A pivotal bone anchor assembly includes a shank having a shank head and an anchor portion, and a receiving member having an upper portion defining an open channel for receiving an elongate rod and a lower portion with a downwardly extending collet structure defining a lower portion of a central bore for receiving the shank head upon uploading through a lower collet opening. The assembly also includes a pressure insert positionable into the central bore prior to uploading the shank head, and an outer ring slidably engageable with an outer surface of the collet structure to inhibit the collet structure from expanding. After the shank head has been uploaded and captured within the central bore, the pressure insert is downwardly compressed against the shank head by the elongate rod so as to lock the position of the shank with respect to the receiving member.