Pivotal bone anchor receiver assembly with rod and retainer engaging compression insert and bottom loaded shank
View Patent ↗A pivotal bone anchor assembly includes a receiver with a cavity and a rod-receiving channel having opposed interior surfaces with a downwardly-facing surface located below a discontinuous closure mating structure, and a shank having an upper capture portion uploadable into the receiver cavity through a bottom opening. The pivotal bone anchor assembly also includes a retainer disposed within the receiver cavity for capturing the shank upper capture portion therein, and a compression insert disposed within the receiver channel having an upper rod-engaging surface, a lower retainer-engaging surface, and an overlapping arrangement with the receiver channel downwardly-facing surface to inhibit upward movement of the compression insert within the receiver after the retainer has captured the shank upper capture in the receiver cavity, with the compression insert remaining spaced apart from the shank upper capture portion when the shank is pivoted with respect to the receiver.
1. A pivotal bone anchor assembly for a securing a longitudinal connecting member to a bone via a closure, the pivotal bone anchor assembly comprising:
a receiver including a lower body and a pair of upright arms extending upward from the lower body with opposed interior surfaces defining a receiver channel for receiving the longitudinal connecting member therebetween, the interior surfaces having a discontinuous mating structure for mating with the closure and a separate downwardly-facing surface formed therein, the downwardly facing surface being located below the discontinuous mating structure, the lower body defining a cavity in communication with the receiver channel and with a bottom surface of the receiver through a bottom opening and having an internal surface;
a shank having an upper capture portion integral with a lower anchor portion, the lower anchor portion being threaded for attachment to the bone, the upper capture portion including a lower spherical shaped segment and an upper internal recess for receiving a driving tool, the upper capture portion being configured for uploading into the receiver cavity through the bottom opening;
a retainer disposed within the receiver cavity prior to the shank and engageable with the shank upper capture portion to capture and hold the shank upper capture portion within the receiver cavity with the lower anchor portion extending downward through the receiver bottom opening so as to allow for pivotal movement between the shank and the receiver, the retainer being positioned between the shank upper capture portion and the receiver cavity internal surface and engageable with the receiver cavity internal surface; and
an insert having an upper longitudinal connecting member engaging surface disposed within the receiver channel and a lower surface engageable with an outer surface of the retainer, the insert further having an overlapping arrangement with the receiver downwardly facing surface to inhibit upward movement of the insert within the receiver after the retainer has captured the shank in the receiver cavity and prior to locking the shank and securing the longitudinal connecting member within the receiver via the closure,
wherein the insert remains spaced apart from the shank upper capture portion when the shank is pivoted with respect to the receiver.
2. The pivotal bone anchor assembly of claim 1 , wherein the receiver discontinuous mating structure further comprises a helically wound guide and advancement structure configured to resist splaying of the pair of upwardly extending arms upon mating with the closure.
3. The pivotal bone anchor assembly of claim 2 , wherein the helically wound guide and advancement structure is a square thread.
4. The pivotal bone anchor assembly of claim 2 , wherein the helically wound guide and advancement structure is a reverse angle thread.
5. The pivotal bone anchor assembly of claim 2 , wherein the helically wound guide and advancement structure is a buttress thread.
6. The pivotal bone anchor assembly of claim 1 , wherein the receiver channel blocks rotation between the receiver and the longitudinal connecting member when the longitudinal connecting member is positioned within the receiver channel.
7. The pivotal bone anchor assembly of claim 1 , wherein the closure further comprises two separate pieces.
8. The pivotal bone anchor assembly of claim 7 , wherein at least one of the two separate pieces includes a continuous thread.
9. The pivotal bone anchor assembly of claim 1 , wherein the insert has a non-snap-fit engagement with the longitudinal connecting member.
10. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated.
11. The pivotal bone anchor assembly of claim 1 , wherein the shank upper capture portion lower spherical shaped segment has an outer partial spherical surface.
12. The pivotal bone anchor assembly of claim 1 , wherein the retainer has a collet shape that is fixed with respect to the receiver and articulates with respect to the shank.
13. The pivotal bone anchor assembly of claim 1 , wherein the retainer is compressible.
14. The pivotal bone anchor assembly of claim 1 , wherein the retainer has a top surface, a bottom surface opposite the top surface and at least one missing section therebetween.
15. The pivotal bone anchor assembly of claim 1 , wherein the retainer is disposed within the receiver cavity through the receiver bottom opening.
16. The pivotal bone anchor assembly of claim 1 , wherein the shank is articulating with respect to the retainer and the retainer is not articulating with respect to the receiver after the shank upper capture potion is uploaded into the receiver cavity through the bottom opening and captured by the retainer.
17. The pivotal bone anchor assembly of claim 1 , wherein the insert has top surfaces that extend above a top surface on the longitudinal connecting member positioned against the insert upper engaging surface.
18. The pivotal bone anchor assembly of claim 1 , wherein the insert is top loaded into the receiver channel.
19. The pivotal bone anchor assembly of claim 1 , wherein the insert includes a central through-bore.
20. The pivotal bone anchor assembly of claim 1 , wherein the insert includes a lateral projection near a top surface on the insert.
21. The pivotal bone anchor assembly of claim 1 , wherein the insert lower surface has an overlapping compressive engagement with the retainer.
22. The pivotal bone anchor assembly of claim 1 , wherein the insert upper longitudinal connecting member engaging surface is curvate.
23. The pivotal bone anchor assembly of claim 1 , wherein the insert is positioned downwardly with a tool within the receiver after the shank is bottom loaded into the receiver cavity and captured by the retainer.
24. The pivotal bone anchor assembly of claim 1 , wherein the overlapping arrangement between the insert and the receiver downwardly facing surface further comprises the downwardly facing surface being formed into the receiver interior prior to the insert being positioned within the receiver.
25. The pivotal bone anchor assembly of claim 24 , wherein the insert is pushed at least partially passed the downwardly facing surface after the shank is captured in the receiver by the retainer.