Uniplanar bone anchor assembly
A pivotal uniplanar bone anchor assembly includes a shank having a shank head with a partial spherical shape at a proximal end and an anchor portion opposite the shank head for fixation to the bone of a patient. The assembly also includes a receiver having a top portion defining an open channel for receiving an elongate rod and a base defining a cavity in communication with the open channel and with a bottom surface of the receiver through a distal opening. The assembly further includes a retainer positionable into non-pivotal engagement with an inner surface of the cavity prior to the shank head being received within the cavity, with the retainer having a central passage configured to receive and support the shank head within the cavity while restricting pivotal motion between the shank and the receiver to a single plane.
1. A uniplanar bone anchor assembly for securing an elongate rod to a bone of a patient with a closure top, the uniplanar bone anchor assembly comprising:
a shank having a shank head at a proximal end and a unitary anchor portion opposite the shank head configured for fixation to the bone, the shank head having a partial spherical shape with a flat planar outer surface portion on at least one side;
a receiver having a longitudinal axis, a top portion with upwardly extending arms defining an open channel configured for receiving the elongate rod, and a base defining a cavity in communication with the open channel and having a distal opening in communication with a bottom surface of the base, the upwardly extending arms having opposed internal surfaces extending between a front side surface and a back side surface and including a mating structure formed therein and configured for mating with the closure top, the cavity including an inner groove extending at least partially circumferentially around the cavity; and
a retainer having a central opening configured to receive the shank head, an outer surface sized and shaped for insertion into and non-pivotal engagement with the inner groove of the cavity of the receiver, a thickness between the outer surface and an inner surface, a vertical slot or gap extending through the thickness thereof configured to allow for compression of the retainer during installation of the retainer into the cavity, the vertical slot or gap separating two ends of the retainer adjacent the slot or gap into a non-overlapping arrangement, and at least one flat planar inner surface portion configured to contact the flat planar outer surface portion of the shank head so as to restrict a pivotal motion of the shank relative to the receiver to only one plane,
wherein the inner groove and the retainer are configured together such that the retainer is positioned in the inner groove in a fixed predetermined rotational alignment orientation with respect to the longitudinal axis of the receiver.
2. The uniplanar bone anchor assembly of claim 1 , wherein the flat planar outer surface portion of the shank head is spaced from and parallel with a longitudinal axis of the shank.
3. The uniplanar bone anchor assembly of claim 1 ,
wherein the shank head includes flat planar outer surface portions on two substantially opposite sides that are parallel with respect to each other, and
wherein the retainer includes two opposing flat planar inner surface portions configured to contact the two flat planar outer surface portions of the shank head.
4. The uniplanar bone anchor assembly of claim 1 ,
wherein the inner groove has a width greater than a width of the distal opening.
5. The uniplanar bone anchor assembly of claim 1 , wherein the mating structure of the receiver further comprises a discontinuous helically wound guide and advancement structure.
6. The uniplanar bone anchor assembly of claim 1 , wherein the retainer includes outer planar surface cuts on opposite sides of the slot or gap configured for cooperating with complementary alignment structures formed into the inner groove.
7. The uniplanar bone anchor assembly of claim 1 ,
wherein retainer is configured to be top loaded into the receiver.
8. The uniplanar bone anchor assembly of claim 1 , further comprising a pressure insert configured to engage the elongate rod, and wherein the pressure insert is configured to be positioned between the shank head and the elongate rod when the elongate rod is installed into the bone anchor assembly.
9. The uniplanar bone anchor assembly of claim 1 , wherein the pressure insert is configured to be top loaded into the receiver.
10. The uniplanar bone anchor assembly of claim 1 , wherein the shank head includes an internal tool mating drive socket.
11. The uniplanar bone anchor assembly of claim 1 , wherein the shank is cannulated along an entire length thereof.
12. The uniplanar bone anchor assembly of claim 1 , wherein the at least one flat planar inner surface portion of the retainer is configured to contact the flat planar outer surface portion of the shank head when the shank head is uploaded through the distal opening of the receiver.
13. A uniplanar bone anchor assembly for securing an elongate rod to a bone of a patient with a closure top, the uniplanar bone anchor assembly comprising:
a shank having a shank head at a proximal end and a unitary anchor portion opposite the shank head configured for fixation to the bone, the shank head having a partial spherical shape;
a receiver having a top portion with upwardly extending arms defining an open channel configured for receiving the elongate rod, and a base defining a cavity in communication with the open channel and having a distal opening in communication with a bottom surface of the base, the upwardly extending arms including a mating structure formed therein and configured for mating with the closure top; and
a retainer having an outer surface sized and shaped for non-pivotal engagement with an inner surface of the cavity of the receiver prior to the shank head being received therein and a central passage configured to receive the shank head when the shank head is uploaded through the distal opening,
wherein the retainer is configured to restrict relative pivotal motion between the shank and the receiver to a single plane.
14. The uniplanar bone anchor assembly of claim 13 , wherein the shank head includes an internal tool mating drive socket.
15. The uniplanar bone anchor assembly of claim 13 , wherein the shank head is configured to be bottom loaded into the cavity of the receiver through the distal opening.
16. The uniplanar bone anchor assembly of claim 13 , wherein the shank is cannulated along an entire length thereof.
17. The uniplanar bone anchor assembly of claim 13 , wherein the distal opening of the receiver is substantially round.
18. The uniplanar bone anchor assembly of claim 13 , wherein the mating structure of the receiver further comprises a discontinuous helically wound guide and advancement structure.
19. The uniplanar bone anchor assembly of claim 13 , wherein the retainer further comprises a thickness between the outer surface and an inner surface and a vertical slot or gap extending through the thickness thereof configured to allow for compression of the retainer during installation of the retainer into the cavity of the receiver.
20. The uniplanar bone anchor assembly of claim 13 , wherein the retainer includes outer planar surface cuts on opposite sides of the slot or gap configured for cooperating with complementary alignment structures formed into the inner groove.
21. The uniplanar bone anchor assembly of claim 13 , wherein the retainer is configured to be top loaded into the receiver.
22. The uniplanar bone anchor assembly of claim 13 , further comprising a pressure insert configured to engage the elongate rod, and wherein the pressure insert is configured to be positioned between the shank head and the elongate rod when the elongate rod is installed into the bone anchor assembly.
23. The uniplanar bone anchor assembly of claim 22 , wherein the pressure insert is configured to be top loaded into the receiver into a predetermined alignment orientation with respect to the longitudinal axis of the receiver.
24. The uniplanar bone anchor assembly of claim 13 , wherein the shank head includes a flat planar outer surface portion on at least one side.
25. The uniplanar bone anchor assembly of claim 24 , wherein the flat planar outer surface portion of the shank head is parallel with respect to the channel of the receiver when the shank head is engaged with the retainer.
26. The uniplanar bone anchor assembly of claim 24 , wherein the shank head includes a pair of flat planar outer surface portions.
27. The uniplanar bone anchor assembly of claim 13 , wherein the cavity of the receiver and the retainer are configured together such that the retainer is positioned in the cavity in a fixed predetermined rotational alignment orientation with respect to the longitudinal axis of the receiver.
28. The uniplanar bone anchor assembly of claim 13 , wherein the cavity of the receiver further comprises an inner groove extending at least partially circumferentially around the cavity.
29. The uniplanar bone anchor assembly of claim 28 , wherein the inner groove of the cavity and the retainer are configured together such that the retainer is positioned in the inner groove in a fixed predetermined rotational alignment orientation with respect to the longitudinal axis of the receiver.
30. The uniplanar bone anchor assembly of claim 19 , wherein the vertical slot or gap separates two ends of the retainer adjacent the slot or gap into a non-overlapping arrangement.