Modular polyaxial bone anchor with retainer having interconnected pieces
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a one-piece receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable, friction fit compression insert (some with lock and release feature), a down-loadable two-piece, interconnected retaining ring articulatable with respect to the receiver and an up-loadable shank upper portion cooperate to provide for assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra.
1 . A bone anchor comprising:
a) a shank having an elongate body and an upper portion, the body being configured for fixation to a bone;
b) a receiver having a top portion and a base, the receiver top portion defining a channel for receiving a longitudinal connecting member, the base having an internal seating surface partially defining a cavity, the channel communicating with the cavity, the cavity communicating with an exterior of the base through a receiver opening sized and shaped for upward loading of the shank upper portion through the receiver opening; and
c) a retainer having first and second discrete parts, the parts being attached to one another during loading of the retainer into the receiver, each retainer part having an inner surface and an outer surface, each inner surface configured for fixed engagement with the shank upper portion and each outer surface configured for sliding engagement with the receiver seating surface during pivoting of the shank with respect to the receiver, the retainer parts being detached from one another and each retainer part captured between the shank upper portion and the seating surface during pivoting of the shank with respect to the receiver, the parts cooperating to prevent the shank upper portion from passing down through the receiver opening, the parts being pressed away from one another during fixing of the shank at a desired angular orientation with respect to the receiver.
2 . The bone anchor of claim 1 further comprising a compression insert disposed within the receiver and configured to frictionally engage the shank upper portion at a location spaced from the retainer.
3 . The bone anchor of claim 2 wherein the insert is in a releasable frictional engagement with a portion of the receiver.
4 . The bone anchor of claim 2 wherein the insert has a pair of opposed upwardly extending arms, each arm having a pair of spaced recesses formed in an outer surface of the arm, the recesses sized and shaped for receiving inwardly crimped material from the receiver for prohibiting rotation of the insert with respect to the receiver.
5 . The bone anchor of claim 2 wherein the insert is sized and shaped to directly engage and cooperate with lock and release tools, the insert having a first tool receiving sloping surface positioned for alignment with a receiver second tool receiving sloping surface.
6 . The bone anchor of claim 1 further comprising a knob on the first retainer part and a groove on the second retainer part, the groove receiving a portion of the knob, and wherein during loading of the retainer into the receiver, the first and second retainer parts being attached to one another at an interface of the knob and the groove.
7 . The bone anchor of claim 6 wherein, after the first retainer part is detached from the second retainer part in the receiver, the knob portion remains received within the groove.
8 . The bone anchor of claim 1 wherein the first retainer part has a first top surface and the second retainer part has a second top surface, the first and second top surfaces being disposed at an angle with respect to one another when the retainer parts are attached to one another and the first and second top surfaces being substantially in a same plane when the parts are detached from one another.
9 . In a bone anchor, the improvement comprising:
a) a shank having a body for fixation to a bone and an integral upper portion having a first spherical surface;
b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a first surface partially defining a cavity, the channel communicating with the cavity;
c) at least one insert disposed within the receiver the insert having a concave surface frictionally mating with the shank first spherical surface;
d) a multi-piece interconnected retainer captured within the cavity, the pieces being movable and detachable while remaining interconnected, the pieces being positionable about at least a portion of the shank, the retainer having a concave surface for fixed engagement with the shank and a convex surface for unlocked slidable articulatable engagement with the receiver; and
e) wherein expansion-only locking engagement occurs between the shank upper portion and the retainer and between the retainer and the receiver.
10 . The improvement of claim 9 wherein the insert is in a releasable frictional engagement with a portion of the receiver.
11 . The improvement of claim 10 wherein the insert has a pair of opposed upwardly extending arms, each arm having a pair of spaced recesses formed in an outer surface of the arm, the recesses sized and shaped for receiving inwardly crimped material from the receiver for prohibiting rotation of the insert with respect to the receiver.
12 . The improvement of claim 11 wherein the insert is sized and shaped to directly engage and cooperate with lock and release tools, the insert having a first tool receiving sloping surface positioned for alignment with a receiver second tool receiving sloping surface.
13 . The improvement of claim 9 wherein the multi-piece retainer has first and second pieces and further comprises a knob on the first retainer piece and a groove on the second retainer piece, the groove receiving a portion of the knob, and wherein during loading of the retainer into the receiver, the first and second retainer pieces are attached to one another at an interface of the knob and the groove.
14 . The improvement of claim 13 wherein, the first retainer piece is detached from the second retainer piece in the receiver, the knob portion remaining received within the groove.
15 . The improvement of claim 13 wherein the first retainer piece has a first top surface and the second retainer piece has a second top surface, the first and second top surfaces being disposed at an angle with respect to one another when the retainer pieces are attached to one another and the first and second top surfaces being substantially in a same plane when the pieces are detached from one another.
16 . The improvement of claim 15 further comprising a tool cooperating with the first and second top surfaces, the tool sized and shaped to engage the first and second top surfaces and press the first and second top surfaces downwardly towards the receiver base, the tool pressing the first and second top surfaces into the substantially planar position and detaching the first and second retainer pieces.
17 . In a bone anchor, the improvement comprising:
a) a shank having a body for fixation to a bone and an integral upper portion having a first spherical surface;
b) a receiver having a top portion and a base, the receiver top portion defining an open channel, the base having a first surface partially defining a cavity, the channel communicating with the cavity, the receiver also having a first tool receiving sloping surface and through aperture;
c) at least one insert disposed within the receiver, the insert top loaded into the receiver channel and sized and shaped to directly engage and cooperate with lock and release tools, the insert having a second tool receiving sloping surface positioned for alignment with the receiver first tool receiving sloping surface; and
d) a multi-piece interconnected retainer captured within the cavity, the retainer being loadable into the receiver in an attached orientation and movable in a detached orientation to a position surrounding at least a portion of the shank, the retainer being fixed to the shank upper portion and articulatable with respect to the receiver when in an unlocked position, and wherein expansion-only locking engagement occurs between the shank upper portion and the retainer and between the retainer and the receiver.
18 . The improvement of claim 17 wherein the interconnected retainer has first and second discrete pieces fixed to one another during loading of the retainer into the receiver.
19 . The improvement of claim 18 wherein the first retainer piece has a curved convex projection and the second piece has a curved concave recess, the projection received within the recess and fixed to the second piece during loading of the retainer into the receiver, the projection detached from the second piece and received within the recess during pivoting of the projection within the recess during assembly of the retainer with the shank within the receiver cavity.