Deflection rod system with a non-linear deflection to load characteristic for a dynamic stabilization and motion preservation spinal implantation system and method

1. An implant adapted to be implanted in the spine of a patient comprising:

a shield surrounding a shield cavity;

a deflection rod having a proximal end and a distal end;

the deflection rod being disposed in the shield cavity such that the proximal end extends out of the shield cavity and the distal end is connected to said shield;

wherein a proximal portion of the deflection rod is spaced from the shield within the shield cavity such that the proximal portion of the deflection rod can deflect within said shield cavity thereby permitting the proximal end of the deflection rod to deflect in response to a load applied to the proximal end of the deflection rod; and

wherein deflection of the proximal end of the deflection rod has a non-linear relationship with the load applied to the proximal end of the deflection rod.

2. The implant of claim 1 wherein contact between the proximal portion of the deflection rod and the shield surrounding the shield cavity as a result of deflection of the deflection rod increases resistance of said proximal portion of the deflection rod to further deflection.

3. The implant of claim 1 wherein said deflection rod increases in effective stiffness with deflection.

4. The implant of claim 1 wherein said non-linear relationship is dependent upon dimensions of said deflection rod and said shield cavity.

5. The implant of claim 1 wherein said deflection rod becomes stiffer as the load applied to the proximal end of said deflection rod increases.

6. The implant of claim 1 wherein said deflection rod includes an inner rod with an outer shell.

7. The implant of claim 1 wherein said deflection rod includes an inner rod comprised of a super elastic material and a cone shaped outer shell.

8. The implant of claim 1 further comprising a threaded bone anchor connected to said shield.

9. The implant of claim 1 , wherein the proximal end of the deflection rod comprises a mount adapted for attachment of a spinal rod.

10. The implant of claim 1 , wherein the proximal portion of the deflection rod is spaced from the shield within the shield cavity by a distance which decreases going towards the distal end of the deflection rod, wherein said shield cavity is cone shaped.

11. An implant adapted to be implanted in a spine of a patient comprising:

a body including a shield with a shield cavity;

a deflection rod that is mounted in said shield cavity such that a proximal end of the deflection rod extends out of the shield cavity and a distal end is connected to said shield;

wherein a proximal portion of the deflection rod is spaced from the shield within the shield cavity such that the proximal portion of the deflection rod can deflect within said shield cavity thereby permitting the proximal end of the deflection rod to deflect in response to a load applied to the proximal end of the deflection rod; and

wherein said deflection rod has a non-linear deflection to load characteristic.

12. The implant of claim 11 , wherein said deflection rod includes an inner rod and an outer sleeve.

13. The implant of claim 11 , wherein said deflection rod includes an inner rod made of a superelastic material and an outer sleeve made of a polymer.

14. The implant of claim 11 , wherein said deflection rod includes an inner rod and a cone shaped outer sleeve that can spread a load placed on said inner rod along said rod.

15. The implant of claim 11 wherein said shield cavity is cone shaped.

16. The implant of claim 11 , wherein:

said deflection rod decreases in diameter going from the distal end of the deflection rod towards the proximal end of the deflection rod; and

said shield cavity increases in diameter going from the distal end of the deflection rod towards the proximal end of the deflection rod increasing in size along said deflection rod in a direction toward said proximal end of said deflection rod.

17. The implant of claim 11 , wherein contact between the proximal portion of the deflection rod and the shield resulting from deflection of the deflection rod increases resistance of said proximal portion of the deflection rod to further deflection.

18. The implant of claim 11 , wherein said deflection rod increases in effective stiffness with deflection.

19. The implant of claim 11 , wherein said body further comprises a threaded bone anchor.

20. An implant adapted to be implanted in a spine of a patient comprising:

a body including a shield with a shield cavity;

a deflection rod that is mounted in said shield cavity;

said deflection rod including an inner rod made of a super elastic material;

said inner rod having a first end and a second end extending from said cavity;

said deflection rod including an outer shell covering said inner rod;

said outer shell comprised of a bio-compatible polymer;

said outer shell is cone shaped and decreases in size in a direction toward said second end of said inner rod

said deflection rod able to be deflected in said shield cavity and the motion of said deflection rod is limited by the shield cavity;

said shield cavity increasing in size in a direction toward said second end of said inner rod; and

said deflection rod that has a non-linear deflection to load characteristic.

21. The implant of claim 20 wherein said deflection rod deflects less as the load placed on the deflection rod system by a spine of a patient increases.

22. The implant of claim 20 wherein said deflection rod load characteristic is linear for an initial loading zone and then is non-linear for another loading zone with higher loads.

23. The implant of claim 20 wherein said non-linear deflection to load characteristic is dependent upon dimensions of said deflection rod system.

24. The implant of claim 20 wherein said deflection rod becomes stiffer as the load placed on the deflection rod system by a spine of a patient increases.

25. The implant of claim 20 , wherein said body further comprises a bone anchor.

26. The implant of claim 20 , wherein said body comprises a bone screw.

27. The implant of claim 20 , wherein said deflection rod increases in effective stiffness with deflection.