Polyaxial pedicle screw with increased angulation

Patent metadata

Field	Value
Publication number	US-9532810-B2
Application number	US-201615041732-A
Country	US
Kind code	B2
Filing date	Feb 11, 2016
Priority date	Mar 9, 2011
Publication date	Jan 3, 2017
Grant date	Jan 3, 2017

Abstract

A polyaxial bone anchor including a housing and a bone screw. A bottom surface of the housing includes an aperture that defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the housing. The aperture is V-shaped, with the V-shape having converging side walls that define a low-angulation direction near their intersection and a high-angulation direction opposite the low-angulation direction. In some cases, the angulation limit of the bone screw is generally constant over a range of azimuthal angles centered around the high-angulation direction. The housing may be modular, including tabs on one component that are plastically deformed to engage a lip on another component. During assembly, a mandrel advances longitudinally along a bore in the housing, and forces the tabs radially outward toward the lip to a radially outward plastically deformed state.

First claim

What is claimed is:

1. A polyaxial bone anchor, comprising:
a housing having an upper end, a lower end and a bore extending through the housing from the upper end to the lower end, the bore opening out at the lower end at a lower opening, the housing including a channel configured for receiving an elongate stabilization member therethrough which extends from a first side surface of the housing to a second side surface of the housing opposite the first side surface transverse to the bore; and
a bone screw including a head and a shank extending from the head, the head of the bone screw positionable in the housing with the shank extending from the lower end of the housing;
wherein the lower opening of the bore defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the bore; and
wherein the lower opening of the bore comprises:
a closed end proximate the longitudinal axis;
an open end distal to the longitudinal axis; and
curved side walls connecting the closed end and the open end and that define a low-angulation direction proximate their intersection at the closed end and that define a high-angulation direction opposite the low-angulation direction.

2. The polyaxial bone anchor of claim 1 , wherein the sidewalls are curved outward so as to be concave.

3. The polyaxial bone anchor of claim 2 , wherein the angulation limit of the bone screw increases monotonically from the low-angulation direction to the high-angulation direction over a range of azimuthal angles centered around the high-angulation direction.

4. The polyaxial bone anchor of claim 3 , wherein the sidewalls are curved such that the minimum angulation limit is located at the closed end in the low-angulation direction.

5. The polyaxial bone anchor of claim 3 , wherein the range of azimuthal angles is greater than 70 degrees, and the angulation limit in the range centered around the high-angulation direction is greater than 35 degrees.

6. The polyaxial bone anchor of claim 3 , wherein the range of azimuthal angles continuously increases from about twenty-five degrees at the low-angulation direction to about forty-seven degrees at the high-angulation direction.

7. The polyaxial bone anchor of claim 1 , wherein the housing comprises an upper housing and a lower housing rotatably coupled to the upper housing, the lower housing including the lower opening of the bore.

8. The polyaxial bone anchor of claim 7 , wherein the housing is configured to provide limited rotational movement between the upper housing and lower housing through less than 360 degrees.

9. The polyaxial bone anchor of claim 8 , wherein one of the upper housing and the lower housing includes a groove and the other of the upper housing and the lower housing includes a protuberance, the groove having a first end surface and a second end surface and the protuberance traveling in the groove between the first end surface and the second end surface, wherein rotation between the upper housing and the lower housing is limited by the protuberance contacting either the first end surface of the groove or the second end surface of the groove.

10. The polyaxial bone anchor of claim 9 , wherein the protuberance travels in the groove through at least 180 degrees, but less than 360 degrees.

11. The polyaxial bone anchor of claim 1 , wherein the lower end of the housing comprises a generally spherical surface; and wherein the lower opening of the bore comprises an aperture in the generally spherical surface, wherein the aperture extends uniformly through the lower end of the housing in a direction of the longitudinal axis.

12. The polyaxial bone anchor of claim 11 , wherein proximate the high-angulation direction, the aperture comprises an intersection of the generally spherical surface with a plane perpendicular to the longitudinal axis of the bore.

13. The polyaxial bone anchor of claim 11 , wherein proximate the high-angulation direction, the aperture further extends along a lateral side of the housing to form an increased notch that increases the high-angulation direction.

14. The polyaxial bone anchor of claim 1 , wherein the sidewalls have an irregular curvature.

15. The polyaxial bone anchor of claim 1 , wherein the sidewalls are curved inward so as to be convex.

16. The polyaxial bone anchor of claim 1 , wherein the lower opening of the bore is left-right symmetric about a plane that includes the longitudinal axis of the bore.

17. The polyaxial bone anchor of claim 1 , wherein the housing is a unitary structure.

18. A polyaxial bone anchor, comprising:
a housing having an upper end, a lower end and a bore extending through the housing from the upper end to the lower end along a longitudinal axis, the bore opening out at the lower end at a lower opening, the housing including a channel configured for receiving an elongate stabilization member therethrough which extends from a first side surface of the housing to a second side surface of the housing opposite the first side surface transverse to the bore; and
a bone screw including a head and a shank extending from the head, the head of the bone screw positionable in the housing with the shank extending from the lower end of the housing;
wherein the lower opening of the bore includes a single pair of opposing side walls having a bowed V-shape that defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the bore;
wherein the side walls are spaced further apart from each other via a first arcuate end wall away from the longitudinal axis to define a maximum value of the angulation limit in a high-angulation direction; and
wherein the side walls are spaced closer to each other via a second arcuate end wall nearer the longitudinal axis to define a minimum value of the angulation limit in a low-angulation direction.

19. The polyaxial bone anchor of claim 18 , wherein the sidewalls are curved outward so as to be concave.

20. The polyaxial bone anchor of claim 19 , wherein the angulation limit of the bone screw increases monotonically from the low-angulation direction to the high-angulation direction.

21. The polyaxial bone anchor of claim 19 , wherein the range of azimuthal angles continuously increases from about twenty-five degrees at the low-angulation direction to about forty-seven degrees at the high-angulation direction.

Assignees

• Zimmer Spine Inc

Inventors

• Hestad Hugh D
• Dant Jack A
• Lundequam Eric J
• Jerke Eric P
• Hoch Deborah Lynn

Classifications

• A61B17/7038 Primary

  to a different extent in different directions, e.g. within one plane only · CPC title

• A61B17/7037

  wherein pivoting is blocked when the rod is clamped · CPC title

• Y10T29/49863

  with prestressing of part · CPC title

• A61B17/7032

  Screws or hooks with U-shaped head or back through which longitudinal rods pass · CPC title