I broke several bones in my thumb when I was in high school. Could this be why I now have arthritis in my thumb joint?

Injury to a joint, such as a bad sprain or fracture, can cause damage to the articular cartilage. An injury to the basal joint of the thumb--even if it does not injure the articular cartilage directly--can alter how the joint works. This is true for a fracture of the thumb metacarpal bone where the bone fragments don't quite "line up" correctly and heal differently from the way they were before the break occurred. This is similar to any mechanical device or machinery. If the mechanism is out of balance, it tends to wear out faster. A bad thumb fracture early in life can help explain why why you now have problems with thumb arthritis.