Method of providing spinal interbody fusion

1. A method of providing spinal interbody fusion, comprising the steps of:

accessing the intradiscal space between two generally opposed upper and lower vertebral bodies;

placing an access channel adjacent said vertebral bodies in communication with said intradiscal space;

removing nucleus material from said intradiscal space through said access channel;

inserting through said access channel and into said intradiscal space an expandable implant, said implant having an upper contact surface engaging the lower surface of said upper vertebral body, a lower contact surface engaging the upper surface of said lower vertebral body and an expandable intermediate structure therebetween, said expandable intermediate structure capable during expansion of moving said upper contact surface and said lower contact surface apart in a direction along the axis of said spine while maintaining said upper contact surface and said lower contact surface in a relatively fixed position against the respective verterbral bodies;

expanding said expandable implant within said intradiscal space by expanding said intermediate structure to move said upper contact surface and said lower contact surface to thereby distract and support said vertebral bodies along the axis of said spine; and

monitoring the tension in the annulus of the disc between said vertebral bodies during the expansion as an indication of stability of said vertebral bodies and then ending the expansion of said expandable structure upon substantial achievement of said stability.

2. The method of claim 1 , wherein said access channel is expandable and wherein after placing said access channel, said channel is expanded to provide an increased opening through said channel.

3. The method of claim 1 , further comprising an inserter releasably coupled to said expandable structure, said inserter being configured for insertion through said access channel and remaining coupled during expansion of said intermediate structure and released upon completion of expansion of said intermediate structure.

4. The method of claim 1 , wherein said expandable structure comprises a top element including said upper contact surface and a bottom element including said lower contact surface, said top element and said bottom element being movable relatively apart from each other substantially only along the axis of the spine during expansion of said expandable structure.

5. The method of claim 4 , wherein said expandable intermediate structure comprises a plurality of intermediate elements each configured to be movably supported by said inserter and slidably received between said top element and said bottom element and upon such receipt causing said movement of said top element and said bottom element.

6. The method of claim 5 , wherein said top element and said bottom element are initially jointly introduced into said intradiscal space and said intermediate elements are then sequentially introduced individually between said top element then said bottom element.

7. The method of claim 6 , wherein said bottom element is releasably coupled to said inserter and said plurality of said intermediate elements are introduced one intermediate element beneath the other.

8. The method of claim 7 , wherein a preceding intermediate element is held in a position substantially preventing movement in the direction of introduction while a subsequent intermediate element is introduced beneath said preceding intermediate element.

9. The method of claim 8 , wherein said intermediate elements each comprise cooperative constraints therebetween allowing slidable insertion relative to each other during introduction and interlocking engagement therebetween upon completion of said introduction.

10. The method of claim 4 , further comprising the step of introducing through said access channel a filler material comprising a fusion promoting composition into said intradiscal space.

11. The method of claim 10 , wherein said top element, said bottom element and said intermediate structure each have at least one hole, said holes being in communication and wherein said filler material is introduced into said holes.

12. A method of providing spinal interbody fusion, comprising the steps of:

accessing the intradiscal space between two generally opposed upper and lower vertebral bodies, said intradiscal space containing nucleus material within an outer disc annulus;

removing nucleus material from said intradiscal space;

inserting into said intradiscal space an expandable implant, said implant having an upper contact surface engaging the lower surface of said upper vertebral body, a lower contact surface engaging the upper surface of said lower vertebral body and an expandable intermediate structure therebetween, said expandable intermediate structure capable during expansion of gradually moving said upper surface and said lower contact surface apart along the axis of said spine a sufficient distance to cause gradual tension in said disc annulus while maintaining said upper contact surface and said lower contact surface in a relatively fixed position against the respective verterbral bodies;

expanding said expandable implant within said intradiscal space by expanding said intermediate structure to move said upper contact surface and said lower contact surface to thereby distract and support said vertebral bodies along the axis of said spine;

monitoring the tension in the annulus of the disc as an indication of stability of said vertebral bodies;

determining based on the tension in said annulus whether substantial stability of said vertebral bodies has been achieved; and

then ending the expansion of said expandable structure upon substantial achievement of said stability.

13. The method of claim 12 , further comprising the step of placing an access channel adjacent said vertebral bodies in communication with said intradiscal space.

14. The method of claim 13 , further comprising the step of inserting said expandable implant into said intradiscal space through said access channel.

15. The method of claim 13 , wherein said access channel is expandable, and wherein said access channel is expanded prior to insertion of said expandable implant.

16. The method of claim 13 , further comprising an inserter releasably coupled to said expandable structure, said inserter being configured for insertion through said access channel and remaining coupled during expansion of said intermediate structure and released upon completion of expansion of said intermediate structure.

17. The method of claim 12 , wherein said expandable structure comprises a top element including said upper contact surface and a bottom element including said lower contact surface, said top element and said bottom element being movable relatively apart from each other substantially only along the axis of the spine during expansion of said expandable structure.

18. The method of claim 17 , wherein said top element comprises a radiopaque marker and said bottom element comprises a radiopaque marker to enable fluoroscope visualization of the movement of said top element and said bottom element during expansion of said implant along the axis of said spine.

19. The method of claim 17 , wherein said top element, said bottom element and said intermediate structure each have at least one hole for flow therethrough of filler material, said implant further having a filler material receiving orifice defining a pathway into said implant, all of such holes and said orifice being in fluid communication, and further comprising the step of introducing filler material comprising a fusion promoting composition into said orifice to said holes after ending said expansion step.

20. The method of claim 19 , further comprising an injection channel for introducing said filler material into said implant filler receiving orifice, said injection channel being configured for passing through said access channel.