Constrained motion bone screw assembly

Patent metadata

Field	Value
Publication number	US-9795416-B2
Application number	US-201514754259-A
Country	US
Kind code	B2
Filing date	Jun 29, 2015
Priority date	Mar 4, 2005
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

A bone screw assembly includes an anchor portion and a head portion, such as a rod-receiving portion, movably mounted to the anchor portion to allow for controlled angulation between the anchor portion and the head portion. The anchor portion is pivotable in one or more selected directions about an axis relative to the head portion. A restriction member, which may be a rod seat, prevents the anchor portion from pivoting in one or more different directions about another axis relative to the head portion and/or a spinal fixation element received in the head portion. The restriction member may be inserted in the head portion to control direction that the anchor portion pivots relative to the head portion. The restriction member may also serve as a compression member and/or rod seat for seating a spinal rod coupled to the bone screw assembly.

First claim

The invention claimed is:

1. A bone anchor assembly comprising:
a bone anchor having a proximal head and a distal shaft configured to engage bone, the distal shaft having a central longitudinal axis, the proximal head having two opposed flat side surfaces oriented parallel to the longitudinal axis of the distal shaft and two curved surfaces each interposed between the flat side surfaces;
a receiving member having a proximal end and a distal end, the proximal end having two spaced apart upright arm defining a recess for receiving a spinal rod therebetween, the distal end having a bore therethrough, the bore having a proximal opening at the recess and a distal opening sized to allow insertion of the proximal head of the bone anchor therethrough;
a cap having a proximal portion configured to receive the spinal rod, and a distal portion having a distal-most end configured to seat the proximal head such that the distal-most end is positioned circumferentially along the entire curved surfaces of the proximal head, and opposite first and second curved side surfaces of the cap terminating at the distal-most end; and
first and second protrusions having proximal and distal ends and configured to extend distally from the cap on opposite third and fourth sides of the cap such that inner surfaces of the first and second protrusions extend distally beyond the distal-most end of the cap and align with the flat side surfaces of the proximal head.

2. The bone anchor assembly of claim 1 , wherein the cap is positioned about the bone anchor to retain the bone anchor within the receiving member.

3. The bone anchor assembly of claim 1 , wherein the proximal portion of the cap has a U-shaped profile in cross section to provide a seat for receiving the spinal rod.

4. The bone anchor assembly of claim 1 , further comprising a closure mechanism configured to engage with inner surfaces of the arms of the receiving member to secure a spinal rod within the recess.

5. The bone anchor assembly of claim 4 , wherein the closure mechanism is a set screw having an external thread for engaging a thread disposed on the inner surfaces of the arms of the receiving member.

6. The bone anchor assembly of claim 1 , wherein at least one of the first and second protrusions is formed integrally with the cap.

7. The bone anchor assembly of claim 1 , wherein the first and second protrusions are separate elements coupled to the cap.

8. The bone anchor assembly of claim 1 , wherein the first and second protrusions restrict movement of the distal shaft in at least one direction.

9. The bone anchor assembly of claim 1 , wherein the bone anchor is rotatable only about a rotation axis that intersects the flat side surfaces and is oriented perpendicular to the flat side surfaces.

10. The bone anchor assembly of claim 1 , wherein the first and second protrusions prevent the bone anchor from rotation about an axis through a plane that is parallel to the flat side surfaces of the proximal head and the first and second protrusions.

11. The bone anchor assembly of claim 1 , wherein the inner surfaces of the first and second protrusions are each configured to mate with one of the flat side surfaces of the proximal head.

Assignees

• Medos Int Sarl
• Medos Int Sárl

Inventors

• Chao Nam T
• Siu Simon
• Sacher Ronald
• Gurley Jerold P
• Betz Randal
• Newton Peter O

Classifications

• A61B17/7032

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

• A61B17/7037 Primary

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

• A61B17/7041

  with single longitudinal rod offset laterally from single row of screws or hooks (A61B17/7044 takes precedence) · CPC title

• A61B17/704

  the longitudinal element passing through a ball-joint in the screw head · CPC title

• A61B17/7038

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