Polyaxial bone screw with shank-retainer insert capture

• US 20080234761A1
• Filed: 05/23/2008
• Published: 09/25/2008
• Est. Priority Date: 06/18/2003
• Status: Active Grant

• Current Assignee: Roger P. Jackson
• Original Assignee: Roger P. Jackson
• Inventors: Jackson, Roger P.
• Granted Patent: US 8,257,396 B2
• Time in Patent Office: Days
• US Class Current: 606/309
• CPC Class Codes: A61B 17/7032 Screws or hooks with U-shaped head or back through which longitudinal rods pass
• CPC Class Codes: A61B 17/7037 wherein pivoting is blocked when the rod is clamped

Abstract

A polyaxial bone screw assembly includes a threaded shank body member having an upper portion with an internal drive and, alternatively, a laterally extending alignment rib or fin. The bone screw assembly also includes a lockable receiver coupling member, an open retainer ring member having a slit or gap and a compression insert member. An inset conical or cylindrical surface on the shank upper portion frictionally engages a similarly shaped inner surface of the retainer ring. The receiver includes a restrictive lower opening that allows for uploading the shank upper portion and compressed retainer ring into the receiver cavity, but prevents passage of the retainer ring out of the receiver once the ring inner surface engages the conical surface of the shank upper portion.

Claims

1. A polyaxial bone anchor comprising:

a) a shank having a body for fixation to a bone and an upper portion, the body and upper portion being generally aligned along an axis of rotation thereof, the upper portion having an upper surface, a first section and a second section, the first section being adjacent the upper surface, the first section having a first width measured perpendicular to the axis, the second section having a second width measured perpendicular to the axis, the second width being different than the first width, the second section being disposed between the body and the first section;

b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a seating surface partially defining a cavity, the channel communicating with the cavity, the cavity communicating with an external of the base through an opening sized and shaped to receive the shank upper portion therethrough;

c) a compression insert disposed in the receiver, the insert having a mating surface exclusively frictionally engageable with the upper surface of the shank upper portion; and

d) a retainer having a through slit and an internal surface sized and shaped to closely receive the shank upper portion at the second section, the shank upper portion and the retainer being in fixed relation to one another, both the upper portion and the retainer being in swivelable relation within the receiver, providing selective angular positioning of the shank with respect to the receiver, the retainer being in slidable engagement with the receiver seating surface, the retainer being substantially spaced from the compression insert at any and all angular positions of the shank with respect to the receiver.

2. The bone anchor of claim 1 wherein the first section is substantially cylindrical.

3. The bone anchor of claim 1 wherein the second section is substantially cylindrical.

4. The bone anchor of claim 1 wherein the second section is at least partially conical.

5. The bone anchor of claim 1 further comprising a rib projecting laterally from at least the shank second section, the rib being disposed within the through slit of the retainer.

6. The bone anchor of claim 5 wherein the rib projects laterally from a portion of the first section, the rib being spaced from the shank upper surface.

7. The bone anchor of claim 1 wherein the compression insert mating surface is concave and the shank upper surface is convex.

8. The bone anchor of claim 1 wherein the receiver seating surface is at least partially spherical and the retainer has an outer at least partially spherical surface.

9. The bone anchor of claim 1 wherein the shank upper portion has a tool engagement formation formed thereon adapted for non-slip engagement by a tool for driving the bone screw shank body into bone.

10. The bone anchor of claim 1 wherein the retainer is sized and shaped to be bottom-loadable into the receiver.

11. The bone anchor of claim 1 wherein the retainer comprises first and second spaced ends, the retainer being compressible and expandible with the first and second ends being movable toward and away from one another.

12. The bone anchor of claim 11 wherein the retainer has a central axis, the first and second ends each being substantially planar surfaces running substantially parallel to the axis.

13. The bone anchor of claim 11 wherein the retainer has a central axis, the first and second ends each being substantially planar surfaces running at an angle oblique to the axis.

14. The bone anchor of claim 1 wherein the bone screw shank is cannulated.

15. The bone anchor of claim 1 further comprising a closure structure insertable into the receiver, the closure structure for operably urging the insert into fixed frictional engagement with the bone screw shank upper portion and moving the shank in a direction to frictionally lock the position of the retainer with respect to the receiver, thereby locking the shank body in a selected angle with respect to the receiver.

16. The bone anchor of claim 15 wherein:

a) the receiver has upstanding spaced arms defining the open channel, the arms having guide and advancement structures on an inside surface thereof; and

b) the closure structure is sized and shaped to be positionable between the arms for closing the channel, the closure structure having a closure guide and advancement structure for rotatably mating with the guide and advancement structures on the arms, biasing the closure structure upon advancement rotation against a longitudinal connecting member disposed in the channel.

17. The bone anchor of claim 1 further comprising resilient structure extending from the receiver and biasing against the compression insert at a depression formed in a surface of the insert, the resilient structure prohibiting rotational movement of the compression insert within the receiver.

18. The assembly of claim 17 wherein the resilient structure is a pair of opposed spring tabs attached to the receiver and extending toward a central axis of the receiver.

19. A polyaxial bone screw assembly comprising:

(a) a shank having a body for fixation to a bone and an upper portion, the upper portion having an upper surface, a conical surface portion and a non-conical surface portion adjacent the conical surface portion;

(b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a seating surface partially defining a cavity, the channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the shank upper portion therethrough; and

(c) a retainer having a top surface substantially spaced from the upper surface of the upper portion, the retainer defining a through slit and having an internal surface with a first inner surface portion sized and shaped to substantially frictionally engage the shank conical surface portion and a second inner surface sized and shaped to substantially frictionally engage a portion of the shank non-conical surface portion, the shank upper portion and the retainer being in fixed relation to one another, both the upper portion and the retainer being in swivelable relation within the receiver, providing selective angular positioning of the shank with respect to the receiver, the retainer having an outer surface in slidable engagement with the receiver seating surface.

20. The assembly of claim 19 further comprising a compression insert disposed adjacent the shank upper portion and substantially spaced from the retainer.

21. The assembly of claim 19 wherein the non-conical surface portion is substantially cylindrical.

22. The assembly of claim 19 further comprising a rib projecting laterally from at least the shank conical surface portion, the rib being disposed within the through slit of the retainer.

23. The assembly of claim 22 wherein the rib projects laterally from a portion of the non-conical surface portion, the rib being spaced from the shank upper surface.

24. A polyaxial bone screw assembly comprising:

(a) a shank having a body for fixation to a bone and an upper portion, the upper portion having a first conical surface portion and a laterally extending alignment structure;

(b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a seating surface partially defining a cavity, the channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the shank upper portion therethrough; and

(c) a retainer defining a through slot and having an internal surface with a second conical surface portion sized and shaped to substantially frictionally engage the first conical surface portion, the retainer slot sized and shaped for receiving the alignment structure.

25. The assembly of claim 24 further comprising a compression insert disposed adjacent the shank upper portion and substantially spaced from the retainer.

26. In a polyaxial bone screw assembly for surgical implantation and including a shank having an upper end and a threaded body for inserting into a bone and a receiver having an outward opening channel adapted to receive a longitudinal connecting member within the channel, the receiver having a shank receiving opening, the improvement comprising:

(a) a rib projecting laterally from the shank near the upper end;

(b) an open retainer structure frictionally engaging the rib; and

(c) a compression insert disposed adjacent the shank upper portion and substantially spaced from the retainer.

27. In a polyaxial bone screw assembly for surgical implantation and including a shank having a central axis of rotation, an upper end and a threaded body for inserting into a bone and a receiver having an outward opening channel adapted to receive a longitudinal connecting member within the channel, the receiver having a shank receiving opening, the improvement wherein:

a) the shank upper end has an upper surface, a first outer surface generally disposed about the central axis and a second outer surface also disposed about the central axis and being inset from the first outer surface; and

further comprising;

b) a compression insert disposed in the receiver, the insert having a mating surface exclusively frictionally engageable with the shank upper surface; and

c) a retainer having a through slit and an internal surface sized and shaped to closely receive the shank at the insert surface, the shank upper end and the retainer being in fixed relation to one another, both the shank and the retainer being in swivelable relation within the receiver, providing selective angular positioning of the shank with respect to the receiver, the retainer being in slidable engagement with a receiver seating surface, the retainer being substantially spaced from the compression insert at any and all angular positions of the shank with respect to the receiver.