Polyaxial bone anchor with pop-on shank and friction fit retainer with low profile edge lock
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 securing an elongate rod to a bone, the bone anchor assembly comprising:
a bone anchor having a proximal portion with an at least partially spherical outer surface and an integral anchor portion extending distally from the proximal portion for attachment to the bone;
a receiver comprising a base with an internal cavity having a bottom opening in communication with a bottom surface of the base, and a pair of integral arms extending upwardly from the base to define a U-shaped upper channel with inner sidewall surfaces having structure to mate with a closure to close the upper channel; the upper channel communicating with the internal cavity to define a central bore, the internal cavity having a wider upper portion and a lower locking portion below the wider upper portion defined by a narrower width of the internal cavity adjacent the bottom opening, the central bore including an inwardly-facing interference wedging surface below the closure mating structure;
a pressure insert movably disposed within the upper channel and central bore and having an upper curved saddle seating surface sized and shaped for engaging the elongate rod, the pressure insert having an exterior surface for engaging the receiver at the inwardly-facing interference wedging surface when the curved saddle seating surface is aligned with the upper channel to restrict movement of the pressure insert upward through the central bore; and
a separate retainer movably disposed within the internal cavity and having a lower portion and an upper portion, the retainer upper portion having top surfaces engageable with an underside surface of the pressure insert and the retainer lower portion having at least one slit formed through a thickness thereof, the retainer lower portion being able to widen within the wider upper portion of the internal cavity to receive the bone anchor proximal portion as it is uploaded through the bottom opening and then to close around and capture the bone anchor proximal portion within the internal cavity while allowing for pivotal motion of the bone anchor relative to the receiver, the retainer and pressure insert being disposed within the receiver before the bone anchor, with the retainer being non-pivoting with respect to the receiver after capturing the bone anchor proximal portion,
wherein upward movement of the retainer during the uploading of the bone anchor proximal portion is restricted by the engagement between the retainer top surfaces and the insert underside surface, and
wherein after the bone anchor proximal portion is captured within the retainer lower portion, the pressure insert is downwardly deployable with a first tool within the receiver from a first position until the exterior surface of the pressure insert comes into a forced interference wedging contact with the receiver interference wedging surface at a second position so as to inhibit the pressure insert from moving back up within the receiver cavity.
2. The pivotal bone anchor assembly of claim 1 , wherein the pressure insert is upwardly retrievable from the forced interference wedging contact using a second tool so as to release the bone anchor from a fixed angular orientation relative to the receiver.
3. The pivotal bone anchor assembly of claim 1 , wherein the pressure insert has a generally elongate shape with rounded ends, as viewed from above, with a long axis extending perpendicular to an axis of the upper curved saddle seating surface.
4. The pivotal bone anchor assembly of claim 1 , wherein the retainer is downwardly deployable within the receiver until an outer surface of the retainer engages the receiver lower locking portion to lock the bone anchor in a fixed angular orientation.
5. The pivotal bone anchor assembly of claim 1 , wherein the retainer is resiliently expandable so as to capture the bone anchor proximal portion therein.
6. The pivotal bone anchor assembly of claim 1 , wherein the retainer frictionally engages the bone anchor proximal portion upon capture within the internal cavity to allow for an unlocked but non-floppy positioning of the bone anchor relative to the receiver prior to a final locking of the pivotal bone anchor assembly.
7. The pivotal bone anchor assembly of claim 1 , wherein the retainer is an integral open resilient ring.
8. The pivotal bone anchor assembly of claim 1 , wherein the closure has a receiver mating structure formed into an outer sidewall surface thereof engageable with the closure mating structure formed into the inner sidewall surfaces of the upwardly-extending arms to capture the elongate rod within the U-shaped upper channel.
9. The pivotal bone anchor assembly of claim 8 , wherein the closure receiver mating structure and the receiver closure mating structure each comprise complimentary helical threads formed into the outer sidewall surface of the closure and the inner sidewall surface of the receiver, respectively.
10. The pivotal bone anchor assembly of claim 1 , wherein the receiver is attachable to the bone anchor proximal portion after the integral anchor portion is fixed to the bone.
11. The pivotal bone anchor assembly of claim 1 , wherein the upwardly-extending receiver arms prevent rotation of the elongate rod around a longitudinal axis of the receiver once the elongate rod is positioned within the U-shaped upper channel.
12. The pivotal bone anchor assembly of claim 1 , wherein the receiver further includes spring tabs engageable with complimentary recesses formed into outer surfaces of the pressure insert to restrict rotation of the pressure insert around a longitudinal axis of the receiver once the curved saddle seating surface becomes aligned with the upper channel.
13. A pivotal bone anchor assembly for securing an elongate rod to a bone, the bone anchor assembly comprising:
a bone anchor having a proximal portion with an at least partially spherical outer surface and an integral anchor portion extending distally from the proximal portion for attachment to the bone;
a receiver comprising a base with an internal cavity having a bottom opening in communication with a bottom surface of the base, and a pair of integral arms extending upwardly from the base to define a U-shaped upper channel having inner sidewall surfaces with downward-facing seating surfaces formed therein, the upper channel communicating with the internal cavity to define a central bore, the internal cavity having a wider upper portion and a lower locking portion below the wider upper portion defined by a narrower width of the internal cavity adjacent the bottom opening, the central bore including an inwardly-facing interference wedging surface below the downward-facing seating surfaces;
a pressure insert movably disposed within the upper channel and central bore and having an upper curved saddle for engaging the elongate rod, the curved saddle having opposed top surfaces engageable with the receiver downward-facing seating surfaces when the curved saddle is aligned with the upper channel to restrict movement of the pressure insert upward through the upper channel; and
a retainer movably disposed within the internal cavity and having a lower portion and an upper portion, the retainer upper portion having top surfaces engageable with an underside surface of the insert and the retainer lower portion having at least one slit formed through a thickness thereof, the retainer lower portion being expandable within the wider upper portion of the internal cavity to receive the bone anchor proximal portion as it is uploaded through the bottom opening and then to close around and capture the bone anchor proximal portion within the internal cavity while allowing for pivotal motion of the bone anchor relative to the receiver, the retainer being non-pivoting with respect to the receiver after capturing the bone anchor proximal portion,
wherein upward movement of the retainer during the uploading of the bone anchor proximal portion is restricted by the pressure insert and the receiver downward-facing seating surfaces; and
wherein after the bone anchor proximal portion is captured within the retainer lower portion, the pressure insert is downwardly deployable with a first tool within the receiver until an outer surface of the pressure insert comes into a forced interference wedging contact with the receiver interference wedging surface to lock the bone anchor in a fixed angular orientation and to inhibit the pressure insert from moving back up within the receiver cavity.
14. The pivotal bone anchor assembly of claim 13 , wherein the pressure insert is upwardly retrievable from the forced interference wedging contact using a second tool to release the bone anchor from the fixed angular orientation relative to the receiver.
15. The pivotal bone anchor assembly of claim 13 , wherein the pressure insert has generally elongate shape with rounded ends, as viewed from above, with a long axis extending perpendicular to an axis of the upper curved saddle.
16. The pivotal bone anchor assembly of claim 13 , wherein the retainer is downwardly deployable with the receiver until an outer surface of the retainer engages the receiver lower locking portion to lock the bone anchor in the fixed angular orientation.
17. The pivotal bone anchor assembly of claim 13 , wherein the retainer frictionally engages the bone anchor proximal portion upon capture within the internal cavity to allow for an unlocked but non-floppy positioning of the bone anchor relative to the receiver prior to a final locking of the pivotal bone anchor assembly.
18. The pivotal bone anchor assembly of claim 13 , wherein the retainers are open resilient ring.
19. The pivotal bone anchor assembly of claim 13 , further comprising a closure having a receiver-mating structure formed into an outer sidewall surface thereof engageable with a complimentary closure-mating structure formed into the inner sidewall surfaces of the upwardly-extending arms to capture the elongate rod within the U-shaped upper channel.
20. The pivotal bone anchor assembly of claim 19 , wherein the closure receiver-mating structure and the receiver closure-mating structure each comprise complimentary helical threads formed into the outer sidewall surface of the closure and the inner sidewall surface of the receiver, respectively.
21. The pivotal bone anchor assembly of claim 20 , wherein the receiver downward-facing seating surfaces further comprises an upper surface of a run-out groove located below helical threads formed into the inner sidewall surface of the receiver.
22. The pivotal bone anchor assembly of claim 13 , wherein the receiver further includes spring tabs engageable with complimentary recesses formed into outer surfaces of the pressure insert to restrict rotation of the pressure insert around a longitudinal axis of the receiver once the curved saddle becomes aligned with the upper channel.