Bone anchor assembly with a downwardly displaceable twist-in-place insert

A pivotal bone anchor assembly intended for securing an elongate rod to bone of a patient, 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 and in communication with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base having interior faces defining a first open channel configured to receive the elongate rod, the central bore extending upward from the bottom opening through the first open channel to tops of the upright arms and including a discontinuous guide and advancement structure extending along an upper portion of the first open channel, a discontinuous upper groove beneath the discontinuous guide and advancement structure, a discontinuous lower groove between the discontinuous upper groove and the bottom opening, and a discontinuous engagement surface between the discontinuous upper groove and the discontinuous lower groove, the interior faces of the first open channel including U-shaped inward-facing end surfaces on either side of the central bore that define front and back ends of the first open channel, both the discontinuous upper groove and the discontinuous lower groove extending circumferentially around the central bore to open into the U-shaped inward-facing end surfaces;
• a bone anchor comprising a capture head having an at least partially spherical outer surface and an anchor portion opposite the capture head implantable into the bone of the patient, the capture head being positionable into the lower portion of the central bore with the bone anchor extending downward through the bottom opening;
• and
• an insert comprising a second open channel configured to receive the elongate rod, top surfaces adjacent the second channel, opposite side structures protruding laterally outward with arcuate planar topside surfaces spaced entirely below the top surfaces of the insert, and a curvate lower surface configured to engage the capture head of the bone anchor, the insert configured for loading into a non-aligned position within the central bore of the receiver with the second open channel being in non-alignment with the first open channel,
• wherein the insert further comprises upstanding insert arms defining the second open channel, the upstanding insert arms including planar end surfaces defining front and back faces of the second open channel,
• wherein the opposite side structures further comprise arcuate insert ridges extending entirely around outer side surfaces of the upstanding insert arms between the planar end surfaces,
• wherein the insert is rotatable in the central bore of the receiver from the non-aligned position to an aligned position so as to align the second open channel with the first open channel and to rotate the opposite side structures into openings in the U-shaped inward-facing end surfaces defined by the discontinuous upper groove and through to an overlapping arrangement within the discontinuous upper groove with the opposite side structures being adjacent to and above the discontinuous engagement surface, and
• wherein upon a forced downward displacement of the insert within the central bore of the receiver, the opposite side structures of the insert are configured to move slidably fictionally across the discontinuous engagement surface of the central bore and snap into the discontinuous lower groove so as to inhibit the insert and the bone anchor from moving upward within the receiver.

A method of assembling a receiver assembly used to secure an elongate rod to a capture head of a bone anchor that is implantable into a bone of a patient, the method comprising:

• aligning an insert with a receiver such that a second open channel of the insert is in non-alignment with a first open channel of the receiver, the first and second open channels being configured to receive the elongate rod when the second open channel is in alignment with the first open channel;
• loading the insert into a central bore of the receiver with the second open channel in a non-aligned position with the first open channel, the receiver comprising a base defining a lower portion of the central bore centered about a vertical centerline axis and in communication with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base having interior faces defining the first open channel, the central bore extending upward from the bottom opening through the first open channel to tops of the upright arms and including a discontinuous guide and advancement structure extending along an upper portion of the first open channel, a discontinuous upper groove beneath the discontinuous guide and advancement structure, a discontinuous lower groove between the discontinuous upper groove and the bottom opening, and a discontinuous cylindrical engagement surface between the discontinuous upper groove and the discontinuous lower groove, the interior faces of the first open channel including U-shaped inward-facing end surfaces on either side of the central bore that define front and back ends of the first open channel, both the discontinuous upper groove and the discontinuous lower groove extending circumferentially around the central bore to open into the U-shaped inward-facing end surfaces, the insert comprising top surfaces adjacent the second channel, opposite side structures protruding laterally outward and with arcuate planar topside surfaces spaced entirely below the top surfaces of the insert, and a curvate lower surface configured to engage an upper portion of the capture head of the bone anchor;
• and
• rotating the insert in the central bore of the receiver from the non-aligned position to an aligned position so as to align the second open channel with the first open channel and to rotate the opposite side structures into openings in the U-shaped inward-facing end surfaces defined by the discontinuous upper groove and through to an overlapping arrangement within the discontinuous upper groove with the opposite side structures being adjacent to and above the discontinuous cylindrical engagement surface,
• wherein upon a forced downward displacement of the insert within the central bore of the receiver, the opposite side structures are configured to move slidably fictionally across the discontinuous cylindrical engagement surface of the central bore and snap into the discontinuous lower groove so as to inhibit the insert from moving upward within the receiver.

A method of assembling a pivotal bone anchor assembly used to secure an elongate rod to a bone of a patient, the method comprising:

• aligning an insert with a receiver such that a second open channel of the insert is in a non-alignment with a first open channel of the receiver, the first and second open channels being configured to receive the elongate rod when the second open channel is in alignment with the first open channel;
• loading the insert into a central bore of the receiver with the second open channel in a non-aligned position with the first open channel, the receiver comprising a base defining a lower portion of the central bore centered about a vertical centerline axis and in communication with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base having interior faces defining the first open channel, the central bore extending upward from the bottom opening through the first open channel to tops of the upright arms and including a discontinuous guide and advancement structure extending along an upper portion of the first open channel, a discontinuous upper groove beneath the discontinuous guide and advancement structure, a discontinuous lower groove between the discontinuous upper groove and the bottom opening, and a discontinuous engagement surface between the discontinuous upper groove and the discontinuous lower groove, the interior faces of the first open channel including U-shaped inward-facing end surfaces on either side of the central bore that define front and back ends of the first open channel, both the discontinuous upper groove and the discontinuous lower groove extending circumferentially around the central bore to open into the U-shaped inward-facing end surfaces, the insert comprising top surfaces adjacent the second channel, opposite side structures protruding laterally outward with arcuate planar topside surfaces spaced entirely below the top surfaces of the insert, and a curvate lower surface configured to engage an upper portion of a capture head of a bone anchor captured within the lower portion of the central bore with the bone anchor extending downward through the bottom opening;
• rotating the insert in the central bore of the receiver from the non-aligned position to an aligned position so as to align the second open channel with the first open channel and to rotate the opposite side structures into openings in the U-shaped inward-facing end surfaces defined by the discontinuous upper groove and through to an overlapping arrangement within the discontinuous upper groove with the opposite side structures being adjacent to and above the discontinuous engagement surface;
• uploading the capture head of the bone anchor into the lower portion of the central bore through the bottom opening, the bone anchor comprising the capture head having an at least partially spherical outer surface and an anchor portion opposite the capture head implantable into the bone of the patient;
• and
• forcibly displacing the insert downwardly within the central bore of the receiver until the opposite side structures move slidably fictionally across the discontinuous engagement surface and snap into the discontinuous lower groove so as to inhibit the insert from moving upward within the receiver.

A receiver assembly intended for securing an elongate rod to a capture head of a bone anchor that is implantable into a bone of a patient, the receiver assembly comprising:

• a receiver comprising a base defining a lower portion of a central bore centered about a vertical centerline axis and in communication with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base having interior faces defining a first open channel configured to receive the elongate rod, the central bore extending upward from the bottom opening through the first open channel to tops of the upright arms and including a discontinuous guide and advancement structure extending along an upper portion of the first open channel, a discontinuous upper groove beneath the discontinuous guide and advancement structure, a discontinuous lower groove between the discontinuous upper groove and the bottom opening, and a discontinuous cylindrical engagement surface between the discontinuous upper groove and the discontinuous lower groove, the interior faces of the first open channel including U-shaped inward-facing end surfaces on either side of the central bore that define front and back ends of the first open channel, both the discontinuous upper groove and the discontinuous lower groove extending circumferentially around the central bore to open into the U-shaped inward-facing end surfaces;
• an insert comprising a second open channel configured to receive the elongate rod, top surfaces adjacent the second channel, opposite side structures protruding laterally outward with arcuate planar topside surfaces spaced entirely below the top surfaces of the insert, and a curvate lower surface configured to engage an upper portion of the capture head of the bone anchor, the insert configured for loading into a non-aligned position within the central bore of the receiver with the second open channel being in non-alignment with the first open channel;
• and
• a retainer positionable into the lower portion of the central bore and configured to capture and pivotably secure the capture head of the bone anchor within the base of the receiver,
• wherein the insert is rotatable in the central bore of the receiver from the non-aligned position to an aligned position so as to align the second open channel with the first open channel and to rotate the opposite side structures into openings in the U-shaped inward-facing end surfaces defined by the discontinuous upper groove and through to an overlapping arrangement within the discontinuous upper groove, with the opposite side structures being adjacent to and above the discontinuous cylindrical engagement surface, and
• wherein upon a forced downward displacement of the insert within the central bore of the receiver, the opposite side structures of the insert are configured to move slidably fictionally across the discontinuous cylindrical engagement surface of the central bore and snap into the discontinuous lower groove so as to inhibit the insert from moving upward within the receiver.

A pivotal bone anchor assembly intended for securing an elongate rod to bone of a patient, 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 and in communication with a bottom of the base through a bottom opening, and a pair of upright arms extending upward from the base having interior faces defining a first open channel configured to receive the elongate rod, the central bore extending upward from the bottom opening through the first open channel to tops of the upright arms and including a discontinuous guide and advancement structure extending along an upper portion of the first open channel, a discontinuous upper groove beneath the discontinuous guide and advancement structure, a discontinuous lower groove between the discontinuous upper groove and the bottom opening, and a discontinuous engagement surface between the discontinuous upper groove and the discontinuous lower groove, the interior faces of the first open channel including U-shaped inward-facing end surfaces on either side of the central bore that define front and back ends of the first open channel, both the discontinuous upper groove and the discontinuous lower groove extending circumferentially around the central bore to open into the U-shaped inward-facing end surfaces;
• a bone anchor comprising a capture head having an at least partially spherical outer surface and an anchor portion opposite the capture head implantable into the bone of the patient, the capture head being positionable into the lower portion of the central bore with the bone anchor extending downward through the bottom opening;
• an insert comprising a second open channel configured to receive the elongate rod, top surfaces adjacent the second channel, opposite side structures protruding laterally outward with arcuate planar topside surfaces spaced entirely below the top surfaces of the insert, and a curvate lower surface configured to engage the capture head of the bone anchor, the insert configured for loading into a non-aligned position within the central bore of the receiver with the second open channel being in non-alignment with the first open channel;
• and
• a retainer positionable into the lower portion of the central bore and configured to capture and pivotably secure the capture head of the bone anchor within the base of the receiver,
• wherein the insert is rotatable in the central bore of the receiver from the non-aligned position to an aligned position so as to align the second open channel with the first open channel and to rotate the opposite side structures into openings in the U-shaped inward-facing end surfaces defined by the discontinuous upper groove and through to an overlapping arrangement within the discontinuous upper groove with the opposite side structures being adjacent to and above the discontinuous engagement surface, and
• wherein upon a forced downward displacement of the insert within the central bore of the receiver, the opposite side structures of the insert are configured to move slidably fictionally across the discontinuous engagement surface of the central bore and snap into the discontinuous lower groove so as to inhibit the insert and the bone anchor from moving upward within the receiver.