Pivotal bone anchor assembly having a threaded shank head and a threaded receiver lower opening

1. A pivotal spinal screw assembly for securing an elongate rod to a bone of a patient via a closure, the pivotal spinal screw assembly comprising:

a shank comprising a longitudinal axis, a capture portion, an anchor portion opposite the capture portion configured for fixation to the bone, and a neck portion extending between the capture portion and the anchor portion having a radius that is less than a radius of the capture portion and a radius of the anchor portion, the capture portion having an upper end including a counter-sunk tool engagement structure centered on the longitudinal axis and an annular linearly tapered surface surrounding the tool engagement structure, a curvilinear lower surface extending upwardly and outwardly from the neck portion, and a side outer surface extending between the curvilinear lower surface and the linearly tapered surface having a first guide and advancement structure formed therein; and

a head member comprising a base defining a lower portion of a central bore centered around a vertical centerline axis and configured to receive the capture portion, and an upper portion defining a channel configured to receive the elongate rod, the central bore communicating with a bottom of the base through a lower opening, extending upwards through the channel to a top of the head member, and having a reduced cross-section adjacent the lower opening configured to prevent the capture structure from exiting the central bore through the lower opening, the lower opening having a second guide and advancement structure formed therein and threadably mateable with the first guide and advancement structure,

wherein at least the curvilinear lower surface of the capture portion is configured for pivotal engagement with an internal surface on the reduced cross-section when the capture portion is disposed within the lower portion of the central bore, with the shank extending downward through the lower opening, so as to provide for pivotal angular movement of the shank relative to the head member prior to a locking of the pivotal spinal screw assembly via the closure.

2. The pivotal spinal screw assembly of claim 1 , wherein the internal surface on the reduced cross-section of the central bore is rounded.

3. The pivotal spinal screw assembly of claim 1 , wherein the internal surface on the reduced cross-section of the central bore is curvilinear.

4. The pivotal spinal screw assembly of claim 1 , wherein both the curvilinear lower surface and the first guide and advancement structure of the side outer surface of the capture portion are configured for pivotal engagement with an internal surface on the reduced cross-section of the central bore of the head member.

5. The pivotal spinal screw assembly of claim 1 , wherein the tool engagement structure further comprises an internal drive socket extending inward from the upper end of the capture portion and configured to receive a tool to drive the shank into the bone.

6. The pivotal spinal screw assembly of claim 5 , wherein the internal drive socket includes a plurality of internal tool engagement faces extending parallel to the longitudinal axis and downward to a planar seating surface extending perpendicular to the longitudinal axis.

7. The pivotal spinal screw assembly of claim 1 , further comprising a cannulation opening extending a length of the shank along the longitudinal axis of the shank.

8. The pivotal spinal screw assembly of claim 7 , wherein the cannulation opening has a constant diameter extending at least along the anchor portion of the shank.

9. The pivotal spinal screw assembly of claim 7 , wherein the cannulation opening is unthreaded at least along the anchor portion of the shank.

10. The pivotal spinal screw assembly of claim 1 , wherein the curvilinear lower surface, the side outer surface, and the linearly tapered upper surface of the capture portion together define a rounded enlargement shape of the capture portion configured for positioning within the lower portion of the central bore of the head member.

11. The pivotal spinal screw assembly of claim 1 , further comprising a mating structure formed into an upper portion of the central bore and configured to mate with the closure.

12. The pivotal spinal screw assembly of claim 11 and further comprising the elongate rod and the closure, wherein the closure is configured for positioning entirely within the upper portion of the central bore of the head member above the elongate rod and in engagement with the mating structure to apply a downward pressure to a top of the elongate rod received within the channel, so as to secure the elongate rod to the bone of the patient.

13. The pivotal spinal screw assembly of claim 12 , wherein the linearly tapered surface of the capture portion of the shank is configured to be spaced apart from the elongate rod when the elongate rod is received within the channel of the head member and secured with the closure.

14. The pivotal spinal screw assembly of claim 12 ,

wherein the upper portion of the head member further comprises a pair of upright arms extending upward from the base portion to define the channel configured to receive the elongate rod, and

wherein the mating structure further comprises a discontinuous helically wound guide and advancement structure configured to inhibit splaying of the upright arms.

15. A method of assembling a pivotal spinal screw assembly configured to secure an elongate rod to a bone of a patient via a closure, the method comprising:

introducing a capture portion of a shank having a first guide and advancement structure into a lower opening of a head member having a second guide and advancement structure such that the first and second guide and advancement structures cooperate to allow the capture portion to pass through the lower opening, the head member including a base defining a lower portion of a central bore communicating with a bottom of the base through the lower opening and an upper portion defining a channel configured to receive the elongate rod, the central bore extending upwards through the channel to a top of the head member and having a reduced cross-section adjacent the lower opening configured to prevent the capture structure from exiting the central bore through the lower opening;

passing the capture portion of the shank entirely through the lower opening into the lower portion of the central bore, the shank including a longitudinal axis and an anchor portion opposite the capture portion configured for fixation to the bone with a neck portion between the capture portion and the anchor portion defined by a circumferential concave surface having a radius that is less than a radius of the capture portion and a radius of the anchor portion, the capture portion including an upper end including a counter-sunk tool engagement structure centered on the longitudinal axis and an annular linearly tapered surface surrounding the tool engagement structure, a curvilinear lower surface extending upwardly and outwardly from the neck portion, and a side outer surface extending between the curvilinear lower surface and the linearly tapered surface having the first guide and advancement structure formed therein; and

establishing a pivotable arrangement between the shank and the head member with at least the curvilinear lower surface of the capture portion of the shank in pivotal engagement with an internal surface on the reduced cross-section of the central bore, with the shank extending downward through the lower opening, so as to provide for pivotal angular movement of the shank relative to the head member prior to a locking of the pivotal spinal screw assembly via the closure.

16. The method of claim 15 , wherein passing the capture portion entirely through the lower opening into the internal cavity includes rotatably uploading the capture portion through the lower opening.

17. The method of claim 16 , wherein rotatably uploading the capture portion entirely through the lower opening into the internal cavity includes threading the capture portion through the lower opening.