Bone anchors with drag features and related methods

Patent metadata

Field	Value
Publication number	US-11026730-B2
Application number	US-201715591608-A
Country	US
Kind code	B2
Filing date	May 10, 2017
Priority date	May 10, 2017
Publication date	Jun 8, 2021
Grant date	Jun 8, 2021

Abstract

Bone anchors and related methods are disclosed herein. In some embodiments, a bone anchor can include a drag interface. Exemplary drag interfaces include (i) friction between a shank and a bushing, (ii) friction between a bushing and a drag ring, (iii) friction generated by a biased saddle, and (iv) combinations of the above. The drag interface can help maintain the relative position between a receiver member and a shank of the bone anchor prior to locking the bone anchor, preventing unintended movement while still allowing free movement when intended by the user. In some embodiments, a bone anchor can include over-rotation blocking features, such as a groove, lip, or protrusion formed on a bushing of the bone anchor. Various other bone anchor features are also disclosed, including high aspect ratio drag rings and compressible drag posts.

First claim

The invention claimed is:

1. A bone anchor, comprising:
a receiver member that defines a cavity and a rod-receiving recess, the receiver member having proximal and distal ends and a central longitudinal axis;
a bushing disposed in the cavity;
a shank having a head portion retained within the bushing and a bone engaging portion that protrudes distally from the receiver member; and
a drag ring that applies a frictional force to the bushing, the drag ring being disposed in a groove formed in the receiver member,
wherein the bushing includes a split configured to allow for radial expansion and compression of the bushing, and
wherein a distal opening of the cavity of the receiver member has a diameter that is less than a maximum diameter of the bushing,
wherein, with the drag ring disposed in the groove, the drag ring is configured to contact the bushing at a point along an outer surface of the bushing at a maximum diameter of the bushing.

2. The bone anchor of claim 1 , wherein the head portion of the shank is rotatable with respect to the bushing and wherein the bushing exerts a frictional force on the head of the shank.

3. The bone anchor of claim 1 , further comprising a fastener configured to be applied to the receiver member to (i) prevent rotation of the head portion of the shank relative to the bushing and (ii) prevent rotation of the bushing relative to the receiver member.

4. The bone anchor of claim 1 , wherein the bushing includes an over-rotation blocking feature.

5. The bone anchor of claim 4 , wherein the blocking feature comprises a lip formed at a proximal end of the bushing, the lip being configured to contact the drag ring to limit rotation of the bushing relative to the receiver member.

6. The bone anchor of claim 5 , wherein the drag ring has a ramped distal-facing surface oriented at an oblique angle to the central longitudinal axis of the receiver member.

7. The bone anchor of claim 6 , wherein the drag ring has a planar proximal-facing surface oriented perpendicular to the central longitudinal axis of the receiver member.

8. The bone anchor of claim 4 , wherein the blocking feature comprises a lip formed at a proximal end of the bushing, the lip being configured to contact the groove of the receiver member to limit rotation of the bushing relative to the receiver member.

9. The bone anchor of claim 1 , further comprising a saddle disposed in the cavity proximal to the bushing, wherein the saddle includes a distal-facing surface with a drag pin extending distally therefrom.

10. The bone anchor of claim 1 , wherein an interior surface of the bushing is configured to exert a frictional drag force against the head of the shank.

11. The bone anchor of claim 1 , wherein the bushing is configured for polyaxial movement within the cavity of the receiver member.

12. A bone anchor, comprising:
a receiver member that defines a cavity and a rod-receiving recess, the receiver member having proximal and distal ends and a central longitudinal axis;
a bushing disposed in the cavity;
a shank having a head portion retained within the bushing and a bone engaging portion that protrudes distally from the receiver member; and
a drag ring disposed in a groove formed in the receiver member that exerts a frictional force against the bushing to resist polyaxial movement between the bushing and the receiver member,
wherein, with the drag ring disposed within the groove, the drag ring applies the frictional force radially to an outer surface of the bushing.

13. The bone anchor of claim 12 , wherein at least a portion of the interior surface of the drag ring has a resting diameter that is less than an external diameter of the bushing.

14. The bone anchor of claim 12 , wherein the drag ring includes one or more teeth that extend radially-inward from a circular main body of the drag ring.

15. The bone anchor of claim 12 , further comprising a saddle positioned within the receiver member.

16. The bone anchor of claim 15 , wherein the drag ring is disposed between the bushing and the saddle.

17. The bone anchor of claim 12 , wherein, with the drag ring disposed in the groove, the drag ring is configured to contact the bushing at a point along the outer surface of the bushing at a maximum diameter of the bushing.

18. The bone anchor of claim 12 , wherein, with the drag ring disposed in the groove, the drag ring applies the frictional force to a convex outer surface of the bushing.

19. The bone anchor of claim 12 , wherein an interior surface of the bushing includes a spherical surface having a resting diameter that is less than a diameter of the head portion of the shank.

20. A bone anchor, comprising:
a receiver member that defines a cavity and a rod-receiving recess, the receiver member having proximal and distal ends and a central longitudinal axis;
a bushing disposed in the cavity;
a shank having a head portion retained within the bushing and a bone engaging portion that protrudes distally from the receiver member; and
a drag ring disposed in a groove formed in the receiver member that exerts a frictional force against the bushing to resist polyaxial movement between the bushing and the receiver member,
wherein the drag ring includes one or more teeth that extend radially-inward from a circular main body of the drag ring.

21. A bone anchor, comprising:
a receiver member that defines a cavity and a rod-receiving recess, the receiver member having proximal and distal ends and a central longitudinal axis;
a bushing disposed in the cavity;
a shank having a head portion retained within the bushing and a bone engaging portion that protrudes distally from the receiver member; and
a drag ring disposed in a groove formed in the receiver member that exerts a frictional force against the bushing to resist polyaxial movement between the bushing and the receiver member,
wherein, with the drag ring disposed in the groove, the drag ring applies the frictional force to a convex outer surface of the bushing.

Assignees

• Medos Int Sarl

Inventors

• Ramsay Christopher
• Hawkins J Riley
• Montello Albert
• Peterson Joseph

Classifications

• A61B17/7037 Primary

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

• A61B17/8605 Primary

  Heads, i.e. proximal ends projecting from bone · CPC title

• A61B17/7032

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

• A61B17/8685

  comprising multiple separate parts · CPC title