Bottom-loading bone anchor assemblies

Patent metadata

Field	Value
Publication number	US-9498254-B2
Application number	US-201514735326-A
Country	US
Kind code	B2
Filing date	Jun 10, 2015
Priority date	Mar 14, 2013
Publication date	Nov 22, 2016
Grant date	Nov 22, 2016

Abstract

Bone anchor assemblies are disclosed herein and include bone anchors, receiver members, and closure mechanisms. In one embodiment, a receiver member can be configured to seat a portion of a bone anchor and to receive a spinal fixation element, such as a rod. In an exemplary embodiment, the receiver member is bottom-loading and can include a seat having an opening that can be selectively increased and decreased in size so as to allow a bone anchor to be bottom-loaded. A force can be applied to the receiver member to increase a size of the opening, allowing a portion of the anchor to pass through the opening and into the seat. A closure element can be coupled to the receiver member and can apply a force to decrease a size of the seat and a size of the opening, angularly fixing the receiver member relative to the bone anchor.

First claim

What is claimed is:

1. A bone anchor assembly, comprising:
a bone anchor having a proximal head and a distal threaded portion; and
a receiver member having a proximal portion with opposed arms configured to receive a spinal fixation rod therebetween, the opposed arms of the receiver member defining a U-shaped recess having opposed planar surfaces for seating spinal fixation rods of differing diameters, the opposed planar surfaces extending at an oblique angle relative to a longitudinal axis of the receiver member, the receiver member having a distal portion having a polyaxial seat formed therein and configured to polyaxially seat the proximal head of the bone anchor, and the opposed arms having interior receiver threads, the receiver threads having a major diameter that increases in a distal-to-proximal direction when the opposed arms are parallel to each other, the receiver member having opposed relief slots formed therein, each slot having a first portion that extends parallel to the longitudinal axis of the receiver member and a second portion that is substantially perpendicular to the first portion;
wherein the opposed arms are configured to move toward one another to cause a size of the polyaxial seat to increase and to cause the second portions of the slots to form a crescent shape, and the opposed arms are configured to move away from one another to cause the size of the polyaxial seat to decrease.

2. The bone anchor assembly of claim 1 , wherein the relief slots are configured to allow the opposed arms to move toward and away from one another and to allow the size of the polyaxial seat to increase and decrease.

3. The bone anchor assembly of claim 1 , wherein the opposed relief slots extend proximally from a distal-most end of the receiver member.

4. The bone anchor assembly of claim 2 , wherein the relief slots are substantially T-shaped.

5. The bone anchor assembly of claim 1 , further comprising a closure mechanism configured to mate to the interior receiver threads of the opposed arms and to cause the opposed arms to move away from one another such that the distal portion of the receiver member compress around the proximal head of the bone anchor to prevent removal of the proximal head from the polyaxial seat in the receiver member.

6. The bone anchor assembly of claim 5 , wherein the closure mechanism comprises a threaded set screw having an outer diameter that increases in a distal-to-proximal direction.

7. The bone anchor assembly of claim 1 , wherein an outer diameter of the proximal head of the bone anchor is greater than a size of an opening formed in a distal end of the receiver member and extending into the polyaxial seat.

8. The bone anchor assembly of claim 1 , wherein the polyaxial seat is configured to frictionally engage the proximal head of the bone anchor when the head is seated therein and no closure mechanism is applied to the receiver member.

9. The bone anchor assembly of claim 1 , wherein the receiver member includes opposed flat surfaces formed therein and configured to limit movement of the distal threaded portion of the bone anchor along a single plane of motion.

10. A method for implanting a bone anchor, comprising:
implanting a threaded shank of a bone anchor in bone;
coupling a proximal head of the threaded shank to a receiver member having at least one relief slot formed therein, the slot having a first portion that extends parallel to a longitudinal axis of the receiver member and a second portion that is substantially perpendicular to the first portion, the second portion forming a crescent shape as the head is coupled to the receiver member;
positioning a spinal fixation rod within a u-shaped recess in the receiver member, the u-shaped recess having a plurality of planar surfaces for seating spinal fixation rods of differing diameters;
applying a closure mechanism that includes an inner set screw and an outer set screw to the receiver member;
tightening the outer set screw to cause a distal portion of the receiver member to compress around the proximal head of the bone anchor and thereby lock the receiver member in a fixed position relative to the bone anchor; and
tightening the inner set screw such that it directly contacts the spinal fixation rod to lock the rod in the u-shaped recess.

11. The method of claim 10 , wherein the outer set screw is threaded into a proximal portion of the receiver member.

12. The method of claim 10 , wherein the closure mechanism is tapered such that the closure mechanism causes opposed proximal arms of the receiver member to move away from one another thereby causing the distal portion of the receiver member to compress around the proximal head of the bone anchor.

13. The method of claim 10 , wherein the receiver member is limited to movement within a single plane of motion relative to the bone anchor.

14. A bone anchor system, comprising:
a bone anchor having a proximal head and a distal threaded portion;
a cylindrical spinal fixation rod;
a monolithic receiver member having:
a proximal portion with opposed arms configured to receive the spinal fixation rod therebetween,
the opposed arms of the receiver member defining a U-shaped recess having first and second opposed planar surfaces for seating spinal fixation rods of differing diameters,
the opposed planar surfaces extending at an oblique angle relative to a longitudinal axis of the receiver member and extending from a flat distal surface that is perpendicular to the longitudinal axis of the receiver member,
the opposed arms having interior receiver threads, the receiver threads having a diameter that increases in a distal-to-proximal direction,
opposed T-shaped relief slots formed in the receiver member having a first portion that extends along the longitudinal axis of the receiver member and a second portion that is substantially perpendicular to the first portion, and
the receiver member having a distal portion having a polyaxial seat formed therein and configured to polyaxially seat the proximal head of the bone anchor;

a closure mechanism that includes:
an outer set screw that is tapered such that the outer set screw is configured to cause the opposed arms of the receiver member to move away from one another thereby causing the polyaxial seat of the receiver member to compress around the proximal head of the bone anchor, and
an inner cylindrical set screw that is configured to secure the spinal fixation rod in the monolithic receiver member,

wherein the opposed arms are configured to move toward one another to cause a size of the polyaxial seat to increase, and to cause the second portion of the T-shaped slots to form a crescent shape.

Assignees

• Medos Int Sarl

Inventors

• Spratt Frank
• Klabunde Ralf
• Chandanson Thibault
• Fournier Richard W

Classifications

• 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