Pediatric Spine Trauma: A Brief Review




EPIDEMIOLOGY

The epidemiology of spinal column trauma in children is highly dependent upon the patient's age; age, in turn, is closely related to the frequency of injury, causes of injury, vertebral level of injury, and the specific pattern of injury. Comprehensive data for children less than 18 yr of age gathered from the KIDS Inpatient Database over a 15-yr period have recently been published1 and are discussed below.

Frequency of Injury

Over the last 20 yr, there has been a decreasing trend in annual incidences of both spinal column and spinal cord injury among pediatric patients in the United States.2 The incidence of spinal column injury in children and adolescents below the age of 18 is approximately 93 per million per year, whereas the incidences of spinal cord injury in the same population is approximately 14 per million per year.1 Adolescents (defined as between 15 and 17 yr of age) have a 6 times greater incidence of spinal cord injury than children (defined as ages 0-14 yr) at 45 per million annually.1 In North America, there are 2 incidence peaks for spinal cord injury, one in the summer from June to September and the other during winter from the end of December through January.3

Causes of Injury

Motor vehicle accidents (MVAs) account for 50% of spinal column injuries in adolescents and 32% in children, making them the most common cause of spinal column injury in both populations.1 Falls accounted for 10% of spinal column injuries in adolescents and 18.3% in children. Although penetrating injuries were more prominent in adolescents at 3.4%, children were more likely to suffer spinal column injury because of pedestrian injuries (6.8%) and nonaccidental trauma (1.7%). Although MVAs account for the greatest number of spinal column injuries in pediatric patients, penetrating injuries and sports injuries account for the greatest frequency of spinal cord injuries. Penetrating injuries account for between 55% and 60% and sports injuries between 25% and 30% of spinal cord injuries in both children and adolescents.1

Vertebral Level of Injury

Overall, lumbosacral injuries are more common than cervical injuries in pediatric patients. The incidence of hospitalization for lumbosacral spinal injury is 36.0% in children and 43.1% in adolescents, whereas for cervical spinal injuries, the numbers are 29.3% in children and 22.3% in adolescents. Although lumbosacral injuries are more common in pediatric patients, it is injuries of the upper and lower cervical spine that more frequently result in spinal cord injury in the same population. Cervical injuries are also more likely to cause spinal cord injury in pediatric patients when compared to adult patients. Although cervical injuries account for 30% to 40% of spine trauma in adults, they account for 80% of spine trauma in pediatric patients.4 The anatomy of a pediatric spine under development makes injury to the upper cervical spine more likely.1,5 As a general rule, children are more likely to have an upper cervical injury the younger they are. In children, the incidences of upper cervical spine injury is 21.0% compared to lower cervical spine injury at 8.3%. In adolescents, however, that disparity essentially disappears, as the incidence of upper and lower cervical injury is similar at 10.9% and 11.4%, respectively.1

Patterns of Injury

There are generally 4 patterns of injury seen in pediatric patients with spinal column trauma: (1) fracture with subluxation, (2) fracture without subluxation, (3) subluxation without fracture (purely ligamentous injury), and (4) spinal cord injury without computed tomograhy (CT) evidence of trauma (SCIWOCTET).6 Younger children (0-9 yr) are more likely to suffer purely ligamentous injury or SCIWOCTET because of ligamentous laxity, incomplete ossification of the vertebrae, and underdeveloped neck muscles.7 It is more common for older children and adolescents (10-17 yr) to have fractures with or without subluxation. For instance, in cases of pediatric cervical spine injury, children (0-10 yr) suffer a 7.2% incidence of fracture in comparison to adolescents (11-18 yr), who suffer a 55.4% incidence of fracture.4 Injuries to the upper cervical spine, specifically from the occiput to the C2-C3 level, are associated with a greater risk of neurological damage and also have a 25% to 50% prevalence of associated head injuries. Because pediatric anatomy predisposes children to increased upper cervical spine injury, younger children suffer a significantly higher incidence of neurological injury than adolescents.5

BIOMECHANICS

General

The developing pediatric spine contains several important anatomical and physiological differences from the mature adult spine. Those differences include incomplete ossification of the vertebrae and synchondrosis, absence of lordotic curvature, anterior wedging of vertebral bodies, pseudosubluxation, and pseudospread of the atlas on the axis.8 The net effect of these differences is that the pediatric spine is much more flexible to external forces but, because of less protection, is far more susceptible to damage to the underlying spinal cord. The developing pediatric spine, particularly the cervical spine, reaches adult biomechanical maturity between the ages of 8 and 10 yr.9 This is one of the primary reasons, as mentioned previously, that children younger than 8 to 10 yr old suffer upper cervical spinal cord injuries, whereas adolescents experience lower cervical injuries more frequently.1,8

Based on this understanding, several general biomechanical principles have developed and persisted over the years. First, compared with the adult spine, the pediatric spinal column is less likely to suffer fractures and ligamentous injuries because of its increased flexibility from its elastic ligaments. However, it is more likely to sustain spinal cord injury with purely ligamentous injury1 second, because the pediatric spine is more flexible, it experiences more intervertebral displacement from external forces. That increased displacement results in less protection for the spinal cord, allowing for spinal cord injuries without associated fracture or subluxation. Third, the upper cervical spine is the most unstable region of the pediatric spine. Accordingly, younger children experience more severe spinal cord injuries when the upper cervical spine is injured. Lastly, lower cervical injuries should be more common in older children and adolescents because, after 8 to 10 yr old, the cervical spine more closely resembles the injury pattern in adults.8

Although data regarding the biomechanics of the pediatric spine are extremely limited, data regarding the anatomical growth of the pediatric cervical spine during development have recently been published.10 Normal vertical growth is seen until the age of 18 in boys and 14 in girls, with the subaxial spine responsible for 75% of growth and the craniovertebral region responsible for 25%. Although vertical growth proceeds throughout childhood and adolescence, the bulk of spinal canal diameter growth is complete by age 4.10

Craniovertebral Junction and Subaxial Spine

The biomechanical unit of the craniovertebral junction (CVJ) is the occipitoatlantoaxial (O-C2) complex. The CVJ is the most susceptible zone of the pediatric spine to injury and potential instability for several reasons: (1) predisposition to increased motion in children vs adults, (2) less-developed muscles and ligaments, and (3) an unfused dentocentral synchondrosis prior to 8 yr of age. With regard to the subaxial spine, the upper cervical region is predisposed to injury from flexion forces as a result of hypermobility because of ligamentous laxity, particularly between C2 and C3.

Thoracolumbar Spine

As with the pediatric cervical spine, the pediatric thoracolumbar spine is dynamic with increased ligamentous laxity and incomplete ossification. Children's facet joints are more horizontally oriented, leading to less stability with greater mobility. As the spine matures to a more adult-like osseoligamentous configuration between the ages of 9 and 16, increased likelihood of fracture and dislocations vs ligamentous injury mirror that in the cervical spine.11,12

DIAGNOSIS AND MANAGEMENT

Initial Evaluation

Initial evaluation and management for any pediatric patient in whom spinal column trauma is suspected should proceed in a standardized fashion. Further diagnostic imaging and management decisions can then be segregated depending on the suspected general level of injury (cervical vs thoracolumbar). At presentation, general trauma guidelines should be followed with primary attention to airway, breathing, and circulation along with the maintenance of adequate systemic perfusion and oxygenation.

During this initial care, immobilization of the spine is critical to prevent further injury, particularly in an unstable or unresponsive patient. Although older children can be immobilized in the standard fashion with cervical collars and backboards, immobilization of younger children is more nuanced. Young children and infants have larger heads in proportion to their torsos, resulting in cervical flexion when placed supine on a flat surface.13-15 As such, specialized boards with head recesses should be used when available or bolsters should be placed to elevate their torsos relative to their head in order to keep the neck in neutral position. Appropriate sizing of cervical collars in infants can also be challenging, particularly in the acute setting, and can lead to inadvertent exacerbation of injuries with transport; secure taping of the head and torso to backboards can mitigate this risk.

Although there is abundant literature regarding specific modalities of imaging in suspected cervical spine trauma, little evidence exists regarding recommended imaging for suspected thoracolumbar injury.15 Historically, the mechanism of injury has guided decision-making regarding imaging in trauma patients. However, more recent recommendations from a Delphi study centered around pediatric cervical spine clearance argue against its dominant role in triggering acquisition of imaging.16 Nevertheless, specific mechanisms of injury are significantly associated with underlying spinal column injuries and should prompt strong consideration of screening imaging, including diving injuries, “clothes-line” injuries, high-risk motor vehicle injuries, seat-belt-type injuries, falls, and suspected non-accidental trauma. The presence of specific neurologic deficits or localized axial neck or back pain should further guide imaging choices. When a spinal column injury is identified at any level, screening of the remainder of the spinal column is indicated given reported incidences up to 32% of contiguous injuries and 6% noncontiguous injuries.17,18

Cervical Spine

Diagnosis

The identification of cervical spine injuries is of paramount importance in all trauma patients given the potential catastrophic outcomes from missed unstable pathology. Given the increased risk of radiation in the pediatric population compared to adults, minimization of unnecessary imaging must be incorporated into clinical decision making.19 Clinical algorithms for cervical spine clearance have been shown to appropriately diagnose occult injuries and decrease both exposure to ionizing radiation and time required for clearance.20,21 It is, therefore, surprising that a recent study found that only 46% of surveyed level 1 pediatric trauma centers in North America had written pediatric cervical spine clearance protocols.22

The most common method used to clear the pediatric cervical spine is The National Emergency X-Radiography Utilization Study (NEXUS), which has been validated in children less than 18 in a large study by Viccellio and colleagues.23 This study defined 5 NEXUS criteria: the presence of neurologic deficits, midline spinal tenderness, altered level of consciousness, intoxication, and distracting injuries. No children defined as low risk (meeting no NEXUS criteria) were ultimately diagnosed with cervical spine injuries, whereas 1% of children in the high-risk group (meeting at least 1 NEXUS criteria) were ultimately found to have cervical injuries.23

Recommendations for imaging after spinal trauma have been made by the AANS/CNS Joint Guidelines Committee.15 Briefly, level 1 evidence only exists for the use of CT to determine the condyle-C1 interval in suspected atlanto-occipital dislocation. Level 2 evidence recommends against imaging in children > 3 yr of age who are alert, have no neurologic deficits, have no midline tenderness, have no distracting injuries, are not intoxicated, and have no unexplained hypotension along with children <3 yr old who meet the above criteria and have GCS >13 with mechanisms other than MVA, fall from height greater than 10 feet and nonaccidental trauma. Cervical spine radiographs or CT scan are the recommended imaging modalities for children not meeting these criteria. More recently, a consensus statement by the Pediatric Cervical Spine Clearance Working Group utilized the Delphi method of consensus building among multidisciplinary experts to create a new algorithm to guide pediatric cervical spine clearance and imaging decisions.16 As outlined in Figure 1, clearance and imaging are divided based on presenting GCS with AP and lateral radiographs as the initial imaging of choice for patients with GCS of 14 to 15 and any of the outlined history or physical exam findings. In patients with GCS of 9 to 13 whose mental statuses are unlikely to improve and all patients with GCS 8 or below, a CT scan is recommended.

Figure 1.

Management

Most children presenting with cervical spine trauma do not ultimately require surgical intervention and may be managed with external orthoses and serial imaging. Although a discussion of the management of all cervical spine injuries is beyond the scope of this report, there are several types of injuries that can typically be managed with external bracing in the absence of neurologic findings including (1) Jefferson(C1) fractures with minimal ligamentous disruption and an intact transverse ligament, (2) acute and subacute atlantoaxial rotary subluxation/fixation, (3) minimally displaced or angulated odontoid fractures and hangman (C2 pedicle) fractures, and (4) minor ligamentous injuries without instability.24 A halo ring and vest provide the best immobilization of the CVJ and upper cervical spine while also allowing for traction application when indicated. Minerva braces may be used in children who cannot tolerate halo application but may not be tolerated in some children because of the need for a rigid piece under the chin that may limit ability to eat and speak.25 Rigid cervical collars offer the least stability but are generally well tolerated.

In the setting of progressive neurologic deficits or gross instability, surgical intervention is indicated. Common types of cervical spine traumatic injuries that are likely to require surgical intervention include (1) fracture dislocation, (2) burst fracture (Figure 2), (3) compression fractures with deformity (Figure 3), and (4) atlanto-occipital dislocation. In order to keep the neck in neutral position, awake fiberoptic intubation is preferred with fiberoptic nasal intubation as an alternative. Intraoperative monitoring with prepositioning somatosensory and motor evoked potentials should be employed, and alignment should be maintained with a rigid cervical collar during positioning and confirmed with lateral fluoroscopy following positioning.


Figure 2.


Figure 3.


Craniovertebral Junction

In the presence of atlanto-occipital instability, occipitocervical fusion is indicated with rigid instrumentation preferred over wiring techniques alone.26 The common constructs that anchor occipitocervical fusions such as C1-2 transarticular screws, C1 lateral mass, and C2 pars, and pedicle screws provide the basis for the management of atlantoaxial fractures and instability.

In children, preoperative planning is essential to determine the feasibility of screw placement given the smaller size and frequency of congenital abnormalities. Prior reports have indicated that rigid instrumentation can be used safely in children as young at 1.5 to 2 yr of age using the smallest commercially available screws. Table summarizes the youngest age and screw diameter used in the literature for individual cervical screw types. Generally, C1-2 transarticular screws provides excellent rotational and translational stability across the C1-2 joint with superior fusion rates.27-30 However, vertebral artery anatomy may prevent transarticular screw placement in 11% to 20% of cases unilaterally and 4% to 5% of cases bilaterally.30,31 C1 lateral mass screws coupled with C2 fixation are another excellent option for fixation. The key measurement in placement of C1 lateral mass screws in children is whether the lateral mass width allows for a 3.5-mm-diameter screw. In O-C2 constructs, equivalent fusion rates have been found with or without the placement of C1 instrumentation and they are thus often left out.32 C2 fixation may be achieved using pars, translaminar or pedicle screw placement depending on anatomy and the ability of each approach to accommodate a 3.5-mm-diameter, 8-10-mm-length screw. C2 pedicle screws likely provide the greatest mechanical strength, but this has not been assessed in biomechanical studies in children; furthermore, children under the age of 10 may not have pedicle widths large enough to accommodate screw placement.33 Instrumentation of the occiput may be performed, preferably using occipital plates and 6 to 10-mm midline occipital keel screws, but occipital condylar screw placement may be performed as an alternative.34


Rigid fixation with structural autograft using either rib or iliac crest have demonstrated fusion rates of up to 100% in multicenter studies.32,35 A recent systematic review of the literature found overall fusion rates of 93% with 94% fusion using autograft and 80% fusion with allograft.36 However, more recent multicenter studies as well as data utilizing insurance database queries have suggested nearly equivalent fusion rates using autograft and allograft with approximately 10% fusion failure regardless of graft type.37-39 Given the morbidity associated with harvesting autograft along with more modern screw rod constructs that better facilitate fusion, allograft may serve as a reasonable alternative.

Subaxial

Management of subaxial cervical spine injuries in children is similar to in adults with the key determination being the stability of the injury. Stable injuries without neurologic symptoms may be managed with rigid external fixation. Closed reduction may be challenging in children because of noncooperation and low body weight for countertraction and thus are usually performed in the operating room with lateral fluoroscopy to prevent overdistraction.14

The operative approach to subaxial injuries in children depends on the site of injury and compression, patient age, size of boney elements, and surgeon experience. In most children over 5 yr of age with primarily anterior pathology including disc rupture, burst fractures, or irreducible kyphotic deformities, an anterior approach with graft and plating is generally preferred. In younger children, a single screw and anterior plate system may be employed.40 In exceptional cases of very young children, if these traditional spinal instrumentation systems are still too large, instrumentation from the oral maxillofacial or orthopedic hand plating systems can be used, typically with additional support from posterior instrumentation or external immobilization (Figure 2).40 In cases of primarily posterior ligamentous injury, irreducible facet subluxation, nerve root compression or epidural hematoma, a posterior approach is generally preferred. Lateral mass screw placement is feasible in most children over the age of 4 based on CT morphometric studies.41 The advent of intraoperative navigation has enabled the safe placement of subaxial cervical pedicle screws providing increased mechanical strength; from our own experience and very limited published data, neurovascular injuries and other complications are rare.