Method of assembling a pivotable bone anchor assembly with independent locking by insert side compressing member

A method of assembling a pivotal bone anchor assembly intended for independent locking with a vertically-translating insert compressing member prior to securing an elongate rod to a bone of a patient;

• the method comprising:
• positioning a capture portion of a bone anchor and an insert within a central bore of a receiver, the receiver comprising a longitudinal axis, a base, and a pair of upstanding arms extending upwardly from the base with opposed interior surfaces defining an open channel configured for receiving the elongate rod, the opposed interior surfaces of the upstanding arms having a guide and advancement structure formed thereon, the base including a receiver cavity in communication with a bottom of the receiver through a lower opening and with the open channel to define the central bore centered about the longitudinal axis, the receiver cavity configured to receive the bone anchor, and at least one of the upstanding arms configured to slidably receive the insert compressing member, the bone anchor comprising the capture portion with a spherical outer surface and an anchor portion configured for fixation to the bone, the capture portion configured to be pivotally disposed within the receiver cavity with the bone anchor extending downward through the lower opening, the insert being positioned within the central bore of the receiver above the capture portion of the bone anchor;
• pressing continuously downward on the insert with the insert compressing member in a direction parallel with the longitudinal axis until the insert comes into a compressive contact with the spherical outer surface of the capture portion of the bone anchor so as to establish a pressable and releasable locking engagement of the bone anchor with respect to the receiver independent of a closure top;
• with the insert compressing member in a downward compression position, positioning the elongate rod within the open channel of the receiver;
• securing the closure top to the guide and advancement structure of the receiver above the elongate rod to establish a final locked configuration of the elongate rod and the pivotal bone anchor assembly;
• and
• with the closure top maintaining the elongate rod and pivotal bone anchor assembly together in the final locked configuration, slidably removing the insert compressing member from the receiver in the direction parallel with the longitudinal axis.