Low profile spinal prosthesis incorporating a bone anchor having a deflectable post and a compound spinal rod

1. A spinal stabilization device comprising:

a centering rod having a first end, a second end and a flexible section connecting the first end and the second end;

a ball-rod including at least a partial ball-shaped retainer and a rod;

a first bore extending along a longitudinal axis of the ball-rod and opening through the ball-shaped retainer opposite the rod, wherein the first end of the centering rod is received in the first bore;

a housing;

a socket within the housing, wherein the socket partially encloses the ball-shaped retainer to form a ball-joint;

a channel extending from the socket out of the housing, wherein the rod of the ball-rod extends through the channel out of the housing; and

a second bore in the housing extending from the socket opposite the channel, wherein the second end of the centering rod is received in the second bore;

whereby deflection of the ball-rod bends the flexible section of the centering rod and the centering rod exerts a restoring force to center the rod of the ball-rod within the channel.

2. The spine stabilization device of claim 1 , wherein the channel comprises a frusto-conical surface positioned to contact the rod after a predetermined amount of deflection of the rod from center of the channel.

3. The spine stabilization device of claim 1 , wherein said rod and said ball-shaped retainer are made in one piece.

4. The spine stabilization device of claim 1 , wherein said housing further comprises a threaded bone anchor.

5. The spine stabilization device of claim 1 , wherein said housing further comprises a coupling adapted to connect a spinal implant component to the housing.

6. The spine stabilization device of claim 1 , wherein said ball-rod also includes a threaded mount external to the housing adapted to connect a spinal implant to the ball-rod component.

7. The spine stabilization device of claim 1 , wherein said ball-rod is made of cobalt chrome alloy.

8. The spine stabilization device of claim 1 , wherein said centering rod is made of a super-elastic metal.

9. The spine stabilization device of claim 1 , wherein said centering rod is made of nitinol.

10. The spine stabilization device of claim 1 , wherein the first bore further comprises an enlarged portion within the ball-shaped retainer, wherein the flexible section of the centering rod is received in the enlarged portion of the first bore.

11. A spine stabilization device comprising:

a first element;

a second element; and

a self-centering joint connecting the first element and the second element;

wherein said self-centering joint is a self-centering ball-joint and

wherein the self-centering ball-joint comprises:

a housing having a socket;

a ball-rod received in the socket; and

a centering rod received at least partially within the ball-rod and at least partially within the housing;

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 self-centering ball-joint comprises a limit surface positioned to constrain movement of the self-centering ball-joint.

13. The spine stabilization device of claim 11 , wherein the first element is a bone anchor.

14. The spine stabilization device of claim 11 , wherein the second element is a threaded mount adapted to connect to a spinal implant component.

15. A spinal rod comprising;

a rod having a longitudinal axis;

a rod-end comprising an aperture adapted to be secured to a bone anchor;

and a set screw;

wherein the rod-end is connected to the rod by a joint which permits the rod-end to, at least one of, slide along the longitudinal axis of the rod, and rotate around the longitudinal axis of the rod;

and wherein the set screw is configured to apply a force to the rod to lock the rod relative to the rod-end.

16. The spinal rod of claim 15 , further comprising;

a socket in the rod-end;

at least a partial ball positioned within the socket;

wherein the aperture is located through the partial ball such that a bone anchor secured to the partial ball can pivot and rotate relative to the socket.

17. The spinal rod of claim 15 , wherein the rod-end comprises a substantially cylindrical bore in which a first end of the rod is received.

18. The spinal rod of claim 17 , wherein:

the first end of the rod comprises a circumferential groove; and

wherein the rod-end comprises a pin positioned to engage the circumferential groove to prevent removal of the first-end of the rod from the substantially cylindrical bore.