1. A spinal fixation system, comprising: a bone anchor having a bone-engaging portion and a spinal fixation element receiving portion with opposed arms configured to receive a spinal fixation element therebetween; a connecting member having first and second ends, the first end having an elongate opening extending therethrough; a washer configured to slide along the first end of the connecting member to adjust a distance between the bone anchor and the second end of the connecting member; and a locking mechanism configured to simultaneously lock the washer in a fixed position along the first end of the connecting member, and to lock the first end of the connecting member to the spinal fixation element receiving portion of the bone anchor.
8. The system of claim 1 , further comprising a coupling member mated to the second end of the connecting member, the coupling member having a spinal fixation element receiving recess formed therein for coupling to a spinal fixation element without anchoring to bone.