The halo vest immobilizer (HVI) is a device that restrains the cranium to the torso, for both adult and pediatric patients. This device provides the most rigid form of external immobilization for the upper cervical spine (occipitocervical and atlantoaxial junction). When compared to conventional cervical orthoses (CO), it is the best choice for immobilizing the upper cervical spine since it can restrict atlantoaxial joint flexion-extension by 75% versus only 45%, respectively. When applied, there is intercalated paradoxical motion (least controlled being lateral bending) within the sub-axial cervical spine (at/below C3), and therefore conventional cervical orthoses are more effective in immobilizing this region. Originally developed, in 1959 by Perry and Nickel, to provide cervical immobilization for occipitocervical fusion in poliomyelitis patients, this device application protocol and vest design has since evolved allowing for a multitude of uses including the definite treatment of upper cervical spine trauma (most common), preoperative reduction of spinal deformities, and postoperative adjuvant stabilization. Examples for definitive treatment are occipital condyle fractures, occipitocervical dislocation, C1 (most Common), and C2 fractures, with an anticipated average healing time of 3 to 4 months. When used as definitive treatment, the success rate has been reported to be around 85%. However, this is directly affected by proper indication, application, and management of the device. The HVI does come with risks, which has made providers reluctant to use as definitive treatment, especially in the elderly. In the pediatric population, this device can be used for cervical spine trauma (definitive or conjunction with surgical management), severe scoliosis, and arthrodesis. HVI is also safe for toddlers (less than 4 years old), however, ambulation should be restricted within this age group. Pediatric and toddler populations have reduced skull thickness. Therefore there are differences in HVI application, which include using a higher number of pins (8-12) onto the cranium, with a lower insertion torque force (1 to 5 inch-lb). The HVI has been shown to have successful outcomes for managing some cervical spine injuries. However, there are strict indications for its use in the pediatric and adult population, particularly the elderly.
Anatomy and Physiology
Providers must understand the anatomy of the frontal cranium as it is essential for guiding anterior pin placement. The described “safe zone” is an area located 1cm superior, over the lateral two-thirds of orbit rim (eyebrow) and just below the level of the largest cranial circumference (found 0.5 to 1cm above the top of the ears). The most medial portion of the safe zone is approximately 4.5 cm from the midline in the sagittal plane, and pin placement medial to this should be avoided. Medial to this region lies the supraorbital and supratrochlear nerves (from lateral to medial), both being terminal branches of the ophthalmic division of the trigeminal nerve, which provide sensation to the frontoparietal scalp and portions of the nasal bridge. The frontal sinus is medial to the safe zone as well and should be avoided since it’s thinner and more susceptible to pin perforation. Important anatomy lateral to this “safe zone” includes the temporal bone (thinner), temporalis muscle, and the zygomaticotemporal nerve. If anterior pins are placed too lateral, perforation, irritation with mandibular motion, and numbness or paresthesias along the temporal region can occur, respectively.
Indications for definite use in adults include:
- Occipital condyle fracture
- Occipitocervical dislocation
- Stable type II atlas fracture (C1)
- Type II odontoid fractures in young patients (C2)
- Type II and IIA hangman fractures (C2)
Indications for temporary use in adults:
- Adjunctive immobilization postoperatively from cervical spine surgery
Indications for definitive use in pediatric patients include:
- Atlantooccipital dissociation
- Burst fracture of C1 (Jefferson fracture)
- Atlas fractures
- Unstable odontoid fractures
- Persistent atlantoaxial rotatory subluxation
- C1-C2 dissociations
- Subaxial cervical spine trauma
- Idiopathic or congenital scoliosis
- Preoperative reduction in patients with spinal deformity
- Cranial fractures and or severe bone deficiency
- Patients who require a craniotomy
- Severe soft-tissue disruption over and or near proposed pin sites
- Penetrating chest injury
- Pulmonary contusion
- Barrel-shaped chest
- Advanced Age (more than 65 years old, increased risk for complications and death)
Required equipment for this procedure include:
- Anesthetic agent: lidocaine hydrochloride 1% solution, 10 mL to 20 mL.
- 25 gauge needle
- Syringe, 10 to 20 mL
- Sterile gloves
- Povidone-iodine solution or another form of antiseptic skin preparation solution
- Crash cart (manual resuscitator, endotracheal tube) in case airway management is needed or any cardiopulmonary complications occur.
- Sterile halo ring (size pre-selected, measured from the largest circumference of the head)
- Sterile halo pins (total of five, one serving as a spare)
- Halo pin locknuts (total of five, one serving as a spare)
- Halo torque screwdriver or breakaway wrenches (if wrenches are used, will need 4 of them)
- Ratchet wrenches
- Halo vest (size pre-selected, from the circumference of the chest at the xiphoid process)
- Halo upright post (4) and connecting rods (2)
Ideally, a minimum of two person teams is required. This includes the physician and an assistant (nurse, physician assistant, or resident).
The patient (or next of kin/health care proxy if the patient is obtunded) should be educated about the procedure along with the risks/benefits that are involved. Once consent is obtained, the proper equipment and personnel should be present at the bedside. Patients should be moved into a controlled environment; procedure room or operating room. Sedation, either partial or full, may be used. General anesthesia is not required, however, if used, an anesthesiologist must be present, and preferred to be done so in an operating room.
For adults, the procedure is performed in the following steps:
- The patient is placed supine on a bed/gurney, and the head is placed 8-10 inches beyond the edge supported by a head positioner (usually included with halo application kit).
- The largest circumference of the cranium is measured in the coronal plane, which provides the appropriate halo ring size. This circumference is usually located 0.5 to 1 cm above the ears. Once measured, hold the appropriate sterilized ring over the head to confirm the measurement is correct. This is performed with sterile technique, providers must be wearing sterile gloves.
- Halo vest size is determined by measuring the circumference of the chest at the xiphoid process.
- Identify the pin-site locations while holding the ring in place. The ring should be placed one-half centimeters above the eyebrows. Make sure the ring is centered, with equal space from ring to cranium circumferentially.
- The posterior pins should be placed directly opposite to anterior pins bilaterally (from the safe zone) and prepare the skin for all four pin sites with a povidone-iodine solution or other antiseptic solutions with sterile technique.
- The skin at each pin site should then be anesthetized with 1% lidocaine hydrochloride, using a 22 gauge needle with a 10 or 20 mL syringe depending on the amount of anesthetic required.
- Once ring position is satisfactory, the positioning pins (already on the halo ring) are then advanced by hand to hold the halo ring temporarily in place.
- Sterile pins are then advanced through the circles in the halo ring and onto the skin at all four points. The patient is asked to close his/her eyes tightly before the anterior pins are advanced through the skin and onto the cranium. This will help prevent patients from having permanent open eyes and not being able to close them from anterior pins causing skin tension.
- Simultaneously, tighten one anterior pin along with the diagonal opposite posterior pin, by hand, making sure that the pins are being advanced perpendicular to the cranium. Once all four pins are finger tight and at ninety-degree angles to the cranium, use the preset torque screwdriver that is provided with the Halo application set/kit. Tighten pins with the torque screwdriver at 2 in-lb increments, making sure to proceed in a diagonal alternating fashion onto all 4 pins. The torque screwdriver has the in-lb measurement displayed so that the exact measurement in increments can be recorded. All 4 pins must be fixed with 8 in-lb of torque.
- Once this is reached, apply the locknuts to each pin. At this time, the temporary positioning pins can be removed.
- The vest application starts with the posterior portion fitted first (divided into an anterior and a posterior portion connected by straps). To do so, the provider holds/stabilizes the head (maintaining reduction) while the assistant applies the posterior vest underneath.
- The posterior vest, once applied and centered, is then attached to the fixed halo ring with uprights bilaterally. For maximum stability, the upright bars must be parallel to each other (anterior crossbar being parallel to the posterior).
- Apply the anterior vest portion, and connect it to the posterior portion with the appropriate straps. Next, attach the anterior uprights to the halo ring.
- Connect the anterior and posterior uprights with crossbars bilaterally. Make sure all uprights are at ninety-degree angles to the crossbars for added equal stability as required.
- Adjust the flexion and extension of the ring to the uprights as required.
- Recheck all screws, pins, nuts, and make sure everything is tightened appropriately.
- Tape all wrenches and necessary tools to the anterior vest shell (allows for accessibility in case of an emergency for vest removal is needed or for bolt/pin tightening as needed by provider physician).
- Pin sites must be uncovered to allow for cleaning with hydrogen peroxide or betadine solution every day or every other day. It is recommended to use a cotton swab to mobilize the surrounding skin around each pin site. This will help minimize the risk of pin site infection.
- Retorque each halo pin again at 24 hours after application, to 8 in-lb. Recheck halo fixator 2 days after original application followed by every 3 to 4 weeks thereafter to make sure pin sites are at appropriate tightness.
For pediatric patients, certain Technique modifications include:
- The torque applied to each pin is lower, with insertional torque ranging from 1-5in-lb of pressure (reduce the risk for pin perforation through cranium).
- The Number of pins used ranges from 8 to 12, allowing for increased surface area, thus reducing the risk of pin perforation.
- Pin Location is still at the safe zone anteriorly. Place posterior pines opposite from anterior pins.
- Brace/vest usually requires to be custom fitted for children more than 2 years old. For toddlers, less than 2 years of age, recommended using a Minerva cast.
- Computed tomography (CT) scans may help with pin placement by avoiding cranial sutures, and thin regions of the skull. However, CT scans provide a lot of radiation exposure to the pediatric patient, where the risk may outweigh the benefit.
Providers have a multitude of treatment options ranging for nonoperative external immobilization, to operative stabilization for cervical spine injuries and deformities in both adults and children. In recent history, the halo vest immobilizer has become a less utilized form of external immobilization due to its known common complications, advancement in cervical surgical fixation/fusion, and the understanding to accept more pseudoarthrosis that occurs from elderly immobilization with CO. The HVI, however, can still provide the most rigid form of external immobilization, therefore when indicated (patients who may not tolerate surgery or younger patients), it can still serve as a successful treatment option.
Treatment success with HVI is directly proportional to following proper indications, application, and, most importantly, maintenance and management protocols of the device, which should be carried throughout the whole immobilization period (average of 12 weeks). This includes re-tightening of the pins 24 to 48 hours after original placement, with follow up every 3 to 4 weeks thereafter. Pin site care must be performed daily or every other day to help limit pin site infection. Radiographs are taken at provider follow up appointments, to confirm the reduction remains acceptable.
Additionally, further imaging such as CT scans may help with pre-procedure pin placement planning, as anatomic variation does exist in pediatric patients. This can help avoid pin placement at cranial sutures, thin cranium regions, and overall help limit the risk of complications.
Once a provider becomes familiar with the important anatomy, and technical steps for safe pin placement and proper halo application, this procedure serves as an essential tool for a cervical spine provider's practice. Despite complications that can commonly occur (often minor), successful treatment with the HVI has been reported to be as high as 85%. Therefore the HVI may serve as a reasonable option, when indicated, for certain cervical spine injuries.
Enhancing Healthcare Team Outcomes
Application of the halo vest immobilizer (HVI) is a team guided procedure, requiring at least 3 individuals, including a clinician, nursing staff, and/or physician assistants/residents. Before the procedure is initiated, the clinician must designate each assistant's roles, thus eliminating any confusion as to what is expected from each other.
During HVI applications, It is critical that all team members understand basic principles of sterile technique and maintaining a sterile field, as it is required from the part of this procedure (halo ring and pin placement). Before the procedure, patient information regarding age and past medical history must be obtained, as it has been reported that patients with advanced age (older than 65 years) and cardiopulmonary complications are at higher risk for complications with HVI. Additionally, all required imaging of the cervical spine that is needed for an accurate diagnosis must be performed before the HVI application. This will help eliminate any unnecessary application of the HVI for injuries where it isn't indicated. A crash cart must be at the bedside as well, in case airway access is needed at any time prior, during, or after the procedure.
An interprofessional team that provides an integrated approach in managing the maintenance of HVI application is important in first recognizing complications early, as well as preventing them from producing morbidity and mortality. In a recent prospective cohort study evaluating 239 patients who were treated with HVI following cervical spine trauma, the rates of mortality and pneumonia complications were found to be relatively low. Elderly populations (older than 65years) did not represent an increased risk of pneumonia or death, however, there were a substantial number of minor complications between all age groups. Minor complications comprised a total of 121 of the 239 patients. The most common minor complications being the loss of cervical alignment, which occurred in 164 trauma patients, and pin site infections, which occurred in 12% of the patient. However, as shown by this studies' relatively low mortality and pneumonia rate, it confirmed that responsiveness and awareness of these such minor complications can help prevent the further development of morbidities and reduce mortality, especially when a team-based approach is applied to these patients. [Level 3]
To help prevent the more common minor complications, such as pneumonia and pin site infections, incentive spirometer and Pin site care must be performed daily, respectively. This can be ordered by the provider and performed by trained nursing staff. If such complications are suspected, medical professionals such as pulmonologists and infectious disease physicians must be consulted to prevent further morbidity and progression. To prevent pin loosening, spine providers and or residents must check the torque of all pins 24 hours after the initial application, followed by every three weeks thereafter.