Bone anchor assemblies and methods with improved locking

Patent metadata

Field	Value
Publication number	US-9918747-B2
Application number	US-201514966531-A
Country	US
Kind code	B2
Filing date	Dec 11, 2015
Priority date	Mar 14, 2013
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

Various exemplary methods and devices are provided for fixing bone anchors to bone. In general, the methods and devices can allow for a bone anchor to be fixed to a bone at a desired angle to a receiver member. In an exemplary embodiment, a bone anchor assembly is provided that includes a bone anchor configured to engage bone, a receiver member that polyaxially seats a spherical head of the bone anchor, and a compression member seated within the receiver member, proximally of the head of the bone anchor. The compression member can have a distal end with gripping features thereon configured to create at least one line contact and/or one band contact with the head of the bone anchor, thus providing a firm grip on the head of the bone anchor and reducing a risk of slippage of the bone anchor with respect to the receiver member.

First claim

What is claimed is:

1. A bone anchor assembly, comprising:
a bone anchor having a proximal head portion and a distal shank portion;
a receiver member having a polyaxial seat formed therein for polyaxially seating the head portion of the bone anchor; and
a compression member configured to be disposed within the receiver member, the compression member having an inner sidewall surface and a concentric outer sidewall surface connected by a spherically shaped distal-facing surface that extends from the inner sidewall surface to a distal-most end surface of the compression member;
wherein a proximal portion of the compression member includes a pair of spaced apart arms defining a U-shaped seat for receiving a spinal fixation element;
wherein the spherically shaped distal-facing surface includes a tooth formed thereon and disposed between a first intersection of the inner sidewall surface and the distal-facing surface and a second intersection of the distal-most end surface and the distal-facing surface;
wherein the tooth extends around an entire circumference of the distal-facing surface such that a crest of the tooth is configured to make a ring-shaped line contact with the head portion of the bone anchor; and
wherein a distal-most portion of the outer sidewall surface defines a continuous cylinder having a single diameter.

2. The bone anchor assembly of claim 1 , wherein the tooth extends around the entire circumference of the distal-facing surface of the compression member in a plane that is perpendicular to a longitudinal axis of the compression member.

3. The bone anchor assembly of claim 1 , wherein the tooth extends around the entire circumference of the distal-facing surface of the compression member in a plane that is at a non-perpendicular angle to a longitudinal axis of the compression member.

4. The bone anchor assembly of claim 1 , wherein the outer sidewall surface and the inner sidewall surface are cylindrically shaped.

5. The bone anchor assembly of claim 1 , wherein the distal-facing surface is shaped as a negative of the proximal head portion of the bone anchor.

6. The bone anchor assembly of claim 1 , wherein a largest diameter of the crest of the tooth is smaller than a diameter of the proximal head portion of the bone anchor.

7. The bone anchor assembly of claim 1 , wherein the tooth includes two planar, substantially perpendicular sidewalls that meet at the crest.

8. The bone anchor assembly of claim 1 , wherein the tooth is the only feature formed on the distal-facing surface.

9. The bone anchor assembly of claim 1 , further comprising a set screw having an outer thread configured to engage an inner thread formed on the receiver member such that the set screw can contact a proximal portion of the compression member as it is threaded into the receiver member.

10. The bone anchor assembly of claim 9 , wherein the set screw includes a central passage from a top surface thereof to a bottom surface thereof, the central passage including an inner thread configured to engage an outer thread of a second set screw.

11. A bone anchor assembly, comprising:
a bone anchor having a proximal head portion and a distal shank portion;
a receiver member having a polyaxial seat formed therein for polyaxially seating the head portion of the bone anchor; and
a compression member configured to be disposed within the receiver member, the compression member having an inner sidewall surface and a concentric outer sidewall surface connected by a distal-facing surface that is shaped as a negative of the proximal head portion of the bone anchor and extends from the inner sidewall surface to a distal-most end surface of the compression member;
wherein a proximal portion of the compression member includes a pair of spaced apart arms defining a U-shaped seat for receiving a spinal fixation element;
wherein the distal-facing surface includes a gripping feature formed thereon and disposed between a first intersection of the inner sidewall surface and the distal-facing surface and a second intersection of the distal-most end surface and the distal-facing surface;
wherein the gripping feature is configured to grip the proximal head portion of the bone anchor with greater friction as compared to the distal-facing surface formed as a negative of the proximal head portion of the bone anchor; and
wherein a distal-most portion of the outer sidewall surface has a first maximum diameter and a proximal-most portion of the outer sidewall surface has a second maximum diameter that is larger than the first maximum diameter.

12. The bone anchor assembly of claim 11 , wherein the gripping feature extends around an entire circumference of the distal-facing surface of the compression member.

13. The bone anchor assembly of claim 12 , wherein the gripping feature extends around the entire circumference of the distal-facing surface of the compression member in a plane that is perpendicular to a longitudinal axis of the compression member.

14. The bone anchor assembly of claim 12 , wherein the gripping feature extends around the entire circumference of the distal-facing surface of the compression member in a plane that is at a non-perpendicular angle to a longitudinal axis of the compression member.

15. The bone anchor assembly of claim 11 , wherein the outer sidewall surface and the inner sidewall surface are cylindrically shaped.

16. The bone anchor assembly of claim 11 , wherein the distal-facing surface is spherically shaped.

17. The bone anchor assembly of claim 11 , wherein the gripping feature is the only feature formed on the distal-facing surface.

18. A bone anchor assembly, comprising:
a bone anchor having a proximal spherically-shaped head portion and a distal shank portion;
a receiver member having a polyaxial seat formed therein for polyaxially seating the head portion of the bone anchor; and
a compression member configured to be disposed within the receiver member, the compression member having an inner sidewall surface and a concentric outer sidewall surface connected by a distal-facing spherically-shaped surface that extends from the inner sidewall surface to a distal-most end surface of the compression member;
wherein a proximal portion of the compression member includes a pair of spaced apart arms defining a U-shaped seat for receiving a spinal fixation element;
wherein the distal-facing spherically-shaped surface includes a single tooth formed thereon and extending from the distal-facing spherically-shaped surface at a location spaced apart from a first intersection between the inner sidewall surface and the distal-facing surface and a second intersection between the distal-most end surface and the distal-facing surface;
wherein the single tooth extends around an entire circumference of the distal-facing surface such that a crest of the tooth is configured to make a ring-shaped line contact with the head portion of the bone anchor; and
wherein the pair of spaced apart arms of the compression member each includes a bore formed therein that aligns with a bore formed in a proximally-extending arm of the receiver member when the compression member is disposed within the receiver member.

Assignees

• Depuy Synthes Products Inc

Inventors

• Spratt Frank
• Cormier Philip A
• Quintanilha Ernest
• Dziedzic Sara
• Pavento Nicholas
• SHAW Derek
• Chandanson Thibault

Classifications

• A61B17/7035

  Screws or hooks, wherein a rod-clamping part and a bone-anchoring part can pivot relative to each other · CPC title

• A61B2090/037

  with a frangible part, e.g. by reduced diameter · CPC title

• A61B17/7037 Primary

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

• A61B17/7032 Primary

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