What causes the noise when you crack a
joint?
Your joints can make a variety of sounds: popping, cracking,
grinding, and snapping. The joints that "crack" are the knuckles,
knees, ankles, back, and neck. There are different reasons why
these joints "sound off".
* Escaping gases: Scientists explain that synovial
fluid present in your joints acts as a lubricant. The fluid
contains the gases oxygen, nitrogen, and carbon dioxide. When you
pop or crack a joint, you stretch the joint capsule. Gas is rapidly
released, which forms bubbles. In order to crack the same knuckle
again, you have to wait until the gases return to the synovial
fluid.
A Healthy Joint. In a
healthy joint, the bones are encased in smooth cartilage. Together,
they are protected by a joint capsule lined with a synovial
membrane that produces synovial fluid. The capsule and fluid
protect the cartilage, muscles and connective tissues.
* Movement of joints, tendons and ligaments: When
a joint moves, the tendons position changes and moves slightly out
of place. You may hear a snapping sound as the tendon returns to
its original position. In addition, your ligaments may tighten as
you move your joints. This commonly occurs in your knee or ankle,
and can make a cracking sound.
* Rough surfaces: Arthritic joints make sounds
caused by the loss of smooth cartilage and the roughness of the
joint surface.
An Osteoarthritic Joint.
With osteoarthritis, the cartilage becomes worn away. Spurs grow
out from the edge of the bone, and synovial fluid increases.
Altogether, the joint feels stiff and sore.
Is joint cracking harmful? If you are feeling pain when your joints
pop, than you should seek a health care professional. In terms of
knuckle cracking, some studies show that knuckle cracking does not
cause serious harm. Other studies show that repetitive knuckle
cracking can do some damage to the soft tissue of the joint. It may
also lead to a weak grip and a swelling hand.
(source: Library of
Congress)
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given that some of my joints pop and crack involuntarily, i'm
doomed 
