An anchor assembly for use in spinal fixation to interconnect a longitudinal spinal rod with a patient's vertebra. The anchor assembly preferably includes a bone anchor, a body with a rod-receiving channel, an insert member (preferably a bushing), and a locking cap. The anchor assembly enables in-situ assembly where the bone anchor may be secured to the patient's vertebra prior to being received within the body of the bone anchor assembly. Accordingly, the anchor assembly enables a surgeon to implant the bone anchor without the body to maximize visibility and access around the anchoring site. Once the bone anchor has been secured to the patient's vertebra, the body may be snapped onto the bone anchor and a spinal rod may be inserted into the rod-receiving channel.