A bone interface anchor for use with an elongated stabilization member, the anchor having: a receptor having a retaining device for receiving the elongated stabilization member a compression assembly for securing the elongated stabilization member within the receptor bone fixation screws which secure the anchors relative to bone segments of the human spine,the receptor having a surface forming a mating cooperation with the screw such that the receptor can be variably positioned relative to the screw, a lock member to fix the screw relative to the receptor, and the retaining device having a retaining member between the elongated stabilization member and the interior of the receptor.
