Polyaxial bone fixation element

Patent metadata

Field	Value
Publication number	US-10136923-B2
Application number	US-201615254382-A
Country	US
Kind code	B2
Filing date	Sep 1, 2016
Priority date	Jul 20, 2007
Publication date	Nov 27, 2018
Grant date	Nov 27, 2018

Abstract

The present disclosure includes a polyaxial bone fixation element for use in spinal fixation to interconnect a longitudinal spinal rod with a patient's vertebra. The polyaxial bone fixation element preferably includes a bone anchor, a collet, a body, and a locking cap. The polyaxial bone fixation element preferably enables in-situ assembly. That is, the polyaxial bone fixation element is preferably configured so that in use, the bone anchor may be secured to the patient's vertebra prior to being received within the body. Accordingly, the polyaxial bone fixation element enables a surgeon to implant the bone anchor without the body to maximize visibility and access around the anchoring site. Once the bone anchor has been secured to the patient's vertebra, the body can be snapped-onto the bone anchor. The bone anchor preferably also includes a second tool interface so that a surgical instrument can be directly coupled to the bone anchor.

First claim

What is claimed:

1. An assembly configured to couple a spinal rod to a vertebra, the assembly comprising:
a body that is elongate along a first longitudinal axis, the body including an upper end that defines an upper opening, a lower end that defines a lower opening, a bore that extends between the upper opening and the lower opening along the longitudinal axis, the bore defining a rod-receiving channel configured to receive the spinal rod, the rod-receiving channel disposed along a channel axis that is oriented substantially perpendicular to the longitudinal axis, the bore at least partially defined by a first curved surface that forms a first spherical undercut having a first body diameter, and the bore at least partially defined by a second curved surface that forms a second spherical undercut having a second body diameter that is larger than the first body diameter, the first curved surface positioned closer to the lower opening with respect to a direction parallel to the longitudinal axis than the second curved surface is to the lower opening with respect to the direction, the body further including a collet retention feature positioned at a fixed location between the upper opening and the second curved surface such that the collet retention feature is configured to inhibit movement of a collet that is between the collet retention feature and the lower opening from passing through the upper opening, the collet retention feature defining a retention opening having a third body diameter, and the lower opening defining a fourth body diameter; and
a bone anchor that is elongate along a second longitudinal axis, the bone anchor including a head portion, a shaft portion, and a neck portion positioned between the head portion and the shaft portion, the head portion defining a first screw diameter measured perpendicular to the second longitudinal axis, the shaft portion defining a second screw diameter measured perpendicular to the second longitudinal axis, and the neck portion defining a third screw diameter perpendicular to the second longitudinal axis,
wherein the third screw diameter is less than both the first screw diameter and the second screw diameter, the first screw diameter is less than both the first body diameter and the second body diameter, and the third body diameter is greater than the fourth body diameter and less than the second body diameter.

2. The assembly of claim 1 , wherein the head portion includes a first tool interface configured to engage a first surgical instrument, and the head portion includes a second tool interface configured to engage a second surgical instrument, the first tool interface and the second tool interface positioned in a head interface cavity.

3. The assembly of claim 2 , wherein the first tool interface includes a drive surface which is an internal surface formed in the head portion of the bone anchor, the first tool interface is configured to receive an external tip of the first surgical instrument, and the second tool interface includes a plurality of threads formed on the head portion, the plurality of threads configured to threadedly engage a portion of the second surgical instrument.

4. The assembly of claim 2 , wherein the second tool interface is located proximal of the first tool interface so that the second tool interface does not obstruct access to the first tool interface.

5. The assembly of claim 2 , further comprising:
a collet defining a cavity configured to receive the head portion of the bone anchor, the collet including a portion that is expandable and configured to facilitate entry of the head portion of the bone anchor into the cavity; and
a locking cap removably engageable with the body such that the locking cap is movable from an unlocked position to a locked position, wherein movement of the locking cap from the unlocked position to the locked position urges the spinal rod against the collet to secure the bone anchor relative to the body.

6. The assembly of claim 2 , further comprising the first surgical tool and the second surgical tool.

7. The assembly of claim 1 , further comprising the collet, the collet defining a cavity configured to receive the head portion of the bone anchor, and the collet including a portion that is expandable and configured to facilitate entry of the head portion of the bone anchor into the cavity.

8. The assembly of claim 7 , wherein the collet retention feature contacts a bottom end of a groove in the collet in the loading position to align the flexible arms with the second spherical undercut.

9. The assembly of claim 7 , wherein the body includes one or more partial passageways formed therein so that once the collet has been received within the bore of the body, the body is configured to receive a force applied to the one or more partial passageways that deforms the one or more partial passageways into one or more dimples that extend into the bore of the body, and the one or more dimples comprise the collet retention feature.

10. The assembly of claim 9 , wherein the one or more dimples interact with the collet to inhibit the collet from moving back through the upper opening formed in the body.

11. The assembly of claim 7 , wherein the collet is configured to move within the bore along the longitudinal axis from a loading position to a locked position, when the collet is in the loading position the head portion of the bone anchor is movable within the cavity relative to the collet, and when the collet is in the locked position the head portion of the bone anchor is unable to move within the cavity relative to the collet.

12. The assembly of claim 11 , wherein the collet includes a first end, a second end and at least two slots extending from the second end, the at least two slots defining flexible arms that each have a root end, a terminal end and an outer curvate convex surface proximate the terminal end, wherein the flexible arms are positioned proximate the second curved surface in the loading position, and at least a portion of the outer curvate convex surface of the flexible arms are in line contact with at least a portion of the first curved surface in the locked position.

13. The assembly of claim 7 , wherein the first curved surface defines a first radius of curvature as measured in a plane, the portion of the collet that is expandable includes an outer collet surface configured to abut the first curved surface, the outer collet surface defines a second radius of curvature as measured in the plane, and the first radius of curvature is different than the second radius of curvature.

14. The assembly of claim 1 , wherein the rod-receiving channel extends from the upper end toward the lower end.

15. The assembly of claim 1 , wherein the upper opening of the body defines a fifth body diameter that is larger than the first body diameter, and smaller than the second body diameter.

16. The assembly of claim 1 , further comprising a set screw and a saddle, the set screw configured to threadedly engage with the upper end of the body, the saddle coupled to the set screw such that the set screw is free to rotate with respect to the saddle.

17. The assembly of claim 16 , wherein one of the set screw and the saddle includes a stem, and the other of the set screw and the saddle includes a bore configured to receive the stem such that the saddle is configured to self-align with the spinal rod as the set screw is rotated about the longitudinal axis with respect to the body.

18. An assembly configured to couple a spinal rod to a vertebra, the assembly comprising:
a body that is elongat

Assignees

• Depuy Synthes Products Inc

Inventors

• Keyer Thomas
• Capozzoli Joseph
• Mcdivitt Eric

Classifications

• A61B17/7037 Primary

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

• A61B17/7082

  for driving, i.e. rotating, screws or screw parts specially adapted for spinal fixation, e.g. for driving polyaxial or tulip-headed screws · CPC title

• A61B17/864

  hollow, e.g. with socket or cannulated · CPC title

• A61B17/8841

  Tools specially adapted to engage a prosthesis · CPC title

• A61B17/7076

  for driving, positioning or assembling spinal clamps or bone anchors specially adapted for spinal fixation · CPC title