Introduction Fixes skull relative to the torso provides the most rigid form of external immobilization for the cervical spine ideal for upper cervical spine injury Allows intercalated paradoxical motion in the subaxial cervical spine not ideal for lower cervical spine injuries as lateral bending is the least controlled motion "snaking phenomenon" recumbent lateral radiograph shows focal kyphosis in the midcervical spine yet, upright lateral radiograph shows maintained lordosis in the midcervical spine Indications Adult definitive treatment of cervical spine trauma including occipital condyle fracture occipitocervical dislocation stable type II atlas fracture (Jefferson fracture) type II odontoid fractures in young patients type II and IIA Hangman’s fractures adjunctive postoperative stabilization following cervical spine surgery Pediatric definitive treatment for atlantooccipital dissociation Jefferson fractures (C1 burst fracture) atlas fractures unstable odontoid fractures persistent atlantoaxial rotatory subluxation C1-2 dissociations subaxial cervical spine trauma preoperative reduction in patients with spinal deformity Contraindications Absolute cranial fractures infection severe soft-tissue injury especially near proposed pin sites Relative polytrauma severe chest trauma barrel-shaped chest obesity advanced age recent evidence demonstrates an unacceptably high mortality rate in patients >79 y/o (21%) Imaging CT scan prior to halo application indications clinical suspicion for cranial fracture children <10 y/o to determine thickness of bone Adult Technique Adults torque tighten to 8 inch-pounds (in-lb) of torque location total of 4 pins 2 anterior pins safe zone is a 1 cm region just above the lateral 1/3 of the orbit (eyebrow) at or below the equator of the skull anterior and medial to temporalis fossa/temporalis muscle lateral to supraorbital nerve 2 posterior pins placed on the opposite side of the ring from anterior pins followup care can have the patient return on day 2 to tighten pins again proper pin and halo care can minimize the chance of infection Pediatric Technique Pediatrics torque best construct involves more pins with less torque total of 6-8 pins lower torque (2-4 in-lb or "finger-tight") pin locations place anterior pins lateral enough to avoid injury to the frontal sinus, supratrochlear nerve, and supraorbital nerve place pins anterior enough to avoid the temporalis muscle place posterior pins opposite from anterior pins brace/vest custom fitted vest for children >2 y/o Minerva cast for children <2 y/o CT scans may help in pin placement can help avoid cranial sutures can help avoid thin regions of the skull help limit risk of complications Complications Higher complication rates in children (70%) than adults (35%) Pin loosening (36%) can be treated with retightening if pin continues to loosen, should be treated with pin exchange Infection (20%) especially occurs with a posterior pin in the temporalis fossa pins hidden in hairline bone is thin temporalis muscle moves with chewing can be treated with oral antibiotics if the pin is not loose if there is a pin infection and the pin is loose, then the pin should be removed Discomfort (18%) treated by loosening the skin around a pin Dural puncture (1%) Abducens nerve (cranial nerve VI) palsy epidemiology most commonly injured cranial nerve with halo placement pathophysiology thought to be a traction injury to cranial nerve VI (abducens nerve), which innervates lateral rectus muscles symptoms diplopia physical exam loss of lateral gaze on affected side treatment observation, as most cases resolve spontaneously Supraorbital nerve palsy injured by medially placed anterior pins Supratrochlear nerve palsy injured by medially placed anterior pins Medical complications pneumonia ARDS arrhythmia