Uniplanar bone anchor assembly with pop-on shank and insert with tool deployment
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable compression insert has a lower friction fit collet and an outer receiver press fit surface. A down-loadable retaining ring has at least one inner edge and outer tiered surfaces. The ring cooperates with the shank to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled. A uni-planar assembly is included.
1. A pivotal bone anchor assembly for securing an elongate rod to a bone via a closure top, the pivotal bone anchor assembly comprising:
a receiver having a top portion and a base, the top portion with upwardly extending arms defining an open channel for receiving the elongate rod and including a mating structure for mating with the closure top, the base defining a cavity in communication with the open channel and having a lower opening in communication with a bottom surface of the base, a locking region proximate the lower opening, and a capture region above the locking region, the receiver including an internal interference wedging surface between the capture region and the mating structure;
a shank having a body for fixation to the bone and an upper portion integral with the body and having an at least partial spherical shape providing pivotal motion of the shank with respect to the receiver;
an insert positioned within the receiver prior to the shank upper portion and engageable with the elongate rod when the elongate rod is received within the open channel, the insert being positioned adjacent to the receiver interference wedging surface with the receiver interference wedging surface resisting downward movement of the insert relative to the receiver upon said positioning; and
a retainer positionable within the receiver cavity prior to the shank upper portion, the retainer being configured to widen within the receiver cavity capture region as the shank upper portion is uploaded through the receiver lower opening, and then to close back around the shank upper portion to capture the shank within the receiver, the retainer being downwardly displaceable into the receiver cavity locking region after capturing the shank upper portion,
wherein after the shank upper portion is captured by the retainer, the insert is downwardly displaceable with a tool into a frictional engagement with the receiver interference wedging surface, with the receiver interference wedging surface resisting upward movement of the insert relative to the receiver upon said frictional engagement, and
wherein the shank upper portion includes at least one outwardly facing planar surface configured to limit the pivotal motion of the shank with respect to the receiver to a single plane.
2. The pivotal bone anchor assembly of claim 1 , further comprising at least one planar surface formed into an inner surface of the retainer and configured to slidably engage the at least one outwardly facing planar surface of the shank upper portion to limit the pivotal motion of the shank to the single plane.
3. The pivotal bone anchor assembly of claim 2 , wherein the at least one outwardly facing planar surface of the shank upper portion and the at least one planar surface of the retainer inner surface are parallel with a longitudinal centerline axis of the receiver.
4. The pivotal bone anchor assembly of claim 2 , wherein the retainer has a single piece construction.
5. The pivotal bone anchor assembly of claim 1 , wherein the retainer includes a slit or a slot.
6. The pivotal bone anchor assembly of claim 1 , wherein the retainer is top loaded into the receiver.
7. The pivotal bone anchor assembly of claim 1 , wherein the retainer is contained within the receiver cavity capture region so as to capture the shank upper portion while the shank upper portion is uploaded through the receiver lower opening.
8. The pivotal bone anchor assembly of claim 1 , wherein the retainer is non-pivoting with respect to the receiver after capturing the shank.
9. The pivotal bone anchor assembly of claim 1 , wherein the retainer comprises a ring-shaped structure having a radiused surface configured to guide the pivotal motion of the shank with respect to the receiver within the single plane.
10. The pivotal bone anchor assembly of claim 1 ,
wherein the insert is downwardly displaceable within the receiver into the frictional engagement by direct pushing engagement with a first tool, and
wherein the insert is releasable from the frictional engagement by direct pulling engagement with a second tool.
11. The pivotal bone anchor assembly of claim 10 , wherein the insert includes an internal recess engaged by the second tool.
12. The pivotal bone anchor assembly of claim 1 , wherein the insert is top loaded into the receiver.
13. The pivotal bone anchor assembly of claim 1 , wherein a bottom surface of the insert engages the shank upper portion.
14. The pivotal bone anchor assembly of claim 1 , wherein the receiver cavity capture region further includes a downwardly facing surface that engages a top surface of the retainer to hold the retainer in the capture region while the shank upper portion is uploaded through the receiver lower opening.
15. The pivotal bone anchor assembly of claim 1 , wherein the receiver includes a retainer alignment structure mateable with the retainer to hold the retainer in a desired rotational position with respect to the receiver.
16. The pivotal bone anchor assembly of claim 1 , wherein the receiver further includes a discontinuous downwardly facing annular surface between the interference wedging surface and the mating structure for preventing upward movement of the insert relative to the receiver upon the positioning of the insert within the receiver.
17. The pivotal bone anchor assembly of claim 1 , wherein the receiver includes an insert alignment structure mateable with the insert to hold the insert in a desired rotational position with respect to the receiver.
18. The pivotal bone anchor assembly of claim 1 , wherein the receiver mating structure further comprises a partial helically wound guide and advancement structure.
19. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated.
20. The pivotal bone anchor assembly of claim 1 , wherein the shank upper portion includes a planar top surface.
21. The pivotal bone anchor assembly of claim 1 , wherein the shank upper portion includes an internal tool mating drive socket.