Polyaxial bone screw with shank articulation pressure insert and method

1. A pivoting bone anchor assembly comprising:

a) a shank having an upper capture portion with a lower annular projecting outer structure and a body for attachment to a bone;

b) a receiver defining an open channel and having a cavity with a lower interior surface opening onto a bottom surface of the receiver, the shank being pivotal with respect to the receiver during positioning of the shank after the shank is bottom loaded therein;

c) an open expandable retaining and articulating structure separate from the shank, is loaded into the cavity before the shank and positionable so as to be snapped on the shank upper capture portion, the shank upper capture portion limiting penetration of the upper capture portion into the open expandable retaining and articulating structure, wherein the open expandable retaining and articulating structure pivots together with said shank relative to the receiver during positioning of said shank; the shank upper capture portion extending above the open expandable retaining and articulating structure, the open expandable retaining and articulating structure having an outer surface for mating with and pivoting relative to the receiver interior surface during positioning of the shank relative to the receiver; and

d) an insert being loaded and operably positioned in the receiver above the shank, the shank upper capture portion having a top surface frictionally engaging the insert when the assembly is fully assembled so as to directly receive downward force from the insert so as to lock an angular position of the shank relative to the receiver.

2. The bone anchor assembly according to claim 1 , wherein the shank top surface is spherically shaped defining a first radius, and the open expandable retaining and articulating structure outer surface defining a second radius, wherein the first radius is less than the second radius.

3. The bone anchor assembly according to claim 1 , the shank upper capture portion including:

a) a tapered surface to engage a tapered surface within the open expandable retaining and articulating structure.

4. The assembly of claim 1 , wherein:

a) the insert includes a length and a width, the length being greater than the width.

5. The assembly of claim 1 , wherein:

a) the insert includes a rod receiving recess and is top-loaded into the receiver in a first orientation and then rotated to a second orientation, wherein, when in the second orientation, the insert rod receiving recess is aligned with the receiver open channel.

6. The assembly of claim 1 , wherein the annular projecting structure can pivot into the receiver cavity.

7. A bone anchor assembly comprising:

a) a shank having an upper portion with a capture connection having an annular projecting structure and a body for fixation to a bone;

b) a receiver defining an open channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank;

c) a retaining and articulating structure separate from the shank that is loaded into the cavity before the shank and configured to snap on the shank capture connection and to cooperate with the shank upper portion so as to pivot together with said shank relative to the receiver during positioning of said shank; the shank upper portion extending above the retaining and articulating structure, the retaining and articulating structure having a lower mating surface for mating with and pivoting relative to the receiver cavity lower interior surface during positioning of the shank relative to the receiver, the shank capture connection including structure to prevent the shank upper portion from being pushed up out of the retaining and articulating structure; and

d) an insert being operably positioned in the receiver above the shank, the shank upper portion frictionally engaging the insert when the assembly is fully assembled so as to directly receive downward force from the insert so as to lock an angular position of the shank relative to the receiver.

8. The assembly of claim 7 , wherein the capture connection has a surface that is tapered.

9. A bone anchor assembly comprising:

a) a shank having a body for fixation to a bone and an upper portion including a conical capture connection and an annular projecting structure;

b) a receiver defining an open channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank;

c) a retaining and articulating structure separate from the shank that is loaded into the cavity before the shank and configured to snap on the conical capture connection and to cooperate with the shank upper portion so as to pivot together with said shank relative to the receiver during positioning of said shank; the shank upper portion extending up to at least a top portion of the retaining and articulating structure, the retaining and articulating structure having a lower mating surface for mating with the annular projecting structure, the annular projecting structure limiting penetration of the capture portion into the retaining and articulating structure; and

d) an insert being operably positioned in the receiver above the shank, so as to exert a downward force so as to lock an angular position of the shank relative to the receiver.

10. A bone anchor assembly comprising:

a) a shank having a portion for attachment to a bone and an upper capture portion, the shank including a central axis aligned with a central bore along an entire length of the shank and opening onto a top surface of the shank;

b) a receiver defining an open channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank;

c) a retaining and articulating structure separate from the shank, is loaded into the cavity prior to the shank and connected to the shank upper capture portion, such that the shank top surface extending up to at least a top surface of the retaining and articulating structure, wherein the retaining and articulating structure pivots together with said shank relative to the receiver during positioning of said shank; the retaining and articulating structure having an outer surface for mating with and pivoting relative to the receiver interior surface during positioning of the shank relative to the receiver; and

d) an insert being operably positioned in the receiver above the shank and below a rod positioned in the receiver open channel, and wherein the rod remains spaced from the shank top surface.

11. The assembly of claim 10 , wherein the shank top surface is radiused.

12. A bone anchor assembly including a closure top and a rod, comprising:

a) a shank having an upper portion including a capture structure and a body for fixation to a bone;

b) a receiver having an open channel and having an interior surface which includes a lower cavity, the shank being pivotal with respect to the receiver during positioning of the shank in a non-locked configuration;

c) a retaining structure separate from the shank and positionable within the receiver to keep the shank upper portion within the receiver cavity during positioning of said shank in the non-locked configuration;

d) an insert being operably positioned in the receiver between the rod and the shank, so as to apply a downward force and to thereby lock an angular position of the shank relative to the receiver in a locked configuration; and wherein

e) when the insert is urged downwardly, frictional engagement of at least one exterior surface on the insert with the receiver interior surface produces a frictional engagement between the shank and the insert to resist any pivotal movement when the closure top and rod are disengaged from the receiver.

13. The assembly according to claim 12 , wherein the shank capture structure is tapered.

14. The assembly according to claim 12 , wherein the insert engagement with the receiver is an interference fit.

15. A bone anchor assembly comprising:

a) a shank having an upper portion and a body for fixation to a bone;

b) a receiver defining an open rod-receiving channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank;

c) a retaining structure separate from the shank and positioned within the cavity of the receiver, the retainer cooperating with the shank to retain the shank upper portion from exiting a lower opening in the receiver and to allow the shank to pivot relative to the receiver during positioning of the shank, the shank upper portion extending above the retaining structure; the retaining structure having a lower mating surface for engaging a lower interior receiver surface during positioning of the shank relative to the receiver; and

d) an insert being operably positioned in the receiver and above the shank, the shank having an upper end frictionally engaging the insert when the assembly is fully assembled so as to lock an angular position of the shank relative to the receiver; and the insert frictionally engaging the receiver and providing a friction fit for the shank with respect to the insert, so as to stabilize the bone anchor assembly when a rod is not in the receiver channel and when the rod is not firmly engaging the insert.

16. The assembly of claim 15 , wherein:

a) the insert includes a bottom surface that frictionally engages the shank upper portion, so as to from the friction fit.

17. The assembly of claim 16 , wherein:

a) the insert bottom surface engages a radiused surface on the shank upper portion.

18. The assembly of claim 15 , wherein:

a) the friction fit between the insert and the shank sets an angle of orientation of the receiver with respect to the shank.

19. The assembly of claim 15 , wherein:

a) the insert includes a length and a width, the length being greater than the width.

20. The assembly of claim 15 , wherein:

a) the insert is top-loaded into the receiver in a first orientation and then rotated to a second orientation, wherein, when in the second orientation, the insert is fixed in the receiver.

21. A bone anchor assembly comprising:

a) a shank having an upper portion and a body for fixation to a bone;

b) a receiver defining an open rod-receiving channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank with respect to the receiver;

c) a retaining structure separate from the shank and positioned within the cavity of the receiver, the retainer allowing the shank to pivot relative to the receiver during positioning of the shank; the retaining structure having a lower mating surface for engaging the receiver surface during positioning of the shank relative to the receiver; and

d) an insert operably positioned in the receiver and above the shank, the shank having an upper end extending above the retaining structure and frictionally engaging the insert when the assembly is fully assembled so as to lock an angular position of the shank relative to the receiver; and

e) the insert providing independent lock and release structures so that the bone anchor assembly can be locked when a rod is not in the receiver.

22. A bone anchor assembly comprising:

a) a shank having an upper portion and a body for fixation to a bone;

b) a receiver defining an open rod-receiving channel and having a cavity with a lower interior surface, the shank being pivotal with respect to the receiver during positioning of the shank extending from a bottom opening in the receiver;

c) a retaining structure separate from the shank and positioned within the cavity of the receiver, so as to keep the shank upper portion within the receiver, the retaining structure allowing the shank to pivot relative to the receiver during positioning of the shank; the retaining structure having a lower mating surface for engaging the receiver surface during positioning of the shank relative to the receiver;

d) an insert being operably positioned in the receiver and above the shank, the shank having an upper end positioned above the retaining structure and frictionally engaging the insert when the assembly is fully assembled so as to lock an angular position of the shank relative to the receiver; and

e) the insert having a friction fit with the receiver and the shank to stabilize the bone anchor assembly when a rod is not in the receiver.

23. A bone anchor assembly including a closure top and a rod, comprising:

a) a shank having an upper portion including a capture structure and a body for fixation to a bone;

b) a receiver having an open channel and having an interior surface which includes a lower cavity, the shank being pivotal with respect to the receiver during positioning of the shank in a non-locked configuration;

c) a retaining structure separate from the shank and positionable within the receiver to keep the shank upper portion within the receiver cavity during positioning of said shank in the non-locked configuration;

d) an insert being operably positioned in the receiver between the rod and the shank, so as to apply a downward force and to thereby lock an angular position of the shank relative to the receiver in a locked configuration; and wherein

e) when the insert is urged downwardly, frictional engagement of at least one exterior surface on the insert with the receiver interior surface produces a frictional engagement between the shank and the insert to resist any pivotal movement when the closure top and rod are disengaged from the receiver and wherein the insert engagement with the receiver interior surface is an interference fit.

24. A pivoting bone anchor assembly comprising:

a) a shank having a longitudinal axis extending through an upper capture portion, a body for attachment to a bone, and an opening centered around the axis along an entire length thereof;

b) a receiver defining a first channel and having a cavity with a lower interior surface opening onto a bottom surface of the receiver, the shank being pivotal with respect to the receiver during positioning after being positioned therein;

c) an insert being loaded and operably positioned in the receiver above the shank, the insert having upright arms forming a second channel, the upright arms extending below a top surface of a rod positioned within the second channel, the insert engaging a top surface of the shank upper capture portion, so as to lock an angular position of the shank relative to the receiver; and

d) an open expandable retaining structure separate from the shank is loaded into the cavity and positionable so as to be snapped around the shank upper capture portion and maintain the shank within the receiver, wherein the retaining structure allows pivoting of the shank relative to the receiver during positioning of said shank; the shank upper capture portion extending above the retaining structure, the retaining having an outer surface for engagement with the receiver interior surface during positioning of the shank relative to the receiver.