Expandable interbodies and related methods

1. An expandable interbody comprising: a superior shell having a proximal end and a distal end, the superior shell defining a superior surface extending from the proximal end to the distal end configured to engage an inferior surface of a first vertebral body, the superior shell having two side walls, each of the superior shell side walls having at least one angled channel; an inferior shell having a proximal end and a distal end, the inferior shell defining an inferior surface configured to engage a superior surface of a second vertebral body, the inferior shell having two side walls, each of the inferior shell side walls having at least one angled channel; and a control member comprising interlocking proximal and distal cages and an adjustment screw defining a longitudinal axis, the adjustment screw configured to engage with the proximal and distal cages; wherein the proximal cage comprises at least one superior lateral projection and at least one inferior lateral projection, each lateral projection of the proximal cage configured to engage with one of the angled channels of the superior and inferior shells; wherein the distal cage comprises at least one superior lateral projection and at least one inferior lateral projection, each lateral projection of the distal cage configured to engage with one of the angled channels of the superior and inferior shells, and wherein rotation of the adjustment screw causes the distal cage to move longitudinally relative to the proximal cage, which in turn causes the expandable interbody to expand or contract in a direction transverse to the longitudinal axis.

2. The expandable interbody of claim 1 , wherein the superior and inferior shells each further comprise distal and proximal angled surfaces, and wherein the distal and proximal cages each further comprise superior and inferior angled surfaces that respectively engage with the distal and proximal angled surfaces of the superior and inferior shells.

3. The expandable interbody of claim 2 , wherein at least one of the superior and inferior angled surfaces of the proximal and distal cages defines a rounded surface or a cylindrical-shaped surface so as to achieve a linear point of contact between it and the corresponding distal and proximal angled surface of the superior and/or inferior shell.

4. The expandable interbody of claim 3 , wherein the cylindrical-shaped surface comprises a pin that is secured to the respective cage.

5. The expandable interbody of claim 4 , wherein the pin comprises a material distinct from that of the respective cage to which it is secured.

6. The expandable interbody of claim 5 , wherein the material of the pin is selected to achieve a lower coefficient of friction between it and the superior and/or inferior shells than would be achieved if the material of the pin were identical to that of the respective cage.

7. The expandable interbody of claim 1 , wherein one or more of the superior and inferior lateral projections of the proximal and distal cages comprises a pin secured to the proximal and/or distal cage, wherein at least one end of each pin is configured to slide along one of the angled channels of the superior and inferior shells.

8. The expandable interbody of claim 7 , wherein the pin comprises a material distinct from that of the respective cage to which it is secured.

9. The expandable interbody of claim 8 , wherein the material of the pin is selected to achieve a lower coefficient of friction between it and the corresponding angled channels of the respective superior and/or inferior shells than would be achieved if the material of the pin were identical to that of the respective cage to which it is secured.

10. The expandable interbody of claim 1 , wherein the adjustment screw threadingly engages with the distal cage and is in a fixed longitudinal orientation relative to the proximal cage.

11. The expandable interbody of claim 1 , wherein the adjustment screw threadingly engages with the proximal cage and is in a fixed longitudinal orientation relative to the distal cage.

12. The expandable interbody of claim 1 , wherein the adjustment screw threadingly engages with both the proximal cage and the distal cage.

13. The expandable interbody of claim 1 , wherein the adjustment screw comprises a twin screw having a proximal screw and a distal screw, the proximal screw having a threaded bore open at its distal end and configured to threadingly receive the distal screw.

14. The expandable interbody of claim 1 , wherein both the superior and inferior shells are curved toward each other at their respective distal ends so as to form a bullet-like nose shape that at least partially encloses a distal end of the expandable interbody when in a collapsed configuration.

15. The expandable interbody of claim 1 , wherein—when the expandable interbody is in an expanded configuration—the superior shell, the inferior shell, the proximal cage, and the distal cage each comprise openings therethrough extending from the superior surface of the superior shell to the inferior surface of the inferior shell so as to define a through-channel for bone growth.

16. The expandable interbody of claim 1 , wherein at least one of the superior shell, inferior shell, proximal cage, distal cage, and adjustment screw comprises a porous material.

17. The expandable interbody of claim 16 , wherein the porous material comprises layers of porous sheets that have been diffusion-bonded to form a uniform material.

18. The expandable interbody of claim 1 , wherein the superior surface defines a first plane and the inferior surface defines a second plane that is substantially parallel to the first plane when the expandable interbody is in a collapsed configuration.

19. The expandable interbody of claim 18 , wherein the first plane is substantially parallel to the second plane when the expandable interbody is in an expanded configuration.

20. The expandable interbody of claim 18 , wherein the first plane is not parallel to the second plane when the expandable interbody is in an expanded configuration.