You should periodically go back to your doctor and get x-rayed. When you damage your vertebrae, the pressure on your discs is insane. That pressure may not do much damage immediately, but sometimes when the bones heal, they heal in a way that keeps pressure on your discs. You may have slipped a couple over the years, and not have noticed it, because its gradual. I cracked 3 vert. in my lower back when I was 14, and when I was 18 the doctors found that 2 discs were shifting. Luckily they caught it early, but my Dad didn't catch his, and had to have a couple surgeries 3 years ago to fix the damage. I've also heard of instances where there are small particles of bone that chip off and cause binding in the spinal column, when they get lodged in tight areas, but that doesn't always show up on x-rays, if I remember what was told to me by my doctor correctly.
[This message has been edited by tex (edited 08-24-2001).]