A method of assembling a receiver assembly of a bone anchor assembly for securing a rod to a bone, the method comprising:
- placing an insert into a receiver having a rod-receiving channel, the insert having a unitary-construction including a saddle surface, first engagement features adjacent the saddle surface, a downward-facing collet opposite the saddle surface, and rotation blocking extensions oriented in a direction of the receiver channel, the rotation blocking extensions blocking rotation between the insert and receiver when the insert is in the receiver, the rotation blocking extensions extending under a most bottom surface of the rod when the rod is received in the rod-receiving channel and against the saddle surface;
- and
- causing the insert to engage with the receiver in an upper engagement position that is above a lower engagement position, the receiver including an upper opening, a bottom opening opposite the upper opening, and a base cavity extending upward from the bottom opening, the rod-receiving channel extending downward from the upper opening and in communication with the base cavity to form a through space of the receiver extending between the upper opening and bottom opening, the receiver further including a discontinuous helically wound guide and advancement structure extending along an upper portion of the rod-receiving channel, upper engagement features in the through space and below the discontinuous helically wound guide and advancement structure, and lower engagement features in the through space, at least some of the lower engagement features being below the upper engagement features,
- wherein the upper engagement position includes at least some of the first engagement features abutting the upper engagement features as the saddle surface faces upward within the receiver and the collet faces downward within the receiver, and
- wherein the lower engagement position includes at least some of the first features abutting the lower engagement features as the saddle surface faces upward within the receiver and the collet faces downward within the receiver.