Vertebral Interbody cage with translatable locking screw

• US 20030153975A1
• Filed: 02/05/2003
• Published: 08/14/2003
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: Zimmer Biomet Spine, Inc. (Zimvie Incorporated)
• Original Assignee: Cross Medical Products Incorporated (Zimmer Biomet Holdings, Inc.)
• Inventors: Timm, Jens Peter, Byrd, John Abbott III
• Granted Patent: US 7,077,864 B2
• Time in Patent Office: Days
• US Class Current: 623/17.11
• CPC Class Codes: A61F 2/447 substantially parallelepipedal, e.g. having a rectangular or trapezoidal cross-section
• CPC Class Codes: A61F 2/4611 of spinal prostheses
• CPC Class Codes: A61F 2002/2835 Bone graft implants for filling a bony defect or an endoprosthesis cavity, e.g. by synthetic material or biological material
• CPC Class Codes: A61F 2002/30266 wedge-shaped parallelepipeds
• CPC Class Codes: A61F 2002/30593 hollow
• CPC Class Codes: A61F 2002/30774 internally-threaded
• CPC Class Codes: A61F 2002/30777 Oblong apertures
• CPC Class Codes: A61F 2002/30787 inclined obliquely with respect to each other
• CPC Class Codes: A61F 2002/3079 Stepped or enlarged apertures, e.g. having discrete diameter changes
• CPC Class Codes: A61F 2002/30841 Sharp anchoring protrusions for impaction into the bone, e.g. sharp pins, spikes
• CPC Class Codes: A61F 2002/30904 serrated profile, i.e. saw-toothed
• CPC Class Codes: A61F 2230/0082 parallelepipedal
• CPC Class Codes: A61F 2310/00017 Iron- or Fe-based alloys, e.g. stainless steel
• CPC Class Codes: A61F 2310/00023 Titanium or titanium-based alloys, e.g. Ti-Ni alloys
• CPC Class Codes: A61F 2310/00161 Carbon; Graphite
• CPC Class Codes: A61F 2310/00179 Ceramics or ceramic-like structures

Abstract

A vertebral cage is provided for use in preserving the space between adjacent vertebral during the process of spinal fusion. In particular, this cage has an open modified oval peripheral shape with a continuous fluid anterior wall having angled screw passages accessible through co-planar openings to allow the construct to be stabilized between adjacent vertebral bodies through their endwalls. In addition, the cage has a back to front wedge taper with pull-out resistant ratchet surfaces. Further, in a second aspect of the invention, the screw passages have a unique locking mechanism provided by oversized internal threads in combination with a second locking thread on the head of the associated bone screws that allows for axial translation of the screws within the screw passages. This in turn permits play in the angulation of the screw relative to the anchoring bone in order to optimize the screw placement in the bone.

Claims

1. A vertebral cage having a front wall terminating at both lateral sides in a side wall, and a rear wall terminating at both lateral sides, said side walls curving so as to join said lateral sides of said rear wall to provide a single continuous exterior surface, said cage further including a center opening and said front wall including at least two angled screw passages each having an access opening defining a plane co-planar with the exterior surface.

2. A vertebral cage as set forth in claim 1 wherein the front wall, the rear wall and the side walls together define a top edge and a bottom edge each having a high friction surface.

3. A vertebral cage as set forth in claim 2 wherein said high friction surface is a toothed surface.

4. A vertebral cage as set forth in claim 3 wherein said toothed surface is inclined toward the rear wall of the cage.

5. A vertebral cage as set forth in claim 1 wherein the front wall further includes at least one recess for the implantation of the cage.

6. A vertebral cage as set forth in claim 1 wherein the front wall includes three angled passages.

7. A vertebral cage as set forth in claims 6 wherein two of the inferior passages have a longitudinal axis that intersects the center opening toward an inferior direction of the cage and one of the passages have a longitudinal axis that intersects the center opening toward.

8. A vertebral cage as set forth in claim 1 wherein the screw passages include internal threads.

9. An orthopedic implant having an internally threaded to form a female thread recess for a fixation member, and a fixation member having external locking threads to form a mating male thread which correspond to the internal threads, wherein the internal threads and the external thread have the same pitch, but the major diameter of the internal threads is larger than the major diameter of the external threads and the depth of the spiral face of the internal thread is greater than the depth of the spiral face of the external thread so as to permit the axial translation of the fixation member in the passage.

10. An orthopedic implant as set forth in claim 9 wherein the locking thread of the male thread form has a first profile and the locking thread of the female thread form has a second profile and wherein the first profile is substantially smaller than the second profile.

11. An orthopedic implant as set forth in claim 10 wherein the width of the first thread profile is from about 50% to about 85% of the width of the second thread profile.

12. An orthopedic implant as set forth in claim 11 wherein the width of the first thread profile is from about 55% to about 75% of the width of the second thread profile.

13. An orthopedic implant as set forth in claim 12 wherein the width of the first thread profile is from about 60% to about 70% of the width of the second thread profile.

14. An orthopedic implant as set forth in claim 13 wherein the width of the first thread profile is about ⅔

of the width of the second thread profile.

15. An orthopedic implant as set forth in claim 9 wherein the longitudinal distance need to achieve one full rotation of thread spiral is the same for the male and female locking threads.

16. An orthopedic implant as set forth in claim 15 wherein the depth of thread engagement of the male thread is from about 70% to 98% of the depth of the corresponding female thread.

17. An orthopedic implant as set forth in claim 16 wherein the depth of thread engagement of the male thread is from about 80% to 95% of the depth of the corresponding female thread.

18. An orthopedic implant as set forth in claim 17 wherein the depth of thread engagement of the male thread is from about 85% to 95% of the depth of the corresponding female thread.

19. An orthopedic implant as set forth in claim 9 wherein the fixation member has a longitudinal screw area having a first section and a second section, the first section having a cancellous thread with a symmetrical cross sectional shape and a sharp spiral edge, and the second section having a symmetrical trapezoidal cross sectional shape.

20. An orthopedic implant as set forth in claim 19 wherein the second section has a trapezoidal cross sectional shape having a front thrust surface with an angle of from about 40°

to about 80°

.

21. An orthopedic implant as set forth in claim 20 wherein the second section has a trapezoidal cross sectional shape having a front thrust surface with an angle of from about 50°

to about 70°

.

22. An orthopedic implant as set forth in claim 21 wherein the second section has a trapezoidal cross sectional shape having a front thrust surface with an angle of from about 55°

to about 65°

.

23. An orthopedic implant as set forth in claim 22 wherein the transverse plane of the spiral face is flat and less than 0.04 inches deep.

24. An orthopedic implant having an internally threaded recess to form a female thread for a fixation member and a fixation member having external locking threads to form a mating male thread which corresponds to the internal threads;

wherein the external locking threads have a first profile which is smaller than the corresponding second profile of the female locking thread.

25. An orthopedic implant 24 wherein the width of the thread profile is from about 50% to about 85% of the corresponding thread profile of the female thread.

26. An orthopedic implant 25 wherein the width of the thread profile is from about 60% to about 70% of the corresponding thread profile of the female thread.