Basically, your thumb is the only part of your body that has saddle joints. the bones in your saddles joint is responsible for moving back and forth, side to side. these joints are free enough to make any motion in your body. They are the only joints that can do 360 degrees and rotate with their own axis. But, because of its free moving, it is prone to any dislocation compared to other movable joints.
your thumb could bend in other ways and could be moved in a 360 degrees if it was a ball and joint, if it was a pivot it could only move in a straight line and not bend like we are used too, the thumbs are opposable so humans can grab things if a different joint is used it can have a harsh affect on the human structure and functions, a major consequence is that if this evolution happened suddenly now out technology could not comprehend with this evolution and we could lose our ability to use now day tools.
(i got this from somebody else but scored 100% so thought I'd share it. creds to that person)
