Deflection rod system dimensioned for deflection to a load characteristic for dynamic stabilization and motion preservation spinal implantation system and method

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

a body including a shield with a shield cavity, the shield cavity having a first end and a second end;

a deflection rod having a fixed end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the fixed end is secured in the first end of the shield cavity and the free end extends out of the second end of the shield cavity;

said deflection rod being spaced from said shield along a first portion of said deflection rod extending from the free end and into the shield cavity such that said first portion of said deflection rod is configured for deflection perpendicular to the longitudinal axis in response to a load applied to the free end of the deflection rod, said deflection of said first portion of said deflection rod being limited by the shield; and

wherein said defection rod comprises a superelastic material.

2. The implant of claim 1 , wherein said deflection rod is spaced from said shield along said first portion of said deflection rod such that after about 0.06 inches of deflection of the free end, the deflection rod has an increased resistance to greater deflection.

3. The implant of claim 1 , wherein deflection of the free end of the deflection rod requires approximately 300 lbs force per inch over a first 0.06 inches of travel and approximately 1000 lbs per inch over a further 0.04 inches of travel.

4. The implant of claim 1 , wherein said deflection of said first portion of said deflection rod is limited by the shield such that deflection of the free end of the deflection rod is limited to about 0.1 inches.

5. The implant of claim 1 including:

said deflection rod includes an inner rod and an outer sleeve; and

said inner rod is made of said super elastic material and

wherein said outer sleeve is made of a bio-compatible polymer and

wherein said inner rod has a diameter of at about 0.08 inches and said outer sleeve has a maximum diameter of about 0.16 inches in a region adjacent the fixed end and tapers at about 2.5 degrees per side going towards the free end.

6. The implant of claim 1 including:

said deflection rod includes an inner rod and an outer sleeve; and

said inner rod is made of Nitinol;

wherein said outer sleeve is made of PEEK; and

wherein said inner rod has a diameter of at about 0.08 inches and said outer sleeve has a maximum diameter of about 0.16 inches in a region adjacent the fixed end and tapers at about 2.5 degrees per side going towards the free end.

7. The implant of claim 6 wherein said outer sleeve has a working length along which the outer sleeve can deflect of about 0.75 inches.

8. The implant of claim 5 wherein said shield has a length of about less than 0.95inches.

9. The implant of claim 6 wherein said shield has a length of about less than 0.95inches.

10. The implant of claim 6 wherein said body has a diameter of about 0.26 inches.

11. The implant of claim 1 wherein said deflection rod that has a non-linear deflection to load characteristic.

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

a body including a shield with a shield cavity, the shield cavity having a first end and a second end;

a deflection rod having a fixed end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the fixed end is secured in the first end of the shield cavity and the free end extends out of the second end of the shield cavity;

said deflection rod being spaced from said shield along a first portion of said deflection rod extending from the free end and into the shield cavity such that said first portion of said deflection rod is configured for deflection perpendicular to the longitudinal axis in response to a load applied to the free end of the deflection rod, said deflection of said first portion of said deflection rod being limited by the shield; and

said deflection rod including an inner rod made of a superelastic material wherein said inner rod is about 0.08 inches in diameter with a working length along which said inner rod can deflect of about 0.84 inches;

said deflection rod including a conical polymer outer shell covering said inner rod;

wherein the outer shell decreases in external diameter going from the fixed end of the deflection rod towards the free end of the deflection rod; and

wherein said shield cavity increases in internal diameter going from the fixed end of the deflection rod towards the free end of the deflection rod.

13. The implant of claim 12 wherein said deflection rod increases in effective stiffness after a predetermined amount of deflection.

14. The implant of claim 12 , wherein said deflection rod has a first resistance to deflection over a first zone of deflection and a second resistance to deflection over a second zone of further deflection and wherein the second resistance is more than double the first resistance.

15. The implant of claim 12 , wherein said deflection rod has a first resistance to deflection over a first 0.06 inches of deflection and a second resistance to deflection over a further 0.04 inches of deflection and wherein the second resistance is more than double the first resistance.

16. The implant claim 12 , wherein said deflection rod has a first resistance to deflection of about 300 lbs per inch over a first 0.06 inches of deflection and a second resistance to deflection of about 1000 lbs per inch over a further 0.04 inches of deflection.

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

a body including a shield with a shield cavity, the shield cavity having a first end and a second end and a shield cavity axis;

a deflection rod having a fixed end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the fixed end is secured in the first end of the shield cavity, the free end extends out of the second end of the shield cavity, and the longitudinal axis is aligned with the shield cavity axis;

an gap defined between said deflection rod and said shield, said gap extending from the second end of the shield cavity at least partway along the shield cavity towards the first end of the shield cavity;

said gap being configured to allow bending of the deflection rod within the shield cavity to thereby allow deflection of the free end of the deflection rod away from alignment with the shield cavity axis in response to a load applied to the free end of the deflection rod; and

wherein said deflection of the free end of the deflection rod away from alignment with the shield cavity axis is limited by contact between the deflection rod and the shield.

18. The implant of claim 17 , wherein said deflection rod increases in effective stiffness after an amount of deflection of said free end of the deflection rod.

19. The implant of claim 17 , wherein said deflection rod increases in effective stiffness after about 0.06 inches of deflection of said free end of the deflection rod.

20. The implant of claim 17 , wherein said deflection rod has a first resistance to deflection over a first zone of deflection and a second resistance to deflection over a second zone of further deflection and wherein the second resistance is more than double the first resistance.

21. The implant of claim 17 , wherein said deflection rod has a first resistance to deflection over a first 0.06 inches of deflection and a second resistance to deflection over a further 0.04 inches of deflection and wherein the second resistance is more than double the first resistance.

22. The implant claim 17 , wherein said deflection rod has a first resistance to deflection of about 300 lbs per inch over a first 0.06 inches of deflection and a second resistance to deflection of about 1000 lbs per inch over a further 0.04 inches of deflection.

23. The implant of claim 17 , wherein said gap is an annular gap.

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

a body including a shield with a shield cavity, the shield cavity having a first end and a second end;

a deflection rod having a first end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the first end is secured in the first end of the shield cavity and the free end extends out of the second end of the shield cavity; and

said deflection rod being spaced from said shield along a first portion of said deflection rod extending from the free end and into the shield cavity such that said first portion of said deflection rod is configured for deflection perpendicular to the longitudinal axis in response to a load applied to the free end of the deflection rod, said deflection of said first portion of said deflection rod being limited by the shield.

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

a body including a shield with a shield cavity, the shield cavity having a first end and a second end and a shield cavity axis;

a deflection rod having a first end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the first end is secured in the first end of the shield cavity, the free end extends out of the second end of the shield cavity, and the longitudinal axis is aligned with the shield cavity axis;

an gap defined between said deflection rod and said shield, said gap extending from the second end of the shield cavity at least partway along the shield cavity towards the first end of the shield cavity;

said gap being configured to allow bending of the deflection rod within the shield cavity to thereby allow deflection of the free end of the deflection rod away from alignment with the shield cavity axis in response to a load applied to the free end of the deflection rod; and

wherein said deflection of the free end of the deflection rod away from alignment with the shield cavity axis is limited by contact between the deflection rod and the shield.