Pivotal bone anchor assembly with multi-part shank retainer and rod-engaging insert

A pivotal bone anchor assembly for securing a rod to a bone of a patient, the pivotal bone anchor assembly comprising:

• a shank having an elongate body, a driving tip and a capture structure, the elongate body disposed between the driving tip and the capture structure, the elongate body configured for fixation to the bone, the capture structure having a spherical upper region and a spherical lower region opposite the spherical upper region, the elongate body extending downwardly towards the driving tip from the spherical lower region;
• a receiver having a top portion and a base, the top portion defining an open channel configured to receive the rod, the base having an interior surface at least partially defining a cavity of the base, the open channel communicating with the cavity, the cavity communicating with an exterior of the base through a bottom opening in the base, the bottom opening being sized and shaped to receive the capture structure of the shank therethrough;
• and
• a retainer structure having first and second retainer pieces, the first retainer piece having a first inner surface and a first outer surface, the second retainer piece having a second inner surface and a second outer surface, the first and second inner surfaces configured for frictional engagement with the capture structure and the first and second outer surfaces configured for frictional engagement with the interior surface that at least partially defines the cavity of the base, the first and second retainer pieces configured to hold the capture structure in the cavity of during angular positioning of the shank relative to the receiver,
• wherein the first and second retainer pieces are positionable within the cavity prior to the capture structure.

A pivotal bone anchor assembly for securing a rod to a bone of a patient, the pivotal bone anchor assembly comprising:

• a shank having an elongate body and a capture structure, the elongate body being configured for fixation to the bone;
• a receiver having a top portion and a base, the receiver top portion defining a channel to receive the rod, the base having a non-cylindrical internal surface partially defining a cavity, the channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening configured to upward load the capture structure of the shank through the opening;
• and
• a retainer structure having at least two discrete retainer parts, each retainer part having an inner surface and an outer surface, the inner surface configured to be in frictional engagement with the capture structure and the outer surface configured to be in frictional engagement with the non- cylindrical internal surface when the capture structure is captured by the retainer structure, the retainer parts cooperating to prevent the shank capture structure from exiting the receiver cavity through the opening,
• wherein the retainer structure is configured for pivotal movement with respect to the receiver prior to the pivotal bone anchor assembly being locked by a closure.

A pivotal bone fixation assembly for securing a fixation rod to a bone of a patient, the pivotal bone fixation assembly comprising:

• a bone fastener having a head and a bone-engaging portion;
• a receiver defining a central through space along a first axis for receiving the bone fastener at a variable angle, the receiver having a non-cylindrical inner surface in a lower portion of the receiver adjacent a bottom opening of the through space;
• and
• a retainer with at least two discrete retainer parts positionable in the receiver lower portion, each retainer part having a planar top surface perpendicular to a second axis of the retainer and an inclined surface with respect to the planar top surface so as to provide clearance space for the at least two retainer parts to pivot relative to each other when installing the head of the bone fastener into the retainer within the receiver through the bottom opening of the receiver through space.

A pivotal bone fixation assembly for securing a rod to a bone of a patient, the pivotal bone fixation assembly comprising:

• a bone fastener having a head and a bone-engaging portion;
• a receiver defining an opening along a first axis for receiving the bone fastener at a variable angle, the receiver having an inner articulation surface at a lower portion of the opening;
• and
• first and second retainer parts configured to be coupled to the bone fastener head for movement therewith, the first and second retainer parts bcing configured to be matingly articulable with the inner articulation surface of the receiver, with at least one retainer part including a notch for receiving a portion of the other retainer part during assembly of the first and second parts with the bone fastener head in the receiver.