Polyaxial bone fixation element

Patent metadata

Field	Value
Publication number	US-11547449-B2
Application number	US-202016871085-A
Country	US
Kind code	B2
Filing date	May 11, 2020
Priority date	Feb 26, 2016
Publication date	Jan 10, 2023
Grant date	Jan 10, 2023

Abstract

A fastener device includes an anchor body that defines a through hole. The anchor body further includes an inner surface that defines a least a portion of the through hole. The fastener includes a head, a threaded shaft that extends out with respect to the head in a distal direction, and a neck between the head and threaded shaft. The head includes an outer surface configured to articulate along the inner surface when the fastener head is inserted in the through hole. At least a portion of the outer surface is convex and defines a portion of a sphere that defines a first diameter. The neck defines a second diameter and the fastener defines a ratio of the first diameter to the second diameter in a range between about 2 to 1 and about 3 to 1.

First claim

We claim:

1. A fastener device configured to secure a spinal rod relative to a bone, the fastener device comprising:
an anchor body including an anchor body housing, the anchor body defining a through hole that extends through the anchor body housing, the anchor body further defining a rod-receiving channel that is configured to receive the spinal rod, the anchor body further including an upper end, a lower end, and an inner surface, the inner surface defining at least a portion of the through hole; and
a fastener including a head, a threaded shaft that extends out with respect to the head in a distal direction, and a neck that extends between the head and the threaded shaft, the head including a convex outer surface, a portion of the convex outer surface both defining a portion of a sphere and being configured to articulate relative to the inner surface when the head is positioned in the through hole, the fastener including a concave surface that extends along both a distal most portion of the head and the neck,
wherein the fastener is configured such that all lines that: 1) lie entirely within a plane parallel to the distal direction, and 2) are tangent to the portion of the convex outer surface are noncollinear with all lines that: 1) lie entirely within the plane, and 2) are tangent to the concave surface.

2. The fastener device of claim 1 , wherein the through hole extends away from the upper end and toward the lower end in a longitudinal direction, and the inner surface defines a minimum inner diameter at an anchor location on the inner surface, such that the anchor location is closer to the lower end as measured along the longitudinal direction, than the anchor location is to the upper end as measured along the longitudinal direction.

3. The fastener device of claim 1 , wherein the lower end defines a lower opening where the through hole exits the anchor body housing, the anchor body defines a plane that includes an entirety of the lower opening, the head of the fastener defines a fastener location such that the fastener is devoid of any locations positioned in a proximal direction, which is opposite the distal direction, from the fastener location, and the fastener device defines a configuration in which the fastener location is positioned a first distance from the upper end, the lower end is positioned a second distance from the upper end, the first distance and the second distance are each measured along the longitudinal direction, and the first distance is greater than the second distance.

4. The fastener device of claim 1 , wherein the sphere defines a first diameter, the through hole extends along a central anchor body axis, the inner surface defines a minimum inner diameter that is both: 1) measured at a location that is on the inner surface, and 2) measured in a direction perpendicular to the central anchor body axis, and the first diameter is larger than the minimum inner diameter.

5. The fastener device of claim 1 , further comprising a stabilization mechanism configured to be positioned in the through hole such that when the fastener is inserted in the through hole such that the outer surface contacts the inner surface the stabilization mechanism exerts a force on the fastener that resists relative movement of the fastener and the anchor body.

6. The fastener device of claim 5 , wherein the stabilization mechanism includes a biasing member configured to expand as the head of the fastener contacts the biasing member, such that the expanded biasing member exerts the force on the outer surface of the fastener.

7. The fastener device of claim 6 , wherein the anchor body defines a recess configured to receive the biasing member such that the biasing member is captured within the recess.

8. The fastener device of claim 1 , wherein the portion of the sphere terminates at an intermediate surface that terminates at the concave surface, and wherein the intermediate surface is flat or has a curvature different from the portion of the sphere and the concave surface.

9. The fastener device of claim 1 , wherein the portion of the convex outer surface defines every location on the head that is configured to contact the inner surface when the head is positioned in the through hole, wherein the portion of the sphere terminates at an intermediate surface that terminates at the concave surface, and wherein the intermediate surface is flat or has a curvature different from the portion of the sphere and the concave surface.

10. A fastener device configured to secure a spinal rod relative to a bone, the fastener device comprising:
an anchor body including an anchor body housing and a central axis, the anchor body defining a through hole that extends through the anchor body housing along the central axis, the anchor body further defining a rod-receiving channel that is configured to receive the spinal rod, the anchor body further including an upper end, a lower end spaced from the upper end in a first direction, and an inner surface that defines at least a portion of the through hole, the inner surface including: 1) a first portion that defines a portion of a sphere having a first diameter, 2) a second portion that is cylindrical and that defines a second diameter that is equal to or greater than the first diameter, and 3) a third portion that defines a recess that defines a third diameter that is greater than both the first diameter and the second diameter, wherein the portion of the sphere terminates at a first end of the recess in a direction that is opposite the first direction, and the third portion is disposed between the first portion and the second portion with respect to the first direction; and
a fastener including a head and a threaded shaft that extends out with respect to the head, the head including an outer surface configured to articulate relative to the first portion of the inner surface when the head is inserted in the through hole.

11. The fastener device of claim 10 , further comprising a biasing member configured to be inserted into the through hole and positioned such that the biasing member is aligned with the third portion along a second direction that is perpendicular to the first direction.

12. The fastener device of claim 11 , wherein the biasing member is a split ring that includes an inner surface that faces the central axis when the split ring is inserted in the through hole, the split ring defines a fourth diameter measured from a first point on the inner surface, through the central axis, to a second point on the inner surface in the second direction, and when the split ring is in an unbiased state the fourth diameter is less than each of the first diameter, the second diameter, and the third diameter.

13. The fastener device of claim 10 , wherein the sphere is a first sphere, the threaded shaft extends out with respect to the head in a distal direction, the fastener includes a neck that extends between the head and the threaded shaft, at least a portion of the outer surface is convex and defines a portion of a second sphere, the second sphere defining a first fastener diameter, the fastener includes a concave surface that extends along both the head and the neck, the neck defines a second fastener diameter measured: 1) in a direction perpendicular to the distal direction, and 2) at a location spaced in the distal direction of an entirety of the concave surface, and the fastener defines a ratio of the first fastener diameter to the second fastener diameter in a range between about 2 to 1 and about 3 to 1.

14. The fastener device of claim 13 , wherein:
the fastener is elongate along a central axis that is parallel to the distal d

Assignees

• Medos Int Sarl

Inventors

• Ramsay Christopher
• Di Vincenzo John

Classifications

• A61B17/7037 Primary

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

• A61B17/7001 Primary

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

• A61B17/8605

  Heads, i.e. proximal ends projecting from bone · CPC title

• A61B17/8685

  comprising multiple separate parts · CPC title

• A61B17/7038

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