Implants and methods for inter-spinous process dynamic stabilization of a spinal motion segment

1. A method for stabilizing a spinal motion segment, comprising:

providing a spacer member including an upper end structured to contact an inferior surface of an upper spinous process and a lower end structured to contact a superior surface of a lower spinous process and including at least flexibly distinctive first and second sections forming an asymmetrical stiffness profile that varies between anterior and posterior sides of said spacer member wherein said anterior side defines the anterior extent of the spacer member and said posterior side defines the posterior extent of the spacer member and wherein said second section is positioned between said first section and said posterior side and wherein the spacer member includes a first lateral side and a second lateral side, each lateral side extending from said upper end to said lower end and said first section extends along said anterior side and said first and second lateral sides and said second section extends along said posterior side and said first and second lateral sides and wherein said anterior side and said posterior side each extends from the upper end to said lower end; and

positioning said spacer member between the upper and lower spinous processes of the spinal motion segment with said first section oriented anteriorly and said second section oriented posteriorly and with said first and second sections movably supporting the upper and lower spinous processes.

2. The method of claim 1 , wherein said spacer member varies the center of rotation for flexion and extension of an upper vertebral body engaged to said upper spinous process relative to a lower vertebral body engaged to said lower spinous process.

3. The method of claim 1 , further comprising positioning each of the upper and lower spinous processes between arms at each of the upper and lower ends of the spacer member.

4. The method of claim 1 , further comprising engaging the spacer member to posterior vertebral elements of the spinal motion segment with a tether.

5. The method of claim 1 , further comprising providing additional spacer members including alternative configurations defined by the positioning of said first section relative to said second section, wherein said first section is less rigid than said second section in each of said additional spacer members.

6. The method of claim 1 , further comprising injecting a first injectable material into a chamber in one of the first and second sections, the injectable material including a modulus of elasticity different from that of the other first or second section.

7. The method of claim 6 , further comprising:

monitoring the stabilization of the spinal motion segment subsequent to the injecting of the first injectable material;

removing the first injectable material from the chamber of the one of the first and second sections; and

injecting a second injectable material flexibly distinctive from the first injectable material and the other of the first and second sections into the chamber to alter the stabilization of the spinal motion segment.

8. The method of claim 7 , wherein the removing and injecting are performed percutaneously.

9. The method of claim 1 , wherein one of the first and second sections is removable from the spacer member.

10. The method of claim 9 , further comprising:

monitoring the stabilization of the spinal motion segment subsequent to the positioning of the spacer member between the upper and lower spinous processes; and

replacing the removable one of the first and second sections with a third section flexibly distinctive from the first and second sections to alter the stabilization of the spinal motion segment.

11. The method of claim 10 , wherein the replacing is performed percutaneously.