Method of assembling a pivotal bone anchor assembly with press-in-place insert

A method of assembling a pivotal bone anchor assembly configured to secure an elongate rod to a bone of a patient via a closure top, the method comprising:

• positioning an upper portion of a bone screw and a ring shaped structure with a central opening into a central bore of a receiver,
• the receiver comprising a base defining a lower portion of the central bore communicating with a bottom surface of the receiver through a lower opening, and a first pair of upright arms extending upward from the base to define a first open channel configured to receive the elongate rod, the central bore extending upwards from the lower opening through the first open channel to tops of the upright arms and including a discontinuous and helically wound guide and advancement structure adjacent the tops of the upright arms configured for rotatable engagement with the closure top, a seating surface adjacent the lower opening, and at least one internal retaining recess between the seating surface and the guide and advancement structure, and
• the bone screw comprising the upper portion and a threaded lower anchor portion opposite the upper portion, the upper portion having a partial spherical lower surface extending radially outward and axially upward from the threaded lower anchor portion and configured to provide for pivotal motion of the bone screw with respect to the receiver;
• positioning an insert into the central bore of the receiver open channel, the insert comprising a substantially-cylindrical insert body slidably having a bottom surface configured to transfer a downward compressive force from the closure top to lock the pivotal bone anchor assembly, and a second pair of upright arms extending upward from the insert body to define a second open channel extending between a front face and a back face of the insert and configured to receive the elongate rod, the second pair of upright arms including laterally-outward-facing surfaces and upwardly-facing surfaces extending between the front face and the back face of the insert;
• and
• pressing the insert into position within the central bore such that the upwardly-facing surfaces on the second pair of upright arms are positioned at least partially under a downwardly-facing surface of the at least one internal retaining recess so as to inhibit upward movement of the insert within the receiver.