This is interesting because I've always been told that if I keep continuing to crack my knuckles, I would get arthritis. Considering that your source is from a medicine website, that would seem to be fairly accurate. Although cracking your knuckles doesn't cause arthritis, it does cause osteoarthritis, which is when the cartilage flakes off. So in some sense, there is damage being caused to the knuckles, it just may not be arthritis.