Pivotal bone anchor assembly with non-pivoting, non-rotatable retainer
A pivotal 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 an upper portion defining a channel for receiving an elongate rod and a base defining a cavity in communication with the channel and with a bottom surface of the receiver through a distal opening. The assembly further includes a retainer positionable into non-rotatable and 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 opening configured to receive and capture the shank head within the cavity while allowing for pivotal motion between the shank and the receiver in at least one plane, and with a lower portion of the retainer extending below the bottom surface of the receiver.
1. A pivotal bone anchor assembly for securing an elongate rod to a bone of a patient with a closure top, the pivotal bone anchor assembly comprising:
a shank comprising a shank head at a proximal end having a partial spherical shape and a unitary anchor portion opposite the shank head configured for fixation to the bone;
a receiver comprising a vertical centerline axis, a base defining a cavity in communication with a bottom surface of the receiver through a distal opening, and upright arms extending upward from the base with opposed internal surfaces extending between a front side surface and a back side surface of the receiver to define an open channel configured to receive the elongate rod, the open channel in communication with the cavity, the internal surfaces of the upwardly extending arms including a guide and advancement structure configured for mating with the closure top, the cavity including an upward-facing planar support surface above the distal opening and a first pair of parallel planar alignment surfaces defining alignment planes that are parallel to and laterally offset from the vertical centerline axis; and
a retainer positionable into the cavity and comprising a central axis, an outer surface, and an inner surface defining a central opening configured to receive and capture the shank head, a thickness between the outer surface and the inner surface, at least one vertical slot or gap extending through at least a portion of the thickness so as to allow for expansion of the retainer during an uploading of the shank head into the retainer, a downward-facing surface, and a second pair of parallel planar alignment surfaces complementary with the first pair of parallel planar alignment surfaces, the retainer configured for capturing the shank head within the cavity of the receiver with the downward-facing surface in non-pivotal engagement with the upward-facing planar support surface, the second pair of parallel planar alignment surfaces in engagement with the first pair of parallel planar alignment surfaces, and a lower portion of the retainer extending below the bottom surface of the receiver;
wherein the first pair of parallel planar alignment surfaces and the second pair of second alignment surfaces are cooperatively configured to maintain the retainer in a fixed predetermined rotational alignment orientation with respect to the vertical centerline axis of the receiver during pivotal motion of the shank relative to the receiver and the retainer.
2. The pivotal bone anchor assembly of claim 1 , wherein the retainer and receiver are cooperatively configured so as to allow the retainer to be uploaded into the cavity through the distal opening of the receiver.
3. The pivotal bone anchor assembly of claim 1 , wherein the retainer and receiver are cooperatively configured so as to allow the retainer to be downwardly displaced along the vertical centerline axis of the receiver into the fixed predetermined rotational alignment orientation.
4. The pivotal bone anchor assembly of claim 1 , wherein the guide and advancement structure of the receiver further comprises a discontinuous helically wound guide and advancement structure.
5. The pivotal bone anchor assembly of claim 1 , wherein the retainer is compressible.
6. The pivotal bone anchor assembly of claim 1 , wherein the retainer and receiver are cooperatively configured for at least a partial non-pivotal slidable engagement therebetween prior to securing the elongate rod on the open channel of the receiver with the closure top.
7. The pivotal bone anchor assembly of claim 1 , wherein the retainer further includes at least one cut-out surface formed into the central opening and configured to provide for increased angulation of the shank relative to the receiver in the direction of the at least one cut-out surface.
8. The pivotal bone anchor assembly of claim 1 and further comprising a pressure insert configured to engage the elongate rod,
wherein the pressure insert and receiver are cooperatively configured to allow the pressure insert to be positioned between the shank head and the elongate rod when the elongate rod is installed into the pivotal bone anchor assembly.
9. The pivotal bone anchor assembly of claim 8 , wherein the pressure insert and receiver are cooperatively configured to allow the pressure insert to be top loaded into the receiver.
10. The pivotal bone anchor assembly of claim 1 , wherein the shank head includes an internal tool mating drive socket.
11. The pivotal bone anchor assembly of claim 1 , wherein the shank is cannulated with an axial bore centered about a longitudinal axis of the shank and extending along an entire length thereof.
12. A method of assembling a pivotal bone anchor assembly configured to secure an elongate rod to a bone of a patient with a closure top, the method comprising:
loading a retainer into a cavity formed into a base portion of a receiver, the cavity communicating with a bottom surface of the receiver through a distal opening, the receiver further including a vertical centerline axis and an upper portion defining a channel extending between a front side surface and a back side surface of the receiver and configured to receive the elongate rod, the channel communicating with the cavity and including opposed internal surfaces with a guide and advancement structure formed therein configured for mating with the closure top, the cavity including an upward-facing planar support surface above the distal opening and a first pair of parallel planar alignment surfaces defining alignment planes that are parallel to and laterally offset from the vertical centerline axis; and
positioning the retainer in the cavity in a fixed predetermined rotational alignment orientation with respect to the vertical centerline axis of the receiver by non-pivotal engagement of a second pair of parallel planar alignment surfaces of the retainer with the first pair of parallel planar alignment surfaces of the cavity, the retainer further including a central axis, an outer surface, an inner surface defining a central opening configured to receive and capture a shank head of a shank, a thickness between the outer surface and the inner surface, and at least one vertical slot or gap extending through at least a portion of the thickness to allow for expansion of the retainer during an uploading of the shank head into the central opening of the retainer, after which the retainer is configured to close around and capture the shank head, and with a downward facing surface of the retainer in non-pivotal engagement with the upward-facing planar support surface of the cavity and with a lower portion of the retainer extending downward below the bottom surface of the receiver.
13. The method of claim 12 , wherein positioning the retainer in the cavity includes bottom loading the retainer into the cavity through the distal opening.
14. The method of claim 12 , wherein positioning the retainer in the cavity includes top loading the retainer into the cavity through the channel.
15. The method of claim 12 , further comprising downwardly displacing the retainer along the vertical centerline axis of the receiver into the fixed predetermined rotational alignment orientation within the cavity.
16. The method of claim 12 , further comprising:
uploading the shank head into the cavity of the receiver through the central opening of the retainer;
positioning the elongate rod in the channel and into engagement with an upper surface of the shank head; and
installing the closure top into the channel above the elongate rod to apply downward pressure to the elongate rod so as to lock the pivotal bone anchor assembly, wherein installing the closure top includes threadably mating the closure top with the guide and advancement structure formed into the opposed internal surfaces of the channel via tightening of male and female helically wound flange forms.
17. The method of claim 12 , further comprising positioning a pressure insert configured to engage the elongate rod into the channel of the receiver such that the pressure insert will be positioned between the shank head and the elongate rod when the elongate rod is installed into the pivotal bone anchor assembly and the shank head is received in the cavity of the receiver.
18. The method of claim 17 , wherein, in positioning the pressure insert in the channel of the receiver, the pressure insert is top loaded into the receiver.
19. The method of claim 17 , further comprising uploading the shank head into the cavity of the receiver through the central opening of the retainer and into engagement with a lower surface of the pressure insert.
20. The method of claim 19 , further comprising:
positioning the elongate rod in the channel and into engagement with an upper surface of the pressure insert; and
installing the closure top into the channel above the elongate rod to apply downward pressure to the elongate rod so as to lock the pivotal bone anchor assembly, wherein installing the closure top includes threadably mating the closure top with the guide and advancement structure formed into the opposed internal surfaces of the channel via a tightening of male and female helically wound flange forms.