Knuckle "cracking" has not been shown to be harmful or beneficial. More specifically, knuckle cracking does not cause arthritis.
Joint "cracking" can result from a negative pressure pulling nitrogen gas temporarily into the joint, such as when knuckles are "cracked." This is not harmful. "Cracking" sounds can also be heard if tendons snap over tissues because of minor adjustments in their gliding paths. This can occur with aging as muscle mass and action change.
If cracking is accompanied by pain, there could be underlying abnormalities of the structures of the joint, such as loose cartilage or injured ligaments. Some patients with arthritis (inflammation of joints, usually painful), bursitis, or tendinitis notice "cracking" sounds due to the snapping of irregular, swollen tissues.