Method of assembling a pivotal bone anchor assembly having a receiver and twist-in-place insert

A method of assembling a receiver assembly intended for use to secure an elongate rod to a capture head of a bone anchor that is implantable into a bone of a patient, the method comprising:

• positioning a retainer in a lower portion of a receiver, the receiver comprising an upper portion with an upper opening, a first channel configured to receive the elongate rod and extending downward from the upper opening, the lower portion having a bottom opening opposite the upper opening, and a through-space extending between the upper opening and the bottom opening, the through-space including at least one integral downward facing surface and at least one integral inwardly projecting surface formed therein prior to positioning the retainer in the receiver, the retainer configured to capture and pivotably secure the capture head of the bone anchor in the lower portion of the receiver;
• positioning an insert into the through-space of the receiver in a first orientation, the insert comprising one or more upward facing surfaces, one or more rotation alignment structures, and a second channel configured to receive the elongate rod simultaneous with the first channel of the receiver when the second channel is in alignment with the first channel, the second channel being non-aligned with the first channel when the insert is positioned in the first orientation;
• and
• rotating the insert in the through-space of the receiver from the first orientation to a second orientation in which the second channel is aligned with the first channel and the one or more upward facing surfaces of the insert is positioned under the at least one integral downward facing surface,
• wherein, after rotating the insert, the one or more rotation alignment structures come into a rotationally interfering arrangement with the at least one integral inwardly projecting surface of the receiver,
• wherein, after rotating the insert, the at least one integral downward facing surface and the one or more upward facing surfaces are initially configured to come into contact so as to limit the insert from moving towards the upper opening in the receiver, and
• wherein the rotationally interfering arrangement between the at least one integral inwardly projecting surface and the one or more rotation alignment structures maintains substantial alignment between the second channel and the first channel and inhibits further rotation of the insert relative to the receiver.