Pivotal bone anchor assembly having a restrained pre-loaded shank head retainer

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 receiver comprising a lower portion defining an internal chamber communicating with a bottom of the receiver through a bottom opening, and an upper portion defining a channel configured to receive the elongate rod, the internal chamber communicating with the channel to define a central bore and including a lower region adjacent the bottom opening and an upper region adjacent to and above the lower region, the central bore including a discontinuous guide and advancement structure configured to mate with a closure top and at least one downward-facing abutment surface preformed therein between the discontinuous guide and advancement structure and the upper region of the internal chamber;
• a bone anchor comprising a capture portion and an anchor portion opposite the capture portion configured for attachment to the bone, the capture portion positionable in the internal chamber of the receiver with the bone anchor extending downward through the bottom opening;
• and
• a retainer configured to be positioned and restrained from upward movement in the upper region of the internal chamber prior to the capture portion of the bone anchor, the retainer including an upper portion defining an uppermost surface and configured to extend above the capture portion of the bone anchor when the capture portion is positioned in the internal chamber of the receiver,
• wherein the retainer in the upper region is configured to expand about the capture portion of the bone anchor upon its uploading through the bottom opening so as to receive and capture the capture portion within the internal chamber, and
• wherein the retainer is thereafter downwardly displaceable toward the lower region of the internal chamber via engagement by the tooling to move at least one upward-facing surface of the retainer below the at least one downward-facing abutment surface of the central bore so as to inhibit the retainer from moving back up into the upper region of the internal chamber.