Bone anchor insert with rotation blocking extensions and tool forced displacement
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. The receiver can have crimp tabs, but is devoid of spring tabs and collet-like flexible structures. A down-loadable compression insert (some with lock and release feature), a down-loadable friction fit split retaining ring 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. The receiver and insert include aligned tool receiving apertures for lock and release of the polyaxial mechanism.
1. A pivotal bone anchor assembly for securing an elongate rod to a bone of a patient via a closure top and using tooling, the pivotal bone anchor assembly comprising:
a receiver having a receiver longitudinal axis, a lower body defining a cavity communicating with a bottom of the receiver through a bottom opening, and a pair of upstanding arms extending upwardly from the lower body to define an open channel configured to receive the elongate rod and having opposed interior surfaces with a closure-mating structure formed therein, the open channel communicating with the cavity to define a central bore, the receiver having recessed surfaces integrally formed into the opposed interior surfaces of the upstanding arms below the closure-mating structure;
a shank having a shank longitudinal axis, an upper end portion and an anchor portion extending distally from the upper end portion configured for attachment to the bone, the upper end portion configured to be uploaded into the cavity through the bottom opening; and
a compression insert configured to be positioned within the central bore in a first position before the shank is uploaded into the cavity, the compression insert having an insert longitudinal axis, an upwardly-facing curvate surface configured to engage the elongate rod, a lower portion configured to engage the upper end portion of the shank, laterally facing exterior surfaces configured for positioning within the recessed surfaces of the receiver, and opposed rotation-blocking extensions in the direction of the open channel having upper surfaces configured to be positioned underneath a most bottom surface of the elongate rod and when the elongate rod is received within the open channel, the compression insert in the first position being inhibited from moving upwardly and downwardly within the central bore by at least partial engagement between the laterally facing exterior surfaces and the recessed surfaces, and
wherein the compression insert is configured to be forcibly downwardly displaced into a second position within the central bore by direct engagement from a tool after the upper end portion is up-loaded into the cavity, with the laterally facing exterior surfaces of the compression insert coming into a forced interference engagement with inwardly-facing interference surfaces integrally formed into the opposed interior surfaces of the upstanding arms below the recessed surfaces, and thereafter being inhibited from moving back up within the central bore.
2. The pivotal bone anchor assembly of claim 1 , wherein the compression insert is configured to be forcibly downwardly displaced by a first tool that is configured to be removably inserted into the open channel along the receiver longitudinal axis.
3. The pivotal bone anchor assembly of claim 2 , wherein the compression insert is configured to be upwardly retrievable from the forced interference engagement using a second tool so as to release the upper end portion from a friction fit angular orientation relative to the receiver.
4. The pivotal bone anchor assembly of claim 1 ,
wherein the opposed rotation-blocking extensions include opposite outer most ends, and
wherein the upwardly-facing curvate surface extends substantially perpendicularly with respect to the insert longitudinal axis to the outer most ends of the extensions.
5. The pivotal bone anchor assembly of claim 1 , wherein the pair of upstanding arms of the receiver include breakoff extensions.
6. The pivotal bone anchor assembly of claim 1 , wherein the upper end portion of the shank has a shape that is at least partially spherical.
7. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated along an entire length thereof.
8. The pivotal bone anchor assembly of claim 1 , further comprising the closure top, and wherein the closure top includes a helically wound guide and advancement structure formed into an outer sidewall surface and configured to engage with the closure-mating structure formed into the opposed interior surfaces so as to capture the elongate rod within the open channel.
9. The pivotal bone anchor assembly of claim 8 , wherein the closure top includes a bottom opposite a top of the closure top, the bottom comprising an outer rim structure with a recessed bottom surface interior to the outer rim structure, the recessed bottom surface including a planar portion.
10. The pivotal bone anchor assembly of claim 9 , wherein the recessed bottom surface is configured to be spaced apart from the elongate rod when the closure top is engaged against the elongate rod.
11. The pivotal bone anchor assembly of claim 8 , wherein the closure top includes an internal tool engagement drive socket.
12. The pivotal bone anchor assembly of claim 1 ,
wherein the insert has central opening about the insert longitudinal axis, and
wherein the upwardly-facing curvate surface of the insert further comprises an upwardly open contact surface extending continuously between the central opening toward a most front end surface and a most back end surface of the rotation-blocking extensions and without upwardly projecting ridges or protrusions, the contact surface being configured to provide a substantially straight and continuous engagement with the most bottom surface of the rod across the length thereof.
13. The pivotal bone anchor assembly of claim 12 , wherein the upwardly open contact surface has a upwardly open partially cylindrical shape configured to provide a substantially straight and continuous engagement with a lower portion of a cylindrically-shaped rod.
14. A pivotal bone anchor assembly for securing an elongate rod to a bone of a patient using tooling, the pivotal bone anchor assembly comprising:
a receiver having a longitudinal axis, a lower body defining a cavity with a bottom opening, a channel having opposed interior surfaces configured to receive the elongate rod, and a helically wound structure formed in the receiver, the channel communicating with the cavity to define a central bore and including recessed surfaces integrally formed into the interior surfaces below the helically wound structure;
a shank having an upper end portion and an anchor portion extending distally from the upper end portion configured for attachment to the bone, the upper end portion configured to be uploaded into the cavity through the bottom opening; and
a compression insert configured to be downloaded into the central bore and having an upper surface configured to engage the elongate rod, exterior surfaces configured for positioning within the recessed surfaces, and radially opposite extending portions configured to block rotation between the compression insert and the receiver, the radially opposite extending portions having top surfaces configured to be positioned under a most bottom surface of the elongate rod when the elongate rod is received within the receiver channel,
wherein the compression insert is configured to be positioned within the receiver in a first position before the shank is uploaded, with the compression insert in the first position being inhibited from moving upwardly and downwardly within the central bore by at least partial engagement between the exterior surfaces of the compression insert and the recessed surfaces of the receiver, and
wherein the compression insert is configured to be downwardly displaced by a forced engagement into a second position within the central bore after capture of the upper end portion, the downward displacement causing a forced interference engagement between the exterior surfaces and inwardly-facing interference surfaces integrally formed into the interior surfaces of the receiver below the recessed surfaces so as to inhibit the compression insert from moving back up within the central bore.
15. The pivotal bone anchor assembly of claim 14 , wherein the compression insert is configured to be forcibly downwardly displaced by a first tool applying a force along the longitudinal axis of the receiver.
16. The pivotal bone anchor assembly of claim 15 , wherein the compression insert is configured to be upwardly retrieved from the forced interference engagement using a second tool so as to release the upper end portion from a friction fit angular orientation relative to the receiver.
17. The pivotal bone anchor assembly of claim 14 , wherein the upper end portion further comprises an at least partially spherical shape.
18. The pivotal bone anchor assembly of claim 14 , wherein the shank is cannulated along an entire length thereof.
19. The pivotal bone anchor assembly of claim 14 , wherein the pivotal bone anchor assembly is a polyaxial bone screw.
20. The pivotal bone anchor assembly of claim 14 , wherein the compression insert includes a central through bore.
21. The pivotal bone anchor assembly of claim 14 , further comprising a set screw top, and wherein the set screw includes a helically wound structure formed into an outer sidewall surface engageable with the helically wound structure to lock the elongate rod within the channel.
22. The pivotal bone anchor assembly of claim 21 , wherein the set screw includes a bottom opposite a top of the set screw, the bottom comprising an outer rim structure with a planar recessed bottom surface interior to the outer rim structure.
23. The pivotal bone anchor assembly of claim 14 ,
wherein the compression insert has central opening about a longitudinal axis, and
wherein an upper surface of the insert further comprises an upwardly open contact surface extending continuously between the central opening toward a most front end surface and a most back end surface of the radially opposite extending portions and without upwardly projecting ridges or protrusions, the contact surface being configured to provide a substantially straight and continuous engagement with the most bottom surface of the rod across the length thereof.
24. The pivotal bone anchor assembly of claim 23 , wherein the upwardly open contact surface has a upwardly open partially cylindrical shape configured to provide a substantially straight and continuous engagement with a lower portion of a cylindrically-shaped rod.