Dynamic spinal rod and method for dynamic stabilization of the spine
A dynamic spinal rod for connecting levels of a dynamic stabilization system to support the spine while providing for the preservation of spinal motion. Embodiments of the dynamic stabilization system have an anchor system, a deflection system, a vertical rod system and a connection system. The deflection system provides dynamic stabilization and load-sharing. The dynamic spinal rod connects different levels of the construct in a multilevel construct. The dynamic spinal rod cooperates with the deflection system to further reduce stress exerted upon the bone anchors and spinal anatomy.
1. A spinal rod adapted to stabilize the spine, wherein the spinal rod comprises:
an elongated rod having a first end, a second end and a longitudinal rod axis;
a housing at the first end of the of the rod;
a rod bore passing through the housing perpendicular to the rod axis;
a spherical pocket within the bore;
a ball-shaped mount trapped within the spherical pocket;
a ball bore passing through the ball-shaped mount and adapted to receive a post; and
the ball-shaped mount being dimensionally stable such that when the ball-shaped mount is secured to a post, the ball-shaped mount can still pivot and rotate within the spherical pocket of the elongated rod thereby enabling the elongated rod to be secured to the post while allowing the elongated rod to pivot and rotate relative to the post.
2. The spinal rod of claim 1 , wherein the spinal rod comprises a ring-shaped fastener which forms a part of the spherical pocket and secures the ball-shaped mount within the spherical pocket.
3. The spinal rod of claim 2 , wherein the ring-shaped fastener is threaded and is mounted in a threaded region of the rod-bore.
4. The spinal rod of claim 3 , wherein the ball bore is threaded and adapted to secure the ball-shaped mount to a threaded post of a bone anchor.
5. The spinal rod of claim 4 , wherein the ball-shaped mount has a tool engagement feature which is adapted to permit the ball-shaped mount to engage and be turned by a tool to secure the ball bore to a threaded post of a bone anchor.
6. The spinal rod of claim 1 , wherein the ball-shaped mount comprises cobalt chrome.
7. The spinal rod of claim 1 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount; and
the bone screw is configured such that the post may deflect relative to the threaded shaft in response to a load placed on the post by the spinal rod.
8. The spinal rod of claim 1 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount;
the bone screw is configured such that the post changes in angle relative to the threaded shaft in response to a load placed on the post by the spinal rod; and
the spinal rod is configured such that the rod may pivot relative to the post sufficiently to compensate for changes in angle of the post relative to the threaded shaft of the bone screw.
9. The spinal rod of claim 1 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount;
the bone screw is configured such that the post changes in angle relative to the threaded shaft and in response to a load placed on the post by the spinal rod; and
the spinal rod is configured such that the post can pivot relative to the longitudinal rod axis without applying a bending moment to the longitudinal rod.
10. The spinal rod of claim 1 , wherein:
the ball-shaped mount can be compressed to introduce the ball-shaped mount into the spherical pocket of the rod; and
the ball bore is sized so that with a post received in the ball-bore, the ball-shaped mount may not be compressed sufficiently to remove it from the spherical pocket.
11. A spinal rod adapted to span a spinal segment, wherein the spinal rod comprises:
an elongated rod having a first end, a second end and a longitudinal rod axis;
a ball-joint at the first end of the elongated rod, the ball-joint to be secured to elongated rod without locking;
the ball-joint comprising a bore adapted to receive a post of a bone anchor; and
whereby a post of a bone anchor may be secured to the spinal rod at an angle substantially perpendicular to the longitudinal rod axis while allowing the post to change in angle relative to the longitudinal rod axis, after securing the bone anchor to the spinal rod, without applying a bending moment to the elongated rod.
12. The spinal rod of claim 11 , wherein:
the elongated rod comprises, at the first end of the elongated rod, a housing in which the ball-joint is formed;
the housing has a pocket in which is secured a ball-shaped mount in a manner which allows the ball-shaped mount to pivot relative to the housing; and
the ball-shaped mount is adapted to be secured to a post of a bone anchor.
13. The spinal rod of claim 12 , wherein the ball-joint comprises a fastener which secures the ball-shaped mount within the pocket while permitting the ball-shaped mount to pivot relative to the housing.
14. The spinal rod of claim 12 , wherein the ball-shaped mount comprises a threaded bore adapted to secure the ball-shaped mount to a threaded post of a bone anchor.
15. The spinal rod of claim 12 , the ball-shaped mount comprises a tool engagement feature which is adapted to permit the ball-shaped mount to engage and be turned by a tool to secure the ball-shaped mount to a threaded post of a bone anchor.
16. The spinal rod of claim 11 , wherein the ball-shaped mount comprises cobalt chrome.
17. The spinal rod of claim 11 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount; and
the bone screw is configured such that the post may deflect relative to the threaded shaft in response to a load placed on the post by the spinal rod.
18. The spinal rod of claim 11 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount;
the bone screw is configured such that the post changes in angle relative to the threaded shaft in response to a load placed on the post by the spinal rod; and
the spinal rod is configured such that the rod may pivot relative to the post sufficiently to compensate for changes in angle of the post relative to the threaded shaft of the bone screw.
19. The spinal rod of claim 11 , in combination with a bone screw, wherein:
the bone screw comprises a threaded shaft adapted to engage a vertebra and a post that can mount the ball-shaped mount;
the bone screw is configured such that the post changes in angle relative to the threaded shaft and in response to a load placed on the post by the spinal rod; and
the spinal rod is configured such that the post may pivot relative to the longitudinal rod axis without applying a bending moment to the longitudinal rod.
20. A spinal rod comprising:
an elongated rod having a first end, a second end and a longitudinal rod axis;
a mount, the mount including a bore adapted to secure the mount to a post of a bone anchor, the bore having a bore axis, the bore axis forming a angle with the longitudinal rod axis; and
the mount being pivotally connected to the elongated rod by a non-locking joint such that the angle between the bore axis and the longitudinal rod axis may vary, after securing the mount to a post of a bone anchor, between 80 and 110 degrees.