Pivotal bone anchor assembly with twist-in-place insert

A pivotal bone anchor assembly configured for arrangement with a tool prior to securing an elongate rod to a bone of a patient via a closure, the pivotal bone anchor assembly comprising:

• a receiver having a base defining a bottom opening, an upper portion defining an open channel configured to receive the elongate rod, and an axial bore centered around a longitudinal axis, the axial bore communicating with a bottom of the receiver through the bottom opening and extending upwardly through the open channel to a top of the receiver, the axial bore including a discontinuous guide and advancement structure mateable with the closure proximate the top of the receiver and at least one downward-facing shoulder surface pre-formed therein between the discontinuous guide and advancement structure and the bottom opening;
• a shank having an anchor portion configured for fixation to the bone and an integral capture portion opposite the anchor portion configured for positioning into the axial bore of the receiver with the shank extending downward through the bottom opening;
• and
• a pressure insert having at least one upward-facing contact surface, the pressure insert configured for downloading into the axial bore of the receiver into a first position and for subsequent rotation about the longitudinal axis by the tool into a second position that locates the at least one upward-facing contact surface under the at least one downward-facing shoulder surface to inhibit the pressure insert from moving back up within the axial bore of the receiver.

A pivotal bone anchor assembly configured for arrangement with a tool prior to securing an elongate rod to a bone of a patient via a closure, the pivotal bone anchor assembly comprising:

• a receiver having a base defining a bottom opening, an upper portion defining an open channel configured to receive the elongate rod, and an axial bore centered around a longitudinal axis, the axial bore communicating with a bottom of the receiver through the bottom opening and extending upwardly through the open channel to a top of the receiver, the axial bore including a discontinuous guide and advancement structure mateable with the closure proximate the top of the receiver and a pair of opposed downward-facing shoulder surfaces pre-formed therein between the discontinuous guide and advancement structure and the bottom opening;
• a shank having an anchor portion configured for fixation to the bone and an integral capture portion opposite the anchor portion configured for positioning into the axial bore of the receiver with the shank extending downward through the bottom opening;
• a retainer configured for positioning into the axial bore of the receiver prior to the capture portion of the shank;
• and
• a pressure insert having upward-facing contact surfaces extending radially outward from a central body, the pressure insert configured for downloading into the axial bore of the receiver into a first position and for subsequent rotation about the longitudinal axis by the tool into a second position that locates the upward-facing contact surfaces at least partially under the downward-facing shoulder surfaces to prevent the pressure insert from moving back up within the axial bore of the receiver,
• wherein the retainer is operable to expand about the capture portion of the shank during an uploading of the capture portion into the axial bore through the bottom opening so as to capture and hold the capture portion within the receiver and in spaced relation with respect to an interior surface of the axial bore, the retainer having an outer surface engageable with the interior surface of the axial bore to allow for pivotal motion between the receiver and the shank in an unlocked configuration.