cracking your joints is simply the process of moving nitrogen bubbles and cartilage through tight areas.
(i think its nitrogen, been a while since i got told by the Dr what it was...lol)
Cracking the joints doesnt lead to arthritis, it can lead to rheumatism tho.....
arthritis is a blood disease, hence they do blood tests to see if you have it, rheumatism is simply inflamation of the joints, usually due to their being no cartilage left or too much cartilage on one side of a joint. There are other reasons tho so please dont tell me im wrong, i just cant remember what the other reasons are.
The ones i've mentioned are because they are relevant to me. I had Juvenile Chronic Arthritis as a kid, and as a growing adult (28 years old) i have spondlyoarthopathy and onset ankylosing spondylitis. Not much fun, generally painful joints, sometimes very stiff, sometimes too loose. As i get older it gets worse. On average my joints click too much to count. I wake up in the morning, soon as i move my body makes loud deep clunks from various ball and socket style joints (hips, shoulders etc) and once i get up and stretch everything from my neck to my toes cricks out, lower spinal sections make loud clunks too.
By far the oddest one tho, is my collarbone...where it meets at the throat...that clicks...never understood that with it not being a joint, but it does....lol
as for my neck.....you can hear it popping from 10 yards away easily....lol
A Dr once told me, general rule is, if the clicks are loud and happen when you push them to happen without too much pressure, then you should be ok, its just natural to happen. If they happen loudly without you doing anything (ie just moving, say out of bed) then you will likely suffer rheumatism when older. If they happen easily or with force but are more high pitched cricks rather than clunks, then you will probably suffer arthritis when older.