Pivotal bone anchor assembly with forcibly downwardly displaceable pressure insert
A pivotal bone anchor assembly includes a bone anchor having a proximal capture portion and an anchor portion, and a receiver having a channel for receiving a rod, an internal cavity with upper expansion and lower locking regions, and a central bore with an inwardly-protruding circumferentially-extending interference engagement structure. The assembly also includes a pressure insert having an upper surface for engaging the rod and an exterior surface for engaging the interference engagement structure to restrict movement of the pressure insert within the central bore. After the proximal capture portion of the bone anchor is positioned within internal cavity, the pressure insert is downwardly movable within the central bore to force the exterior surface at least partially past the interference engagement structure to inhibit the pressure insert from moving back up within the central bore.
1 . A pivotal bone anchor assembly intended for securing an elongate rod to a bone of a patient with tooling, the pivotal bone anchor assembly comprising:
a bone anchor having a proximal portion with an at least partially spherical outer surface and an integral anchor portion extending distally from the proximal portion configured for attachment to the bone;
a receiver comprising a base defining an internal cavity in communication with a bottom surface of the base through a bottom opening, and a pair of integral upright arms extending upwardly from the base to define an open channel configured to receive the elongate rod, the internal cavity having an upper expansion region and a lower locking region below the upper expansion region defined by a narrower width of the internal cavity adjacent the bottom opening, the internal cavity communicating with the open channel to define a central bore including a discontinuous guide and advancement structure adjacent a top of the receiver configured to mate with a closure and an inwardly-protruding circumferentially-extending interference engagement structure below the discontinuous guide and advancement structure;
a pressure insert positionable within the central bore of the receiver, the pressure insert comprising an upper seat surface sized and shaped for engaging the elongate rod and an exterior surface configured for overlapping engagement with an upper portion of the interference engagement structure of the receiver to inhibit downward movement of the pressure insert within the central bore,
wherein after the proximal portion of the bone anchor is positioned within the internal cavity of the receiver and prior to the elongate rod being received in the open channel, the pressure insert is configured for forced downward displacement within the central bore by the tooling until the exterior surface of the pressure insert is forced at least partially past the interference engagement structure to inhibit the pressure insert from moving back up within the central bore.
2 . The pivotal bone anchor assembly of claim 1 and further comprising a separate retainer positionable within the internal cavity of the receiver before the bone anchor, the retainer comprising:
a lower portion with at least one slit formed through a thickness thereof; and
an upper portion configured to contact a downward-facing lower planar surface of the pressure insert,
wherein upward movement of the retainer during an uploading of the proximal portion of the bone anchor through the bottom opening is restricted by the contact between the upper portion of the retainer and the lower planar surface of the pressure insert; and
wherein the lower portion of the retainer is configured to expand within the expansion portion of the internal cavity to receive the proximal portion of the bone anchor as it is uploaded through the bottom opening, and then to close around and capture the proximal portion within the internal cavity while allowing for pivotal motion of the bone anchor relative to the receiver.
3 . The pivotal bone anchor assembly of claim 2 , wherein the retainer is non-pivoting with respect to the receiver after capturing the proximal portion of the bone anchor.
4 . The pivotal bone anchor assembly of claim 2 , wherein the retainer is configured to be held in the upper expansion region of the internal cavity prior to capturing the proximal portion of the bone anchor.
5 . The pivotal bone anchor assembly of claim 1 , wherein the pressure insert is positionable within the central bore of the receiver before the bone anchor.
6 . The pivotal bone anchor assembly of claim 1 , wherein the pressure insert is configured to be top-loaded into the receiver.
7 . The pivotal bone anchor assembly of claim 1 , wherein the bone anchor is cannulated, with an axial bore extending an entire length thereof from a distal tip of the anchor portion to a proximal end surface of the proximal portion.
8 . The pivotal bone anchor assembly of claim 1 , wherein the interference engagement structure of the central bore and the exterior surface of the pressure insert in the downwardly displaced position have a non-overlapping interference fit engagement with respect to each other.
9 . The pivotal bone anchor assembly of claim 1 , wherein the pressure insert is configured to be non-threadably rotated into its initial position within the central bore of the receiver.
10 . The pivotal bone anchor assembly of claim 1 , wherein the closure is configured for positioning entirely within the open channel of the receiver above the elongate rod and in engagement with the discontinuous guide and advancement structure of the upright arms 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.
11 . The pivotal bone anchor assembly of claim 1 , wherein the interference engagement structure of the central bore is non-resilient.
12 . A pivotal bone anchor assembly intended for securing an elongate rod to a bone of a patient with tooling, the pivotal bone anchor assembly comprising:
a bone anchor having a proximal portion with an at least partially spherical outer surface and an integral anchor portion extending distally from the proximal portion configured for attachment to the bone;
a receiver comprising a base defining an internal cavity in communication with a bottom surface of the base through a bottom opening, and a pair of integral upright arms extending upwardly from the base to define an open channel configured to receive the elongate rod, the internal cavity having an upper expansion region and a lower locking region below the upper expansion region defined by a narrower width of the internal cavity adjacent the bottom opening, the internal cavity communicating with the open channel to define a central bore including a discontinuous guide and advancement structure adjacent a top of the receiver configured to mate with a closure and an inwardly-protruding circumferentially-extending interference engagement structure below the discontinuous guide and advancement structure;
a separate retainer positionable within the internal cavity of the receiver before the bone anchor, the retainer comprising a lower portion with at least one slit formed through a thickness thereof; and an upper portion configured to contact a downward-facing lower planar surface of the pressure insert;
a pressure insert positionable within the central bore of the receiver before the bone anchor, the pressure insert comprising an upper seat surface sized and shaped for engaging the elongate rod and an exterior surface configured for overlapping engagement with an upper portion of the interference engagement structure of the receiver to inhibit downward movement of the pressure insert within the central bore,
wherein after the proximal portion of the bone anchor is captured within the lower portion of the retainer and prior to the elongate rod being securely locked in the open channel via the closure, the pressure insert is configured for forced downward displacement within the central bore by the tooling until the exterior surface of the pressure insert is forced at least partially past the interference engagement structure to inhibit the pressure insert from moving back up within the central bore.
13 . The pivotal bone anchor assembly of claim 12 ,
wherein upward movement of the retainer during an uploading of the proximal portion of the bone anchor through the bottom opening is restricted by the contact between the upper portion of the retainer and the lower planar surface of the pressure insert; and
wherein the lower portion of the retainer is configured to expand within the expansion portion of the internal cavity to receive the proximal portion of the bone anchor as it is uploaded through the bottom opening, and then to close around and capture the proximal portion within the internal cavity while allowing for pivotal motion of the bone anchor relative to the receiver.
14 . The pivotal bone anchor assembly of claim 12 , wherein the retainer is non-pivoting with respect to the receiver after capturing the proximal portion of the bone anchor.
15 . The pivotal bone anchor assembly of claim 12 , wherein the retainer is configured to be held in the upper expansion region of the internal cavity prior to capturing the proximal portion of the bone anchor.
16 . The pivotal bone anchor assembly of claim 12 , wherein the pressure insert is configured to be top-loaded into the receiver.
17 . The pivotal bone anchor assembly of claim 12 , wherein the bone anchor is cannulated along an entire length thereof from a distal tip of the anchor portion to a proximal end surface of the proximal portion.
18 . The pivotal bone anchor assembly of claim 12 , wherein the interference engagement structure of the central bore and the exterior surface of the pressure insert in the downwardly displaced position have a non-overlapping interference fit engagement with respect to each other.
19 . The pivotal bone anchor assembly of claim 12 , wherein the pressure insert is configured to be non-threadably rotated into its initial position within the central bore of the receiver.
20 . The pivotal bone anchor assembly of claim 12 , wherein the closure is configured for positioning entirely within the open channel of the receiver above the elongate rod and in engagement with the discontinuous guide and advancement structure of the upright arms 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.
21 . The pivotal bone anchor assembly of claim 12 , wherein the interference engagement structure of the central bore is non-resilient.