Pivotal bone anchor assembly insert with upright arms and rotation blocking extensions
A bone anchor assembly for securing an elongate rod to a bone of a patient includes a receiver having a central bore with interior opposed recesses having downwardly-facing top surfaces, and a shank with a head portion confiugred for positioning within the central bore with the body of the shank extending downwardly through a bottom opening. The assembly also includes an insert that is positionable into the central bore above the shank head, the insert including opposed extensions configured to inhibit rotation between the receiver and the insert, and upright arms having top surfaces complementary with the interior opposed recesses of the central bore. The top surfaces of the insert arms are configured to snap under and engage the downwardly-facing top surfaces of the interior opposed recesses so as to establish a frictional non-floppy relationship between the shank and the receiver and to prevent the insert from moving back up within the central bore.
1. A bone anchor assembly for securing a rod to a bone of a patient via a closure top, the bone anchor assembly comprising:
a receiver having a vertical axis, a lower body with a central bore formed around the vertical axis and communicating with a bottom of the receiver through a bottom opening, and a pair of opposed arms extending upward from the lower body defining a first channel having a transverse axis perpendicular to the vertical axis and configured to receive a portion of the rod, each arm including a pair of interior planar surfaces spaced apart from each other along opposite vertically extending perimeters of the arm, the central bore extending upwardly through the first channel to a top of the receiver and having a discontinuous helically wound thread integrally formed therein and interior opposed non-threaded partially-cylindrical recesses with downwardly-facing top surfaces integrally formed therein entirely below the helically wound thread, each partially-cylindrical recess and downwardly facing top surface thereof extending into and between a respective pair of the interior planar surfaces;
a bone attachment structure having a body and an integral upper head portion with a partially spherical surface above a midline plane or hemisphere thereof, the upper head portion configured for positioning within the central bore of the receiver with the body extending through the bottom opening and pivotal with respect to the receiver; and
an insert configured for top loading into the receiver, the insert having an insert body with upright insert arms forming a second channel configured to receive the portion of the rod when the insert is positioned within the receiver with the second channel aligned with the first channel, the insert arms having uppermost top surfaces having a partially-cylindrical outer edge configured to be entered into the partially-cylindrical recesses, the insert body further including a central through-and-through tool receiving opening centered about the vertical axis and oppositely-directed opposed extensions in the direction of the transverse axis configured to at least partially block rotation between the receiver and the insert, the opposed extensions having top surfaces that extend outwardly in the direction of the transverse axis and underneath a most bottom surface of the portion of the rod,
wherein prior to the portion of the rod being positioned in the first and second channels and secured via the closure top, the uppermost top surfaces of the insert arms are configured to snap under and engage the downwardly-facing top surfaces of the opposed non-threaded recesses to establish a frictional non-floppy relationship between the bone attachment structure and the receiver and to prevent the insert from moving back up within the receiver.
2. The bone anchor assembly of claim 1 , wherein the insert arms further include upper portions projecting radially outward near the uppermost top surfaces thereof, with the top surfaces of the radially-projecting upper portions defining the uppermost top surfaces of the insert engageable with the downwardly-facing top surfaces of the opposed non-threaded recesses.
3. The bone anchor assembly of claim 1 , wherein a width of the second channel at the level of the uppermost top surfaces of the insert arms, as measured perpendicular to both the transverse axis and the vertical axis, is greater than a diameter of the rod.
4. The bone anchor assembly of claim 1 , wherein a length of the second channel defined as the distance between outer ends of the opposed extensions, as measured along the transverse axis, is greater than the greatest width between inner surfaces of the insert arms, as measured perpendicular to both the transverse axis and the vertical axis.
5. The bone anchor assembly of claim 1 , wherein the uppermost top surfaces on the insert arms do not extend above a top of the rod when the portion of the rod is positioned within the first and second channels and the anchor bone assembly is in a locked configuration.
6. The bone anchor assembly of claim 1 ,
wherein the insert body and insert arms together form a saddle surface that defines a lower limit of the second channel, and
wherein top surfaces of the opposed extensions extend at least a portion of the saddle surface in the direction of the transverse axis so as to be underneath the portion of the rod positioned within the second channel.
7. The bone anchor assembly of claim 6 , wherein the top surfaces of the opposed extensions extend at least a portion of the saddle surface beyond an inner sidewall surface of the central bore of the receiver.
8. The bone anchor assembly of claim 1 , wherein the uppermost top surfaces of the insert arms are configured to be snapped into the opposed non-threaded recesses after the upper head portion of the bone attachment structure is disposed within the internal cavity.
9. The bone anchor assembly of claim 1 , wherein the insert arms have exterior surfaces with a maximum width therebetween and the opposed extensions have a maximum length, as measured along the transverse axis, that is greater than the maximum width.
10. The bone anchor assembly of claim 1 , wherein the top surfaces on the insert arms are configured to extend up to at least a maximum width or diameter of the rod when the most bottom surface of the portion of the rod is against the top surfaces on the opposed extensions.
11. The bone anchor assembly of claim 1 , wherein the insert body is above the upper head portion of the bone attachment structure so as to cooperate in providing a friction fit for the non-floppy relationship between the bone attachment structure and the receiver.
12. The bone anchor assembly of claim 1 , wherein the upper head portion of the bone attachment structure is engageable with a separate ring member positioned within the receiver cavity below the insert.
13. The bone anchor assembly of claim 12 , wherein the separate ring member is non-pivoting with respect to the receiver.
14. The bone anchor assembly of claim 12 , wherein the insert further includes a lower extending portion in the direction of the upper head portion and positioned above the separate ring member so as to provide a friction fit with respect to the bone attachment structure and the receiver.
15. The bone anchor assembly of claim 1 , wherein the bone attachment structure is cannulated.
16. The bone anchor assembly of claim 1 , wherein the bone attachment structure is configured for positioning within the central bore prior to the uppermost top surfaces of the insert being snapped under the downwardly-facing top surfaces of the opposed non-threaded recesses.
17. The bone anchor assembly of claim 1 , further comprising the closure top, wherein the closure top has a corresponding continuous helically wound thread engageable with the discontinuous helically wound thread of the central bore.
18. The bone anchor assembly of claim 17 , wherein the corresponding continuous helically wound thread is threadably engagable with the discontinuous helically wound thread, thereby advancing the closure top into the central bore upon rotation of the closure top relative to the receiver.
19. The bone anchor assembly of claim 17 , wherein the closure top is configured to abut the portion of the rod received in the first and second channels.
20. The bone anchor assembly of claim 17 , wherein the closure top remains spaced apart from the insert when the bone anchor assembly is in a locked configuration.
21. The bone anchor assembly of claim 17 , wherein the closure top includes an internal drive structure.
22. The bone anchor assembly of claim 17 , wherein the closure top includes a breakoff head.
23. The bone anchor assembly of claim 1 ,
wherein the discontinuous helically wound thread of the central bore is configured to inhibit the pair of opposed arms from splaying open at the top thereof when locked by the closure top.
24. The bone anchor assembly of claim 23 , wherein the pair of opposed arms include breakoff extensions.
25. The bone anchor assembly of claim 1 , wherein the discontinuous helically wound thread of the central bore of the receiver is a reverse angle thread.
26. The bone anchor assembly of claim 1 , wherein the receiver lower body below the first channel includes a front side surface opposite a back side surface, with each of the front and back side surfaces including a planar surface portion parallel with respect to each other and the vertical axis.
27. A bone anchor assembly for securing a rod to a bone of a patient via a closure top, the bone anchor assembly comprising:
a receiver having a vertical axis, a lower body with a central bore formed around the vertical axis and communicating with a bottom of the receiver through a bottom opening, and an upper portion integral with the lower body defining a first channel having a transverse axis perpendicular to the vertical axis and configured to receive a portion of the rod, the central bore extending upwardly through the first channel to a top of the receiver and having a discontinuous helically wound thread integrally formed therein and interior opposed non-threaded partially-cylindrical recesses with downwardly-facing top surfaces integrally formed therein entirely below the helically wound thread, each of the partially-cylindrical recesses and downwardly-facing top surfaces thereof extending from a first respective interior planar surface to a second respective interior planar surface spaced apart from the first respective interior planar surface, the first and second respective interior planar surfaces being substantially coplanar;
a bone attachment structure having a body and an integral upper head portion with a partially spherical surface above a midline plane or hemisphere thereof, the upper head portion configured for positioning within the central bore of the receiver with the body extending through the bottom opening and pivotal with respect to the receiver; and
an insert configured for top loading into the receiver, the insert having an insert body with upright insert arms forming a second channel configured to receive the portion of the rod when the insert is positioned within the receiver with the second channel aligned with the first channel, the insert arms having uppermost top surfaces having a partially-cylindrical outer edge configured to be entered into the partially-cylindrical recesses, the insert body further including a central through-and-through tool receiving opening centered about the vertical axis and oppositely-directed opposed extensions in the direction of the transverse axis configured to at least partially block rotation between the receiver and the insert, the opposed extensions having top surfaces that extend outwardly in the direction of the transverse axis and underneath a most bottom surface of the portion of the rod,
wherein prior to the portion of the rod being positioned in the first and second channels and secured via the closure top, the uppermost top surfaces of the insert arms are configured to snap under and engage the downwardly-facing top surfaces of the opposed non-threaded recesses to establish a frictional non-floppy relationship between the bone attachment structure and the receiver and to prevent the insert from moving back up within the receiver.