Polyaxial pedicle screw assembly with cannulated screw shank having an internal drive socket surrounded by a planar top end surface

A polyaxial pedicle screw assembly intended for securing an elongate rod to a bone of a patient, the pivotal bone screw assembly comprising:

• a receiver comprising a lower portion defining an internal cavity in communication with a bottom surface of the receiver through a bottom opening, and an upper portion defining a channel configured to receive the elongate rod, the internal cavity communicating with the channel to define a central bore having a mating structure at an upper end configured to mate with a closure top and a curved seating surface adjacent the bottom opening;
• a screw shank comprising a longitudinal axis, a shank head at a proximal end having an outer spherical surface with a single common radius defining a hemisphere plane at a maximum width perpendicular to the longitudinal axis, an anchor portion at a distal end configured for fixation to the bone, and a neck extending between the shank head and the anchor portion, the shank head including an upper portion defined by the outer spherical surface extending above the hemisphere plane toward an annular planar top end surface extending perpendicular to the longitudinal axis and entirely surrounding an internal drive socket formed into a top end of the shank head, and a lower portion defined by the outer spherical surface extending below the hemisphere plane toward the neck, the screw shank including a central opening extending from the internal drive socket entirely through the neck and the anchor portion to a distal tip thereof, and the shank head being configured for positioning within the internal cavity of the receiver, with the screw shank extending downward through the bottom opening, and with the outer spherical surface of the lower portion of the shank head in slidable engagement with the curved seating surface so as to establish pivotable motion between the screw shank and the receiver in an unlocked configuration;
• an insert at least partially positionable within the channel of the receiver and having an upper surface configured to receive the elongate rod and a lower surface configured to engage the outer spherical surface of the upper portion of the shank head so as to direct a downwardly-directed force from the elongate rod to the screw shank to lock a position of the screw shank relative to the receiver in a locked configuration,
• wherein the annular planar top end surface on the shank head is configured to remain spaced apart from the lower surface of the insert so as to not directly receive the downwardly-directed force therefrom in the locked configuration.