Bone anchor receiver with horizontal radiused tool attachment grooves and 2-part closure
A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver member or head, a retaining and articulating structure, and a pressure insert disposed between the shank upper portion and a rod. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod and a receiver cavity. The retaining and articulating structure attaches to the shank and rotates with the shank in the cavity during positioning. The pressure insert presses upon the shank upper portion and not the retaining and articulating structure.
1. A bone anchor assembly configured for attachment to a rod, the bone anchor assembly comprising:
a shank having an integral upper end portion with an outer spherical surface on the integral upper end portion;
a receiver having a set of upright arms each having an inner surface, an upper outer surface opposite the inner surface, a front side surface, a back side surface opposite the front side surface, and a top surface, the receiver in pivotal relation with the integral upper end portion of the shank,
at least one horizontally-elongated radiused upper tool engaging groove formed into the upper outer surface of each upright arm, with each upper tool engaging groove being spaced a fixed distance below the top surfaces and extending to at least one of the front side surface and the back side surface;
a channel defined by the set of arms for positioning the rod therebetween;
an outer fastener having a closed body with a top surface, a bottom surface, and an outer surface;
a closure helically wound thread extending continuously along at least a portion of the outer surface and engageable in a splay resisting relationship with a receiver helically wound thread extending discontinuously along the inner surfaces of the set of upright arms;
a central bore extending between the top surface and the bottom surface, the central bore having at least a portion with an internal surface guide and advancement thread form;
an inner set screw having a continuous outer surface thread and a lower portion closed off by a continuously solid bottom surface, the continuous outer surface thread engageable to the internal surface guide and advancement structure when the set screw is threadably inserted into the outer fastener, wherein when the outer fastener and the inner set screw are disposed within the channel defined by the set of arms in a locked position, the top surfaces and the upper outer surfaces of the set of upright arms are completely uncovered by the fastener and the set screw in the locked position; and
an opening having an internal drive structure formed into the inner set screw, the internal drive structure extending within the lower portion and ending at a terminal abutment surface, the opening not intersecting the continuously solid bottom surface.
2. The bone anchor assembly of claim 1 , wherein the shank integral upper end portion includes a top radiused surface with a central opening.
3. The bone anchor assembly of claim 2 , wherein the central opening extends into the shank integral upper end portion.
4. The bone anchor assembly of claim 1 , wherein the shank is cannulated.
5. The bone anchor assembly of claim 1 , wherein the continuously solid bottom surface of the inner set screw is flat.
6. The bone anchor assembly of claim 1 , wherein the closed body bottom surface is tightened against the rod in the locked position.
7. The bone anchor assembly of claim 1 , wherein no portion of the outer fastener or the inner set screw extends above the top surface of the set of arms in the locked position.
8. The bone anchor assembly of claim 1 , wherein the inner set screw remains spaced apart from the receiver in the locked position.
9. The bone anchor assembly of claim 1 , wherein the closure helically wound thread includes square threads.
10. The bone anchor assembly of claim 1 , wherein the receiver upright arms are configured to resist splay when the assembly is locked with the rod attached by the outer fastener and the inner set screw having a solid bottom surface compressed against the rod.
11. The bone anchor assembly of claim 1 , wherein the inner set screw has a central aperture that communicates with only a top thereof.
12. The bone anchor assembly of claim 1 , wherein the terminal abutment surface is located substantially nearer the bottom surface than a top surface of the inner set screw.
13. The bone anchor assembly of claim 1 , wherein each of the at least one horizontally-elongated upper tool engaging groove is positioned above a top surface of the rod positioned between the upright arms in a locked orientation.
14. The bone anchor assembly of claim 1 , wherein the closed body includes a driving structure configured for engagement with a tool.
15. The bone anchor assembly of claim 14 , wherein the driving structure on the closed body comprises a break-off head.
16. The bone anchor assembly of claim 1 , further comprising an insert positioned in the receiver after the shank and in direct engagement with the outer spherical surface on the integral upper end portion of the shank.
17. The bone anchor assembly of claim 16 , wherein the insert includes upright arms forming a rod-receiving channel therebetween.
18. The bone anchor assembly of claim 17 , wherein the insert upright arms include lateral protrusions.
19. The bone anchor assembly of claim 17 , wherein the receiver channel and the insert rod-receiving channel are aligned.
20. The bone anchor assembly of claim 16 , further comprising a ring positionable within a recess formed in the receiver below the channel, the insert being spaced above and apart from the ring, wherein when the insert and the ring are in contact with the integral upper end portion of the shank a friction fit is provided for the shank with respect to the receiver.
21. The bone anchor assembly of claim 20 , wherein the ring includes a slot.
22. The bone anchor assembly of claim 20 , wherein the insert is displaced downwardly within the receiver into contact with the shank.
23. The bone anchor assembly of claim 17 , wherein the insert has an overlapped engagement with a surface formed in the receiver.
24. The bone anchor assembly of claim 20 , wherein the ring is inserted into the receiver before the shank.
25. The bone anchor assembly of claim 16 , wherein the ring restrains the integral upper end portion of the shank from moving along a longitudinal axis of the receiver.