Pivotal bone anchor assembly with post-positioning compression insert 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, a down-loadable friction fit split retaining ring having inner and outer tangs and an up-loadable shank upper portion cooperate 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.
1. A pivotal bone anchor assembly for anchoring to patient bone, the assembly configured for deployment using a deployment tool prior to coupling with an elongated implant via a closure, the pivotal bone anchor assembly comprising:
a shank comprising a head and a bone engagement portion extending downwardly from the head;
a receiver comprising a body defining an internal cavity centered around a longitudinal axis, and first and second upright arms extending upward from the body to define an open channel extending transverse to the longitudinal axis and configured to receive the elongated implant, the open channel communicating with the internal cavity to define an axial bore having an inwardly-facing wedging surface, the internal cavity being in communication with a bottom of the receiver through a bottom opening centered about the longitudinal axis, the receiver further including an exterior tool attachment structure for gripping by the deployment tool;
a retainer having a central bore disposed within the receiver internal cavity before the shank head, the retainer being constrained while vertically displaceable within the receiver between a load position and a deployed position, the retainer being held in the load position via an interference arrangement within an upper region of the receiver internal cavity, with the retainer central bore centered about the receiver longitudinal axis and coaxial with the receiver bottom opening, and with the retainer being configured to retain the shank head within the receiver internal cavity upon the uploading of the shank head through the bottom opening and into the retainer central bored; and
a compression insert positionable inside the receiver before the shank head, the compression insert having an upper surface engageable by the deployment tool and a bottom surface overlapping and abutting a top surface of the retainer when the retainer is in the load position,
wherein prior to the elongated implant being secured in the receiver channel via the closure, the insert is downwardly deployable into an interference interface with the axial bore internal wedging surface by the deployment tool which is in a gripping engagement with the receiver exterior tool attachment structure, and
wherein the retainer and shank head are downwardly displaceable together toward a lower region of the receiver internal cavity and into the deployed position in which the retainer is compressed between an inner surface of the receiver internal cavity and an outer surface of the shank head.
2. The pivotal bone anchor assembly of claim 1 , wherein when the retainer is in the load position and the shank head is uploaded in the retainer central bore, frictional engagement between the retainer and the shank head is sufficient to result in non-floppy placement of the shank with respect to the receiver yet allow angular adjustment of the shank with respect to the receiver prior to the retainer and shank head being downwardly displaced into the deployed position.
3. The pivotal bone anchor assembly of claim 1 , wherein the retainer central bore remains centered about the receiver longitudinal axis and coaxial with the receiver bottom opening throughout the downward displacement of the retainer from the load position to the deployed position.
4. The pivotal bone anchor assembly of claim 1 , wherein the retainer is non-pivotal with respect to the receiver while the shank pivots relative to the receiver and the retainer.
5. The pivotal bone anchor assembly of claim 1 , wherein the retainer further includes an upper end, a lower end opposite the upper end, an outer boundary extending between the upper and lower ends, and an at least partially radiused inner boundary extending between the upper and bottom ends, the retainer central bore being defined by the inner boundary and extending between the upper end and the lower end.
6. The pivotal bone anchor assembly of claim 5 , wherein the retainer further includes a slit through a wall of the retainer defined between the inner boundary and the outer boundary, the slit extending between the upper and the lower ends.
7. The pivotal bone anchor assembly of claim 1 , wherein the upper surface of the compression insert engageable by the deployment tool further comprises a saddle surface.
8. The pivotal bone anchor assembly of claim 1 , wherein the interference interface against the axial bore internal wedging surface prevents the compression insert from moving back up within the receiver and maintains the retainer in the deployed position after the deployment tool is removed from the receiver.
9. The pivotal bone anchor of assembly of claim 1 , wherein the elongated implant does not contact the retainer.
10. The pivotal bone anchor assembly of claim 1 , wherein the compression insert is top-loaded into the receiver.
11. The pivotal bone anchor assembly of claim 1 , wherein the retainer is top-loaded into the receiver.
12. The pivotal bone anchor assembly of claim 1 , wherein the interference arrangement includes a radially outward force of the retainer being transmitted to an inner surface of the receiver.
13. The pivotal bone anchor assembly of claim 12 , wherein the transmitting of the radially outward force comes from direct physical contact between the retainer and the receiver inner surface.
14. The pivotal bone anchor assembly of claim 13 , wherein the retainer further comprises panels that bias radially outward in transmitting the radially outward force via direct physical contact with the receiver inner surface.
15. The pivotal bone anchor assembly of claim 1 , wherein the retainer is of a one-piece construction.
16. The pivotal bone anchor assembly of claim 1 , further comprising the closure and wherein, when the elongated implant is coupled with the pivotal bone anchor assembly via the closure, the closure engages the elongated implant but does not contact the compression insert.
17. The pivotal bone anchor assembly of claim 1 , further comprising the closure and wherein the closure mechanically engages with the receiver in coupling the elongated implant to the receiver, the elongated implant having been received in the channel.
18. The pivotal bone anchor assembly of claim 17 , wherein the closure mechanically engaging with the receiver includes rotating the closure into engagement with the receiver.
19. The pivotal bone anchor assembly of claim 17 , wherein the closure employs at least one of a square-shaped thread, a reverse angle thread, or a buttress thread in mechanically engaging with the receiver.
20. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated.
21. A pivotal bone anchor assembly for anchoring to patient bone, the assembly configured for deployment using a deployment tool prior to coupling with an elongated implant, the pivotal bone anchor assembly comprising:
a shank comprising a head and a bone engagement portion extending downwardly from the head;
a receiver comprising a body defining an internal cavity centered around a longitudinal axis, and first and second upright arms extending upward from the body to define an open channel extending transverse to the longitudinal axis and configured to receive the elongated implant, the open channel communicating with the internal cavity to define an axial bore having an internal wedging surface, the internal cavity being in communication with a bottom of the receiver through a bottom opening centered about the longitudinal axis, the receiver further including an exterior tool attachment structure for gripping engagement by the deployment tool;
a retainer disposed within the receiver internal cavity before the shank head, the retainer having a central bore and being displaceable within the receiver internal cavity from a load position in an upper region of the internal cavity to a deployed position in a lower region of the internal cavity, the retainer being held in the load position with the central bore centered about the receiver longitudinal axis above the receiver bottom opening, and being configured to receive and retain the shank head upon an uploading of the shank head into the receiver internal cavity through the bottom opening and into the retainer central bore; and
a compression insert positionable inside the receiver before the shank head, the compression insert having an upper surface engageable by the deployment tool and a bottom surface overlapping and abutting a top surface of the retainer when the retainer is in the load position,
wherein the insert is configured for downward deployment by the deployment tool, prior to the elongated implant being secured in the receiver open channel via the closure, into an interference interface with the axial bore internal wedging surface, with the deployment tool also being in the gripping engagement with the receiver exterior tool attachment structure, and
wherein the retainer and shank head are downwardly displaceable together into the deployed position, with the retainer being compressed between an inner surface of the receiver internal cavity and an outer surface of the shank head.
22. The pivotal bone anchor assembly of claim 21 , wherein when the shank head is received with the retainer central bore with the retainer in the load position, frictional engagement between the retainer and the shank head is sufficient to result in non-floppy placement of the shank with respect to the receiver yet allow angular adjustment of the shank with respect to the receiver prior.
23. The pivotal bone anchor assembly of claim 21 , wherein the retainer is non-pivotal with respect to the receiver while the shank pivots relative to the receiver and the retainer.
24. The pivotal bone anchor assembly of claim 21 , wherein the retainer is of a one-piece construction.
25. The pivotal bone anchor assembly of claim 21 , wherein the retainer further includes an upper end, a lower end opposite the upper end, an outer boundary extending between the upper and lower ends, and an at least partially radiused inner boundary extending between the upper and lower ends and defining the retainer central bore.
26. The pivotal bone anchor assembly of claim 25 , wherein the retainer further includes at least one slit through a wall of the retainer and extending between the upper and the lower ends.
27. The pivotal bone anchor assembly of claim 21 , wherein the retainer is maintained in the load position by a compression arrangement between elements of the pivotal bone anchor assembly including the retainer and the receiver.
28. The pivotal bone anchor assembly of claim 21 , wherein the retainer is maintained in the load position by a radially outward force of the retainer being transmitted to an inner surface of the receiver.
29. The pivotal bone anchor assembly of claim 28 , wherein the transmitting of the radially outward force comes from direct physical contact between the retainer and the receiver inner surface.
30. The pivotal bone anchor assembly of claim 29 , wherein the retainer further comprises panels that bias radially outward in transmitting the radially outward force via direct physical contact with the receiver inner surface.
31. The pivotal bone anchor assembly of claim 21 , wherein the upper surface of the compression insert further comprises a saddle surface.
32. The pivotal bone anchor assembly of claim 21 , wherein the interference interface against the axial bore internal wedging surface prevents the compression insert from moving back up within the receiver and maintains the retainer in the deployed position after the deployment tool is removed from the receiver.
33. The pivotal bone anchor assembly of claim 21 , wherein the compression insert includes an axial bore that remains centered about the receiver longitudinal axis.
34. A pivotal bone anchor assembly for anchoring to patient bone for deployment using a deployment tool, and for coupling with an elongated implant via a closure, the pivotal bone anchor assembly comprising:
a shank comprising a head and a bone engagement portion extending downwardly from the head; and
a receiver subassembly having a longitudinal axis and configured to couple with the shank head, the receiver subassembly including:
a receiver comprising a body defining an internal cavity centered around a longitudinal axis, and first and second upright arms extending upward from the body to define an open channel extending transverse to the longitudinal axis and configured to receive the elongated implant, the internal cavity being in communication with the channel and with a bottom of the receiver through a bottom opening centered about the longitudinal axis, the receiver further including an exterior tool attachment structure for gripping by the deployment tool;
a retainer being disposed into a load position within the receiver internal cavity before the shank head, the retainer having a central bore centered about the receiver subassembly longitudinal axis and coaxial with the receiver bottom opening and being configured to capture the shank head upon an uploading of the shank head into the receiver internal cavity through the bottom opening and into the retainer central bore; and
a compression insert having an upper surface engageable with the elongated implant and a bottom surface engageable with a top surface on the retainer while the retainer is maintained in an upper portion of the receiver internal cavity, the compression insert being disposed within the receiver channel before the shank head is uploaded through the receiver bottom opening and captured within the retainer,
wherein the retainer is held in the load position with a top outer surface of the compression insert abutting an overlying surface of the receiver to inhibit an upward movement of the compression insert and the retainer during the uploading of the shank head into the retainer central bore, and
wherein after the shank head is disposed within the retainer central bore, the compression insert is downwardly displaceable within the receiver by pressure from the deployment tool that is also in a gripping engagement with the receiver exterior tool attachment structure, until an external surface on the compression insert enters into an interference interface against an internal wedging surface of the receiver that prevents the compression insert from moving back up within the receiver and maintains the retainer in a deployed position after the deployment tool is removed from the receiver.