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

A method of assembling a pivotal bone anchor assembly intended for securing an elongate rod to a bone of a patient with tooling, the method comprising:

• positioning a capture portion of a shank, a ring retainer, and a pressure insert into a receiver,
• the receiver comprising a vertical centerline axis, a base defining a cavity communicating with a bottom surface of the receiver through a bottom opening and including a lower circumferential groove adjacent the bottom opening having an upward-facing support surface, and a pair of spaced apart upright arms extending upward from the base to define a first open channel configured to receive the elongate rod, the cavity extending upward through the first open channel to define a central bore including a discontinuous and helically wound guide and advancement structure adjacent a top of the receiver, a discontinuous integral downward-facing surface below the guide and advancement structure, and a substantially cylindrical surface between the cavity and the discontinuous integral downward-facing surface including a vertically-aligned rotation abutment structure,
• the shank comprising the capture portion having a partial spherical surface and a central tool-engaging structure formed therein, and an anchor portion opposite the capture portion configured to fix to the bone, the capture portion being uploadable into the cavity of the receiver through the bottom opening,
• the ring retainer comprising an open ring body having outer surfaces and an inner surface, the ring retainer being uploadable into the lower circumferential groove through the bottom opening of the receiver after the capture portion with the outer surfaces being engaged with the upward-facing support surface of the lower circumferential groove and the inner surface being engaged with the capture portion so as to hold the capture portion within the cavity while allowing for pivotal movement between the receiver and the shank, and
• the pressure insert comprising a cylindrical body with upstanding arms, an upwardly-facing rod-receiving curvate surface extending between the upstanding arms to define a second open channel configured to receive the elongate rod, and a central opening configured to allow the tooling to pass through to engage the central tool-engaging structure of the shank, the upstanding arms having upwardly-facing surfaces located radially outward from the second open channel and outer side surfaces with a protruding rotational abutment structure formed therein, the pressure insert being positionable into the receiver into a first position adjacent the substantially cylindrical surface in which the central opening is centered on the vertical centerline axis of the receiver, the upwardly-facing surfaces on the upstanding arms are located adjacent to and angularly spaced from the discontinuous integral downward-facing surface, the second open channel is transverse to the first open channel, and the protruding rotational abutment structure is angularly spaced from the rotation abutment surface of the receiver;
• and
• rotating the pressure insert about the vertical centerline axis of the receiver until the second channel of the insert is aligned with the first channel of the receiver, the protruding rotational abutment structure of the pressure insert engages with the rotation abutment structure of the receiver to inhibit further rotation of the pressure insert in at least one direction, and the upwardly-facing surfaces on the upstanding arms rotate at least partially under the discontinuous integral downward-facing surface to inhibit the pressure insert from moving back up within the receiver.