Pivotal bone anchor assembly with cannulated shank having a planar top surface surrounding an internal drive socket

A pivotal bone anchor assembly configured for implantation into a bone of a patient about a guide wire with a drive tool, and for securing a fixation rod to the bone with a closure configured to apply a downwardly-directed force to lock the assembly, the pivotal bone anchor assembly comprising:

• a receiver comprising a base portion defining an axial bore centered about a vertical centerline axis and an upper portion integral with the base portion defining a channel configured to receive the fixation rod, the axial bore communicating with a bottom of the receiver through a lower opening and extending upward through the channel to a top of the receiver, the axial bore including an internal support surface adjacent the lower opening and a guide and advancement structure adjacent a top of the receiver configured to mate with the closure;
• a shank comprising a longitudinal axis, an anchor portion at a distal end configured for fixation to the bone, and a proximal end portion configured for positioning within the axial bore of the receiver so as to be pivotally supported by the internal support surface with the shank extending downward through the lower opening, the proximal end portion including an upwardly-opening drive socket configured to mate with the drive tool and an upwardly-facing planar top surface perpendicular to the longitudinal axis surrounding and entirely peripheral to the drive socket, the shank including a central bore centered about the longitudinal axis and extending distally from the drive socket to a distal tip of the anchor portion and configured to receive the guide wire;
• a retainer positionable within the axial bore of the receiver and configured to capture and hold the proximal end portion of the shank within the axial bore with the shank extending downward through the lower opening, the retainer having a lower portion of an outer surface configured to engage the internal support surface of the axial bore with the shank having pivotal movement with respect to the receiver prior to the assembly being locked by the closure;
• and
• an insert positionable within the axial bore of the receiver having an upper surface configured to receive the fixation rod, a lower surface configured for overlapping engagement with an upper portion of the outer surface of the retainer, and a central aperture configured to provide access to the drive socket of the proximal end portion by the drive tool,
• wherein after assembly of the retainer, the proximal end portion of the shank, and the insert into the axial bore of the receiver, the planar top surface on the proximal end portion is configured to remain spaced apart from the lower surface of the insert so as to not directly receive the downwardly-directed force when the assembly is locked by the closure.