11. A spine stabilization device comprising: a first element; a second element; and a self-centering ball-joint connecting the first element and the second element; wherein the self-centering ball-joint includes, a housing having a socket; a ball-rod received in the socket; and a centering rod having an inner core and an outer sheath, the centering rod received partially within the ball-rod and partially within the housing; and whereby deflection of the ball-rod bends the centering rod and the centering rod exerts a restoring force on the ball-rod.
11. A spine stabilization device comprising: a first element; a second element; and a self-centering ball-joint connecting the first element and the second element; wherein the self-centering ball-joint includes, a housing having a socket; a ball-rod received in the socket; and a centering rod having an inner core and an outer sheath, the centering rod received partially within the ball-rod and partially within the housing; and whereby deflection of the ball-rod bends the centering rod and the centering rod exerts a restoring force on the ball-rod. 12. The spine stabilization device of claim 11 , wherein said inner core of said centering rod is made of a super-elastic metal.