Polyaxial pedicle screw

Patent metadata

Field	Value
Publication number	US-9198695-B2
Application number	US-201313778684-A
Country	US
Kind code	B2
Filing date	Feb 27, 2013
Priority date	Aug 30, 2010
Publication date	Dec 1, 2015
Grant date	Dec 1, 2015

Abstract

A polyaxial bone anchor including a housing, a bone screw, and a retainer for pivotably coupling the head of the bone screw to the housing. The retainer is positioned into the bore of the housing and includes a plurality of alternating tabs and slots circumferentially arranged to define a cavity for receiving the head portion of the bone screw therein. The retainer is axially moveable in the housing from a first position in which the head portion is not passable through the lower opening of the retainer to a second position in which the head portion is passable through the lower opening of the retainer.

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;
a retainer configured to be positioned into the bore of the housing and having an outermost diameter greater than a diameter of the lower opening, the retainer including a plurality of alternating tabs and first slots circumferentially arranged to define a cavity therein;
a bone screw including a head portion and a shank extending from the head portion, the head portion of the bone screw positionable in the cavity of the retainer with the shank extending from the lower end of the housing by deflecting the tabs radially outward to enlarge a lower opening of the retainer into the cavity from a diameter less than a diameter of the head portion to a diameter greater than or equal to the diameter of the head portion; and
wherein a portion of the retainer includes one or more circumferential or helical second slots formed therein configured for applying a force to move and bias the retainer toward the lower end of the housing while the retainer is positioned in the bore, wherein the one or more circumferential or helical second slots extend transverse to the bore.

2. The polyaxial bone anchor of claim 1 , wherein the retainer is moved toward the upper end of the housing while being positioned in the bore in order to insert the head portion of the bone screw into the cavity of the retainer.

3. The polyaxial bone anchor of claim 2 , wherein the retainer is insertable into the bore of the housing without the head portion of the bone screw positioned in the cavity of the retainer, yet with the head portion of the bone screw positioned in the cavity of the retainer, the retainer is prevented from being removed from the bore of the housing.

4. The polyaxial bone anchor of claim 1 , further comprising a spacer axially movable relative to the retainer, the spacer including a first portion extending from the retainer toward the upper end of the housing which is configured to engage an elongate stabilization member disposed in the channel of the housing and a second portion extending into a bore of the retainer which is configured to engage the head portion of the bone screw.

5. The polyaxial bone anchor of claim 1 , wherein the housing includes an annular rim defining the lower opening, wherein the diameter of the lower opening at the annular rim is less than a diameter of the bore of the housing toward the upper end of the housing from the annular rim.

6. The polyaxial bone anchor of claim 5 , wherein the retainer includes a lower beveled surface which contacts the annular rim of the housing, thereby preventing the tabs of the retainer from deflecting radially outward in order to secure the head portion of the bone screw in the cavity of the retainer.

7. The polyaxial bone anchor of claim 1 , wherein an upper portion of the retainer includes first and second legs defining a channel therebetween aligned with the channel of the housing for receiving an elongate stabilization member therethrough.

8. The polyaxial bone anchor of claim 1 , wherein the retainer has an outermost diameter greater than a diameter of the lower opening and is insertable into the bore of the housing from the lower end of the housing by passing the retainer through the lower opening with the plurality of tabs deflected radially inward.

9. The polyaxial bone anchor of claim 1 , wherein the retainer is movable in the bore of the housing between a first position and a second position, the retainer being closer to the lower end of the housing in the first position and closer to the upper end of the housing in the second position, wherein the head portion of the bone screw is insertable into the cavity of the retainer from the lower end of the housing when the retainer is in the second position, but is not removable from the cavity of the retainer when the retainer is in the first position.

10. The polyaxial bone anchor of claim 9 , wherein the one or more circumferential or helical second slots define a resilient spring biasing the retainer toward the first position.

11. The polyaxial bone anchor of claim 10 , wherein during insertion of the head portion of the bone screw into the cavity of the retainer, the head portion of the bone screw exerts a force against the retainer to move the retainer to the second position.

12. The polyaxial bone anchor of claim 9 , wherein an annular rim defining the lower opening of the housing contacts a lower beveled surface of the retainer to prevent radially outward deflection of a plurality of tabs of the retainer in order to secure the head portion of the bone screw in the cavity of the retainer.

13. A method of assembling a polyaxial bone anchor comprising:
inserting a retainer into a bore of a housing from a lower end of the housing by passing the retainer through the lower opening, the housing having an upper 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, the retainer having an outermost diameter greater than a diameter of the lower opening, the retainer including a plurality of alternating tabs and first slots formed therein providing the retainer with sufficient flexibility to be urged through the lower opening from the lower end of the housing by radially compressing the retainer;
inserting a head portion of a bone screw into a cavity of the retainer from the lower end of the housing by moving the retainer toward the upper end of the housing allowing the plurality of tabs to splay radially outward to accommodate passage of the head portion of the bone screw into the cavity of the retainer; and
urging the retainer, with the head portion of the bone screw positioned in the cavity of the retainer, back toward the lower end of the housing to retain the head portion of the bone screw in the cavity of the retainer;
wherein the retainer is biased toward the lower end of the housing by a biasing spring formed by one or more circumferential or helical second slots in the retainer, wherein the second slots extend transverse to the bore.

14. The method of claim 13 , wherein an annular rim defining the lower opening of the housing contacts a lower beveled surface of the retainer to prevent radially outward deflection of the plurality of tabs of the retainer in order to secure the head portion of the bone screw in the cavity of the retainer.

15. The method of claim 14 , wherein the head portion of the bone screw is not removable from the cavity of the retainer when the retainer is moved toward the lower end of the housing.

Assignees

• Zimmer Spine Inc

Inventors

• Shluzas Alan E
• Hestad Hugh D

Classifications

• A61B17/7035 Primary

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

• A61B17/7032 Primary

  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

• A61B17/7001

  Screws or hooks combined with longitudinal elements which do not contact vertebrae (A61B17/7058 takes precedence) · CPC title

• A61B17/70

  Spinal positioners or stabilisers, e.g. stabilisers comprising fluid filler in an implant · CPC title