Method of assembling a pivotal bone anchor assembly with ring retainer and twist-in-place pressure insert

Abstract

A method of assembling a pivotal bone anchor assembly includes positioning a capture portion of a shank, a retainer, and an insert into a receiver. The receiver includes an internal cavity with a circumferential groove adjacent a bottom opening, a first channel with a discontinuous downward-facing surface below a guide and advancement structure, and an internal cylindrical surface with a fixed rotation abutment surface. The shank with a capture portion is uploadable through the bottom opening. The retainer is uploadable into the circumferential groove to engage and hold the capture portion within the cavity. The insert includes a cylindrical body with a second channel between upstanding arms and is positionable into the first channel with the second channel transverse to the first channel. The method further includes rotating the insert within the receiver until the second channel of the insert is aligned with the first channel of the receiver.