Methods and apparatuses for vertebral body distraction and fusion employing a coaxial screw gear sleeve mechanism

1. A distractible intervertebral body fusion device adapted for implantation into, and fusion of, an intervertebral disc space of a patient, comprising;

a first bearing surface;

a second bearing surface; and

at least one coaxial screw gear sleeve mechanism disposed between the first bearing surface and the second bearing surface, the coaxial screw gear sleeve mechanism including:

a threaded post projecting inwardly from one of the first bearing surface and the second bearing surface; and

a corresponding sleeve having a threaded interior surface surrounding and mating with the threaded post and a helically geared exterior surface;

wherein selective rotation of the sleeve causes an expansion of the first bearing surface relative to the second bearing surface due to a telescoping expansion resulting from the sleeve translating relative to one of the first bearing surface and the second bearing surface simultaneously with the threaded post translating relative to the sleeve,

such that the coaxial screw gear sleeve mechanism is adapted to support in-vivo loads between the first bearing surface and the second bearing surface to maintain a normal height of the disc space following implantation of the device into the intervertebral disc space and during a time fusion occurs between vertebral bodies of the intervertebral disc space of the patient.

2. The device of claim 1 , wherein the geared exterior surface of the sleeve includes a plurality of gear teeth defined on a thread and the thread further includes an end portion comprising a bare thread portion not having gear teeth thereon.

3. The device of claim 2 , further comprising a drive mechanism having a drive thread that interfaces with the geared exterior surface such that rotation of the drive mechanism causes rotation of the sleeve, wherein as the drive mechanism is rotated the gear teeth of the sleeve are sequentially contacted by the drive thread of the drive mechanism to rotate the sleeve relative to the threaded post to expand the first bearing surface and the second bearing surface relative to each other, and wherein the drive thread of the drive mechanism is unable to engage the bare thread portion such that as the drive mechanism advances from the gear teeth to the bare thread portion the drive mechanism is unable to rotate the sleeve to further expand the first bearing surface and the second bearing surface relative to each other.

4. The device of claim 3 , wherein a relative linear distance of a portion of the thread having gear teeth thereon and the end portion comprising the bare thread portion is predetermined to provide a specific predetermined maximum amount of distraction between the first bearing surface and the second bearing surface.

5. The device of claim 2 , wherein the end portion comprising the bare thread portion is adjacent a bottom end of the sleeve that is positioned adjacent one of the first bearing surface and the second bearing surface.

6. The device of claim 1 , wherein an end of at least one of the first bearing surface and the second bearing surface is tapered in a direction transverse to a direction of the expansion.

7. The device of claim 1 , wherein at least one of the first bearing surface and the second bearing surface is angled along a direction transverse to a direction of the expansion.

8. The device of claim 1 , wherein the device includes a pair of coaxial screw gear sleeve mechanisms, and wherein each coaxial screw gear sleeve mechanism is independently rotatable.

9. The device of claim 8 , further comprising a threaded member that engages the coaxial screw gear sleeve mechanisms to selectively rotate the sleeve of each coaxial screw gear sleeve mechanism, the threaded member including a first portion engaging a first of the coaxial screw gear sleeve mechanisms and a second portion engaging a second of the coaxial screw gear sleeve mechanisms, and wherein the first portion and the second portion are independently rotatable relative to each other.

10. The device of claim 1 , wherein the first bearing surface is an outer surface of a first member and the second bearing surface is an outer surface of a second member, and wherein a junction where the threaded post meets an inner surface of the member corresponding to the one of the first bearing surface and the second bearing surface includes a chamfer.

11. The device of claim 1 , wherein at least one of the first bearing surface and the second bearing surface includes an aperture extending through the bearing surface in a direction of the expansion.

12. A size-adjustable implant positionable between adjacent first and second vertebral bodies for fusion of the adjacent first and second vertebral bodies, the implant comprising:

a first member;

a second member;

a coaxial screw gear sleeve mechanism disposed between the first member and the second member, the coaxial screw gear sleeve mechanism including a sleeve having a helical thread with a plurality of gear teeth thereon; and

wherein selective rotation of the sleeve causes an expansion of the first member relative to the second member due to a telescoping expansion of the sleeve translating relative to one of the first member and the second member simultaneously with the other of the first member and the second member translating relative to the sleeve,

such that the coaxial screw gear sleeve mechanism is adapted to support in-vivo loads between the first member and the second member to maintain a normal height of the disc space following implantation of the device into the intervertebral disc space and during a time fusion occurs between vertebral bodies of the intervertebral disc space of the patient.

13. The implant of claim 12 , wherein the thread further includes an end portion comprising a bare thread portion not having gear teeth thereon.

14. The device of claim 13 , further comprising a drive mechanism having a drive thread that interfaces with the gear teeth of the sleeve such that rotation of the drive mechanism causes rotation of the sleeve, wherein as the drive mechanism is rotated the gear teeth of the sleeve are sequentially contacted by the drive thread of the drive mechanism to rotate the sleeve to expand the first member and the second member relative to each other, and wherein the drive thread of the drive mechanism is unable to engage the bare thread portion such that as the drive mechanism advances from the gear teeth to the bare thread portion the drive mechanism is unable to rotate the sleeve to further expand the first member and the second member relative to each other.

15. The device of claim 14 , wherein a relative linear distance of a portion of the thread having gear teeth thereon and the end portion comprising the bare thread portion is predetermined to provide a specific predetermined maximum amount of distraction between the first member and the second member.

16. The device of claim 13 , wherein the end portion comprising the bare thread portion is adjacent a bottom end of the sleeve that is positioned within one of the first member and the second member.

17. The device of claim 12 , wherein an end of at least one of the first member and the second member is tapered in a direction transverse to a direction of the expansion.

18. The device of claim 12 , wherein at least one of the first member and the second member is angled along a direction transverse to a direction of the expansion.

19. The device of claim 12 , wherein the device includes a pair of coaxial screw gear sleeve mechanisms, and wherein each coaxial screw gear sleeve mechanism is independently rotatable.

20. The device of claim 19 , further comprising a threaded member that engages the coaxial screw gear sleeve mechanisms to selectively rotate the sleeve of each coaxial screw gear sleeve mechanism, the threaded member including a first portion engaging a first of the coaxial screw gear sleeve mechanisms and a second portion engaging a second of the coaxial screw gear sleeve mechanisms, and wherein the first portion and the second portion are independently rotatable relative to each other.

21. The device of claim 12 , wherein at least one of the first member and the second member includes an aperture extending through the member in a direction of the expansion.

22. A distractible intervertebral body fusion device adapted for implantation into, and fusion of, an intervertebral disc space of a patient, comprising;

a first bearing surface;

a second bearing surface; and

at least one coaxial screw gear sleeve mechanism disposed between the first bearing surface and the second bearing surface, the coaxial screw gear sleeve mechanism including:

a threaded post projecting inwardly from one of the first bearing surface and the second bearing surface; and

a corresponding sleeve having a threaded interior surface surrounding and mating with the threaded post and a helically geared exterior surface;

wherein selective rotation of the sleeve causes an expansion of the first bearing surface relative to the second bearing surface due to a telescoping expansion resulting from the sleeve translating relative to one of the first bearing surface and the second bearing surface simultaneously with the threaded post translating relative to the sleeve, such that the coaxial screw gear sleeve mechanism is adapted to support in-vivo loads between the first bearing surface and the second bearing surface to maintain a normal height of the disc space following implantation of the device into the intervertebral disc space and during a time fusion occurs between vertebral bodies of the intervertebral disc space of the patient,

wherein the threaded post is unitarily formed with the one of the first bearing surface and the second bearing surface.