An anchor assembly for use with a fixation system for stabilizing one or more spinal bone segments by means of an elongated stabilizer includes an an chor base that receives a fastener and includes s a first coupling feature i ncluding guide slots and a recessed channel for receiving the elongated stab ilizer. The anchor assembly further includes a cap that has a second couplin g feature that is complementary to the first coupling feature and includes s tructures that are laterally received in the base guide slots for mating the cap to the base, as well as a stop element that in combination with the fir st coupling feature limits the lateral movement of the cap in the guide slot s. The cap includes a retaining element that is driven into engagement with the elongated stabilizer so as to lock and retain the elongated stabilizer i n place within the anchor assembly.
