Pivotal bone anchor assembly with forcibly downwardly displaceable pressure insert

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 bone anchor having a proximal portion with an at least partially spherical outer surface and an integral anchor portion extending distally from the proximal portion configured for attachment to the bone;
• a receiver comprising a base defining an internal cavity in communication with a bottom surface of the base through a bottom opening, and a pair of integral upright arms extending upwardly from the base to define an open channel configured to receive the elongate rod, the internal cavity having an upper expansion region and a lower locking region below the upper expansion region defined by a narrower width of the internal cavity adjacent the bottom opening, the internal cavity communicating with the open channel to define a central bore including a discontinuous guide and advancement structure adjacent a top of the receiver configured to mate with a closure and an inwardly-protruding circumferentially-extending interference engagement structure below the discontinuous guide and advancement structure;
• a separate retainer positionable within the internal cavity of the receiver before the bone anchor, the retainer comprising a lower portion with at least one slit formed through a thickness thereof;
• and an upper portion configured to contact a downward-facing lower planar surface of the pressure insert;
• a pressure insert positionable within the central bore of the receiver before the bone anchor, the pressure insert comprising an upper seat surface sized and shaped for engaging the elongate rod and an exterior surface configured for overlapping engagement with an upper portion of the interference engagement structure of the receiver to inhibit downward movement of the pressure insert within the central bore,
• wherein after the proximal portion of the bone anchor is captured within the lower portion of the retainer and prior to the elongate rod being securely locked in the open channel via the closure, the pressure insert is configured for forced downward displacement within the central bore by the tooling until the exterior surface of the pressure insert is forced at least partially past the interference engagement structure to inhibit the pressure insert from moving back up within the central bore.