Pivotal bone anchor assembly with receiver having tool engagement grooves and increased shank angulation
A pivotal bone screw assembly includes a receiver having a base defining a lower portion of a central bore, and an upper portion extending upward from the base to define a channel configured to receive an elongate rod. The upper portion further includes a guide and advancement structure proximate a top end configured for engagement with a closure top, and side outer surfaces with tool engagement grooves extending horizontally and circumferentially to the front and back faces of the receiver. The assembly further includes a shank having a head and an anchor portion configured for attachment to the bone, with the head being positionable into the central bore of the receiver with the shank extending downward through the lower opening. The lower opening is configured to provide for increased pivotal movement of the shank with respect to the receiver in at least one direction.
1. A pivotal bone anchor assembly for securing an elongate rod to a bone of a patient via a closure top, the pivotal bone anchor assembly comprising:
a receiver comprising:
a base defining a lower portion of a central bore centered about a vertical centerline axis of the receiver and communicating with a bottom surface of the receiver through a lower opening; and
an upper portion extending upward from the base with opposed internal surfaces extending between a front face and a back face of the receiver to define a channel configured to receive the elongate rod, the central bore extending upward through the upper portion to a top of the receiver and including a guide and advancement structure configured for engagement with the closure top, the upper portion including:
side outer surfaces opposite the internal surfaces and extending downward across the base toward the bottom surface of the receiver; and
non-threaded curvate tool engagement grooves extending horizontally and circumferentially across the side outer surfaces below the top of the receiver to at least one of the front face and the back face; and
a shank comprising a head and an anchor portion opposite the head configured for attachment to the bone, the head having an at least partial spherical shape defining a hemisphere plane perpendicular to a longitudinal axis of the shank and at a maximum width along the longitudinal axis, and being positionable into the lower portion of the central bore of the receiver with the shank extending downward through the lower opening, the shank being pivotable with respect to the receiver in an unlocked configuration,
wherein the lower opening is configured to provide for increased pivotal movement of the shank with respect to the receiver in at least one direction when the head of the shank is received within the lower portion of the central bore of the receiver.
2. The pivotal bone anchor assembly of claim 1 , wherein the lower opening of the base of the receiver includes a curvate cut-out surface sized and shaped for providing clearance for an increased angle of articulation between the shank and the receiver.
3. The pivotal bone anchor assembly of claim 1 , wherein the central bore of the receiver includes a non-threaded internal recess with a downwardly-facing surface between the lower opening and the guide and advancement structure.
4. The pivotal bone anchor assembly of claim 3 and further comprising an insert, the insert having an outer portion configured for positioning at least partially within the internal recess of the central bore with an upper surface engageable with the downwardly-facing surface so as to inhibit upward movement of the insert within the central bore.
5. The pivotal bone anchor assembly of claim 4 , wherein the internal recess is formed into the central bore of the receiver before the insert is positioned into the central bore.
6. The pivotal bone anchor assembly of claim 4 , wherein the insert further comprises an inwardly- and downwardly-opening curvate surface configured to engage the head of the shank above the hemisphere plane thereof when the vertical centerline axis of the receiver is aligned with the longitudinal axis of the shank.
7. The pivotal bone anchor assembly of claim 1 , wherein the upper portion of the receiver further comprises upright arms extending upward from the base to define the channel, each of the upright arms including a break-off extension extending upwardly from a top of the upright arm that exists when the break-off extension is no longer attached to the upright arm.
8. The pivotal bone anchor assembly of claim 1 , further comprising a retaining structure separate from the receiver and configured to capture and hold the head of the shank within the lower portion of the central bore.
9. The pivotal bone anchor assembly of claim 8 , wherein the retaining structure includes a rounded interior seating surface configured to engage the head of the shank when the head of the shank is captured and held within the lower portion of the central bore.
10. The pivotal bone anchor assembly of claim 9 , wherein the rounded interior seating surface of the retaining structure is configured to engage the head of the shank above and below the hemisphere plane thereof.
11. The pivotal bone anchor assembly of claim 1 , wherein the shank includes a cannulation through bore extending the entire length of the shank along the longitudinal axis thereof.
12. The pivotal bone anchor assembly of claim 1 , further comprising the elongate rod and the closure top, wherein the closure top is configured for positioning within the central bore of the receiver above the elongate rod and in engagement with the guide and advancement structure to apply a downward pressure to a top of the elongate rod, so as to secure the elongate rod to the bone of the patient.
13. The pivotal bone anchor assembly of claim 1 and further comprising an insert, the insert being positionable within the central bore of the receiver and engageable with the head of the shank so as to provide a friction fit that inhibits pivotal movement of the shank with respect to the receiver prior to the pivotal bone anchor assembly being locked by the closure top.