A pivotal bone anchor assembly intended for securing an elongate rod to a bone of a patient, the pivotal bone anchor assembly comprising:
- a receiver comprising a base portion defining a cavity in communication with a bottom of the receiver through a bottom opening, and an upper portion having a pair of upright arms extending upward from the base portion to define an open channel configured to receive the elongate rod, the open channel opening upwardly onto top surfaces on the upright arms and opening transversely outwardly onto front and back outer surfaces of the upright arms, the cavity communicating with the open channel to define a central bore centered about a vertical centerline axis and extending upwardly from the bottom opening to the top surfaces of the upright arms, the upright arms further including:
- a discontinuous helically wound guide and advancement structure integrally formed into the central bore adjacent the top surfaces of the upright arms;
- opposed circumferentially-extending and downward-facing insert abutment surfaces integrally formed into the central bore below the guide and advancement structure;
- side outer surfaces opposite the central bore;
- and
- a non-threaded tool engagement recess extending horizontally at least partially around the side outer surface of each upright arm and opening onto the front and back surfaces of each of the upright arms, each tool engagement recess being isolated from the central bore and located below the top surface of the respective upright arm;
- a shank comprising a proximal capture portion configured for positioning within the cavity of the receiver and having an at least partially-spherical upper surface, and a distal anchor portion opposite the proximal capture portion configured for attachment to the bone;
- a pressure insert configured for positioning within the central bore of the receiver, the pressure insert comprising:
- a body with a centralized through-bore configured to receive a driving tool;
- a downwardly-facing bottom surface surrounding the through-bore and being sized and shaped to frictionally engage and mate with the partially-spherical upper surface of the proximal capture portion;
- and
- an upwardly facing curvate surface formed into an upper portion of the pressure insert and configured to receive the elongate rod;
- and
- a closure top configured for positioning entirely within the central bore of the receiver above the elongate rod and in engagement with the guide and advancement structure to apply a downward pressure to a top of the elongate rod, so as to secure the elongate rod to the bone of the patient,
- wherein the opposed circumferentially-extending and downward-facing insert abutment surfaces are configured for engagement by opposite circumferentially-extending and upward-facing surfaces of the pressure insert, upon positioning of the proximal capture portion of the shank into the cavity of the receiver, to prohibit upward movement of the pressure insert out of the receiver.