Cervical spine surgery performed for correction of prior surgery.Headache and dizziness returned.Ct found that a screw had migrated and transected the vertebral artery resulting in bleeding.Patient also had suffered a stroke.Transferred to neuro icu.Third surgery performed to replace screw.Dizziness persists.Surgeon reports inaccuracy of equipment used on cervical cases-stealth navigation system resulted in screw placement being off.Fda safety report id # (b)(4).