A bone anchor assembly for securing a rod to a bone of a patient via a closure top, the bone anchor assembly comprising:
- a receiver having a vertical axis, a lower body with a central bore formed around the vertical axis and communicating with a bottom of the receiver through a bottom opening, and a pair of opposed arms extending upward from the lower body defining a first channel having a transverse axis perpendicular to the vertical axis and configured to receive a portion of the rod, each arm including a pair of interior planar surfaces spaced apart from each other along opposite vertically extending perimeters of the arm, the central bore extending upwardly through the first channel to a top of the receiver and having a discontinuous helically wound thread integrally formed therein and interior opposed non-threaded partially-cylindrical recesses with downwardly-facing top surfaces integrally formed therein entirely below the helically wound thread, each partially-cylindrical recess and downwardly facing top surface thereof extending into and between a respective pair of the interior planar surfaces;
- a bone attachment structure having a body and an integral upper head portion with a partially spherical surface above a midline plane or hemisphere thereof, the upper head portion configured for positioning within the central bore of the receiver with the body extending through the bottom opening and pivotal with respect to the receiver;
- and
- an insert configured for top loading into the receiver, the insert having an insert body with upright insert arms forming a second channel configured to receive the portion of the rod when the insert is positioned within the receiver with the second channel aligned with the first channel, the insert arms having uppermost top surfaces having a partially-cylindrical outer edge configured to be entered into the partially-cylindrical recesses, the insert body further including a central through-and-through tool receiving opening centered about the vertical axis and oppositely-directed opposed extensions in the direction of the transverse axis configured to at least partially block rotation between the receiver and the insert, the opposed extensions having top surfaces that extend outwardly in the direction of the transverse axis and underneath a most bottom surface of the portion of the rod,
- wherein prior to the portion of the rod being positioned in the first and second channels and secured via the closure top, the uppermost top surfaces of the insert arms are configured to snap under and engage the downwardly-facing top surfaces of the opposed non-threaded recesses to establish a frictional non-floppy relationship between the bone attachment structure and the receiver and to prevent the insert from moving back up within the receiver.