Intervertebral stabilizer

1. An intervertebral stabilizer, comprising:

a first surface operable to engage an endplate of a first vertebral bone of a spine;

a second surface spaced apart from the first surface and operable to engage an endplate of an adjacent second vertebral bone of the spine; and

a spring element including a substantially solid exterior wall forming a hollow passage between the first and second surfaces, the solid exterior wall including at least one helical slit therethrough forming a plurality of annular circumferential, overlapping helical coils, the spring element being disposed between the first and second surfaces and operable to provide reactive force in response to compression loads from the first and second vertebral bones, wherein

at least some diameters of respective turns of the helical coils differ such that those of the turns having larger diameters are disposed towards the first and second surfaces and those of the turns having smaller diameters are centrally located between the turns having larger diameters, and

diameters of the hollow passage between the first and second surfaces vary such that larger diameters are disposed towards the first and second surfaces and smaller diameters are centrally located.

2. The intervertebral stabilizer of claim 1 , wherein a cross-sectional profile taken through the spring element is at least partially hourglass shaped.

3. The intervertebral stabilizer of claim 2 , wherein the cross-sectional profile taken through the spring element has a multiple hourglass shape.

4. The intervertebral stabilizer of claim 1 , wherein at least one of:

the first surface includes a peripheral edge that overhangs at least one coil of the spring element; and

the second surface includes a peripheral edge that overhangs at least one coil of the spring element.

5. The intervertebral stabilizer of claim 4 , wherein at least one of:

a first moment arm is defined by a lateral distance between an outer surface of the at least one coil of the spring element and the peripheral edge of the first surface; and

a second moment arm is defined by a lateral distance between the outer surface of the at least one coil of the spring element and the peripheral edge of the second surface.

6. The intervertebral stabilizer of claim 5 , wherein at least one of the moment arms defined by the hourglass shape operates such that:

a compressive force acting on one of the peripheral edges and the other of the first and second surfaces tends to collapse the spring element and full compression of the spring element in response to the compressive force results in adjacent coils engaging one another; and

further compressive force acting on only a portion of the peripheral edge tends to cause the adjacent coils to engage one another and to expand portions of coils on an opposite side of the spring element from the engaged coils.

7. The intervertebral stabilizer of claim 1 , further comprising one or more bone adhesion facilitating elements operable to promote bone adhesion to at least one of the first and second surfaces.

8. The intervertebral stabilizer of claim 7 , wherein the one or more bone adhesion facilitating elements includes at least one of:

one or more spikes extending from at least one of the first and second surfaces for promoting engagement thereof with the associated vertebral bones;

one or more keels extending from at least one of the first and second surfaces for promoting engagement thereof with the associated vertebral bones; and

one or more roughening elements one at least one of the first and second surfaces for promoting engagement thereof with the associated vertebral bones.

9. The intervertebral stabilizer of claim 1 , wherein:

the first surface includes a peripheral edge that overhangs at least one coil of the spring element;

a moment arm is defined by a lateral distance between an outer surface of the at least one coil of the spring element and the peripheral edge of the first surface; and

the passage is sized and shaped to maximize a length of the moment arm.

10. The intervertebral stabilizer of claim 1 , further comprising a membrane disposed in the passage and substantially closing off the passage to inhibit bone growth therethrough.

11. The intervertebral stabilizer of claim 10 , wherein the membrane is formed as an integral element of the hollow body.

12. The intervertebral stabilizer of claim 1 , wherein the surfaces and the spring element are formed as an integral element from the hollow body.

13. An intervertebral stabilizer, comprising:

a first surface operable to engage an endplate of a first vertebral bone of a spine;

a second surface spaced apart from the first surface and operable to engage an endplate of a second vertebral bone of the spine;

a first rigid element; and

first and second spring elements, each having a substantially solid exterior wall forming a hollow passage extending from at least one of the first and second surfaces toward the first rigid element, the solid exterior wall including at least one helical slit therethrough forming a plurality of annular circumferential, overlapping helical coils, the first spring element being disposed between the first rigid element and the first surface, the second spring element being disposed between the first rigid element and the second surface, and each spring element being operable to provide reactive force in response to compression loads from the first and second vertebral bones, wherein

at least some diameters of respective turns of the helical coils of at least one of the first and second spring elements differ such that turns having smaller diameters are centrally located between turns having larger diameters, and

diameters of the hollow passage extending from at least one of the first and second surfaces vary such that larger diameters are disposed towards the first and/or second surfaces and smaller diameters are disposed towards the first rigid element.

14. The intervertebral stabilizer of claim 13 , further comprising:

a second rigid element; and

a third spring element,

wherein the first spring element is disposed between the first rigid element and the first surface, the second spring element is disposed between the first rigid element and the second rigid element, and the third spring element is disposed between the second rigid element and the second surface.

15. The intervertebral stabilizer of claim 13 , wherein at least some diameters of respective turns of the helical coils of both the first and second spring elements differ.

16. The intervertebral stabilizer of claim 15 , wherein those of the turns having larger diameters are disposed towards the first and second surfaces and those of the turns having smaller diameters are centrally located between the turns having larger diameters.

17. The intervertebral stabilizer of claim 13 , wherein a cross-sectional profile taken through at least one of the spring elements is at least partially hourglass shaped.