Pivotal bone anchor twist-in-place friction fit insert with side notches
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The upper portion expands a retaining member in the receiver cavity to capture the shank upper portion in the receiver. In some embodiment either the retaining member or an insert provide for a friction fit of the shank upper portion in the receiver resulting in non-floppy placement of the shank with respect to the receiver. Some retainers and inserts have a lock-and-release feature. Final locking of the polyaxial mechanism is provided by frictional engagement between the shank upper portion and the retaining member. A pre-assembled receiver, retaining member and optional insert may be popped-on or snapped-on to the shank upper portion prior to or after implantation of the shank into a vertebra.
1. A bone anchor assembly for securing a rod to a bone of a patient, the bone anchor assembly comprising:
a receiver including an upper opening, a bottom opening opposite the upper opening, a base cavity extending upward from the bottom opening, a rod-receiving channel extending downward from the upper opening and in communication with the base cavity to form a through space extending between the upper opening and bottom opening, a discontinuous helically wound guide and advancement structure extending along an upper portion of the rod-receiving channel, downward-facing engagement features formed in the through space and beneath the discontinuous helically wound guide and advancement structure, and a protrusion projecting radially inward from a surface of the through space; and
an insert configured for downloading into the through space through the upper opening, the insert having a saddle surface, top surfaces adjacent the saddle surface, outwardly-extending engagement features with upward-facing surfaces spaced below and radially offset relative to the top surfaces, and a recess or notch defined in an outer side of the insert having an outwardly facing surface spaced apart from the saddle surface,
wherein upon the insert being downloaded into the receiver through space, the insert is non-threadably rotatable within the through space to align the saddle surface with the rod-receiving channel, with the upward-facing surfaces rotating under and upwardly abutting the downward-facing engagement features to inhibit the insert from moving back upwardly within the receiver, and with the protrusion being received in the recess when the saddle surface is aligned with the rod-receiving channel, and
wherein the outwardly-extending engagement features of the insert are further configured to engage inner surfaces of the receiver through space to provide a releasable frictional engagement between the insert and the receiver.
2. The bone anchor assembly of claim 1 , wherein the protrusion being received in the recess or notch inhibits further rotation of insert within the receiver.
3. The bone anchor assembly of claim 1 , wherein the protrusion being received in the recess or notch forms a snap-fit engagement.
4. The bone anchor assembly of claim 1 , wherein the protrusion is a crimp wall.
5. The bone anchor assembly of claim 1 , wherein the outwardly-extending engagement features further comprises two outwardly-extending engagement features located opposite each other and the saddle surface is between the outwardly-extending engagement features.
6. The bone anchor assembly of claim 1 , wherein the radially-offset upward-facing surfaces further comprise two non-threaded surfaces located opposite each other.
7. The bone anchor assembly of claim 6 , wherein the non-threaded surfaces are substantially planar surfaces extending perpendicular to a longitudinal axis through the insert.
8. The bone anchor assembly of claim 1 , further comprising a retainer ring located in the base cavity.
9. The bone anchor assembly of claim 8 , wherein the retainer ring forms a discontinuous circular extent on account of a slot extending through the retainer ring.
10. The bone anchor assembly of claim 9 , wherein the retainer ring includes at least one recess defined in an outer circumferential surface of the retainer ring.
11. The bone anchor assembly of claim 8 , further comprising a bone attachment structure including a head and a body extending downwardly from the head, the head including a substantially spherical portion, wherein, when (1) the insert is inside the receiver and the saddle surface is aligned with the rod-receiving channel, (2) the head is received in the receiver such that the head upwardly contacts the insert and downwardly contacts the retainer ring, and (3) the outwardly-extending engagement features are engaged with the inner surfaces of the through space to provide the releasable frictional engagement between the insert and the receiver, the body extends through the bottom opening and the bone attachment structure is configured to articulate relative to the receiver in a frictional non-floppy relationship.
12. The bone anchor assembly of claim 11 , wherein the retainer ring is configured for positioning in the base cavity prior to the head being uploaded into the receiver via the bottom opening.
13. The bone anchor assembly of claim 12 , wherein the receiver base cavity is configured to allow for expansion of the retaining ring located therein when the head is uploaded into the receiver via the bottom opening so as to capture the head in the base cavity.
14. The bone anchor assembly of claim 11 , wherein the body can articulate relative to the retainer ring.
15. The bone anchor assembly of claim 1 , wherein the rod includes an arcuate outer surface and the saddle surface includes an arcuate surface that receives the arcuate outer surface.
16. The bone anchor assembly of claim 15 , wherein the arcuate outer surface includes a cylindrical outer surface.
17. The bone anchor assembly of claim 1 , further comprising a bone attachment structure and a closure, the bone attachment structure including a head and a body extending downwardly from the head, the head including a substantially spherical portion, wherein the closure is configured to mechanically interface with the discontinuous helically wound guide and advancement structure and be rotated downwardly along the discontinuous helically wound guide and advancement structure, driving the rod against the saddle surface to move the insert downwardly within the receiver, such that the upward-facing surfaces of the outwardly-extending engagement features stop being upwardly abutting against the downward-facing engagement features and the insert exerts force against the head sufficient to lock an orientation of the body relative to the receiver.
18. The bone anchor assembly of claim 17 , wherein the bone attachment structure body includes a helical thread extending along at least a portion thereof.
19. The bone anchor assembly of claim 17 , wherein the bone attachment structure further includes a cannulation extending along a length of the bone attachment structure.
20. The bone anchor assembly of claim 1 , wherein the insert further includes a central through-and-through tool receiving opening extending through the saddle surface.
21. The bone anchor assembly of claim 1 , wherein the insert includes rotation blocking features with respect to the receiver.
22. The bone anchor assembly of claim 1 , wherein the recess or notch defined in the outer side of the insert is in the form of a groove.
23. The bone anchor assembly of claim 1 , wherein the recess or notch defined in the outer side of the insert extends below the insert top surface.
24. The bone anchor assembly of claim 1 , wherein
the recess or notch defined in the outer side of the insert further comprises two recesses located on opposite locations on the outer side of the insert,
the protrusion further comprises two protrusions located on opposite locations of the surface of the through space, and
each protrusion is configured to be received in its respective recess after the saddle surface aligns with the rod-receiving channel so as to block further rotation of the insert in the receiver.
25. The bone anchor assembly of claim 1 , wherein the rod-receiving channel is formed between upright arms of the receiver, with each of the receiver upright arms having upwardly-extending break-off extensions.