Pivotal bone anchor assembly with receiving member having a collet, pressure insert, and slidable outer sleeve

A pivotal bone anchor assembly for securing an elongate rod to a head of a shank via a closure top, the pivotal bone anchor assembly comprising:

• a shank comprising a head and an anchor portion opposite the head configured for attachment to a bone of a patient;
• a receiving member comprising:
• a central bore centered about a vertical centerline axis;
• an upper portion including a pair of upright arms defining an open channel configured to receive the elongate rod and an upper portion of the central bore communicating with the open channel and configured to receive the closure top;
• and
• a lower portion including a downwardly extending collet structure having an inner surface defining a lower portion of the central bore communicating with a bottom surface of the receiving member through a collet opening, the collet structure configured to expandingly receive the head of the shank upon the head being uploaded through the collet opening;
• a pressure insert configured for positioning into the central bore prior to uploading the head of the shank into the collet structure, the pressure insert having an upward-facing surface configured to receive the elongate rod and an inner lower surface configured to engage the head of the shank;
• and
• an outer ring configured for positioning on the receiving member at least partially above the collet structure prior to uploading the head of the shank into the collet structure, the outer ring being downwardly slidably engageable with an outer surface of the collet structure so as to inhibit the collet structure from expanding,
• wherein after the head of the shank has been uploaded through the collet opening and captured within the lower portion of the central bore, the pressure insert is configured for downward compression against the head of the shank by force from the closure top so as to lock the position of the shank with respect to the receiving member, and
• wherein the upward-facing surface of the pressure insert is above a top surface of the outer ring when the pivotal bone anchor assembly is in a locked configuration.