Tool compressed insert for closure independent locking of a pivotal bone anchor assembly

A pivotal bone anchor assembly for securing an elongate rod to a bone with a closure via closure independent locking with an insert compressing tool, the pivotal bone anchor assembly comprising:

• a receiver having a base defining a cavity communicating with a bottom opening, and a pair of upright arms extending upwardly from the base to define an open channel for receiving the elongate rod, the open channel communicating with the cavity to define a central bore, the pair of upright arms including:
• opposed inward-facing surfaces having a discontinuous helically wound closure-mating structure formed therein;
• and
• outward-facing surfaces having receiver tool engagement structures formed therein for releasable overlapping engagement with the insert compressing tool;
• a bone anchor having a capture portion pivotally disposed within the receiver cavity and an anchor portion extending distally from the capture portion and through the receiver bottom opening for fixation to the bone;
• and
• a compression insert at least partially disposed within the receiver center bore and having an upper surface configured for engagement with the elongate rod, the insert having a central opening and upward-facing surfaces on tool engagement structures positioned radially outward from the central opening,
• wherein the the receiver tool engagement structures and the insert upward-facing tool engagement structures are configured for simultaneous non-threadable engagement and downward compressing engagement, respectively, by the insert compressing tool, thereby applying a downward force to independently lock a position of the bone anchor with respect to the receiver prior to securing the elongate rod within the receiver open channel via the closure, and
• wherein the closure is positionable within the channel while the position of the bone anchor with respect to the receiver is so independently locked by the insert compressing tool.