Management of Injuries of the Cervical Spine and Spinal Cord

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Chapter 174 Management of Injuries of the Cervical Spine and Spinal Cord

The cervical spine is the most frequently injured portion of the spinal column, with the most common causes being automobile accidents, violent trauma, and sports-related injuries. An understanding of radiographic features allows a more accurate determination of which injuries are unstable and may require external orthoses, cervical traction, surgical fixation, or emergent decompression of the spinal cord.

Upper Cervical Spine

The upper cervical spine consists of the occipital condyles: atlas (C1) and axis (C2). At the craniocervical junction, the two main injuries include occipitocervical dislocations and occipital condyle fractures. These injuries are often the result of high-energy trauma in children or young adults and typically result in severe neurological deficit or even death at the scene. In elderly patients, the majority of spinal column injuries occur at the C1-C2 level following relatively minor trauma, and they are associated with a much lower rate of neurological compromise.

Occipitocervical Dislocations

Atlanto-occipital dislocation (AOD) is the most unstable and dangerous injury of the cervical spine. It results from ligamentous disruption between the occiput and the cervical spine. Severe neurological morbidity and mortality are due to the combination of extreme instability and the possibility of a high cervical cord injury that can lead to quadriparesis and diaphragm paralysis. Fewer than 20% of patients with this devastating injury have a normal neurological examination. In these patients, neurological deficits occur as a result of injuries to the caudal cranial nerves, the brain stem, the upper cervical cord, and the nerve roots. Vertebral artery injuries resulting in brain stem stroke may also occur.

A number of radiographic techniques are used to diagnose AOD. The Powers ratio provides a mathematical relationship between the basion (B), the opisthion (O), the anterior arch of C1 (A), and the posterior arch of C1 (C).¹ To apply this ratio, two lines are drawn: one from the basion to the posterior arch of C1 and another from the opisthion to the anterior arch of C1. The ratio of the lengths of these two lines defines Powers ratio, with a value of B×C/O×A >1 raising concern for atlanto-occipital dislocation. This ratio may be unreliable C1 fracture or posterior subluxation cases. The method of Harris et al.² uses a combination of basion-dental interval to detect longitudinal displacement (normal, less than 12 mm) and basion-axial interval to detect anterior and posterior displacement (normal, 0 to 12 mm). Imaging studies should involve reconstructed computed tomographic scans and MRI studies, with the latter invariably showing ligamentous injury. Because of the extreme instability of occipitocervical dislocations, flexion-extension x-rays are absolutely contraindicated.

A classification scheme developed by Traynelis et al ³ involves three types of injury. Type I injuries include anterior displacement of the skull in relation to the cervical spine, type II injuries involve longitudinal displacement, and type III injuries include posterior displacement. The authors suggest that traction with less than 5 lb can be used under radiographic guidance to reduce and stabilize the injury, but such traction should be immediately discontinued following realignment. With type II injuries, traction should never be used, as this may result in the progression of neurological deficits. Despite these recommendations, these injuries are considered highly unstable; thus most clinicians avoid traction but instead provide immediate halo immobilization and/or internal occipitocervical fixation.

Occipital Condyle Fractures

Occipital condyle injures are relatively rare and often associated with an occipitocervical dislocation. They are frequently unilateral and are often isolated cervical spine injuries in patients with head injuries. If such fractures are not associated with the more ominous AOD, patients usually present without neurological deficit and complain only of upper cervical pain. On plain radiographs, a retropharyngeal hematoma or other soft-tissue swelling may be the only sign of injury. The diagnosis is usually on the basis of computed tomography (CT), and MRI may be useful in determining the extent of associated ligamentous injuries, although this has little utility from a treatment perspective.

Such fractures have also been classified on the basis of their radiographic appearance. CT reveals that type I injuries involve comminution of the condyle without fragment displacement. Type II injuries are characterized by continuation of a basilar skull fracture into the condyle. Type III injuries involve complete avulsion of the condyle and are presumed to result from excessive loading in rotation or lateral bending.⁴

According to the classification scheme originally described by Anderson and Montesano,⁴ the fracture pattern determines treatment. Type II injuries are classified as stable and can be treated with or without a rigid external orthosis for pain control. Types I and III injuries result in ipsilateral alar ligament disruption; thus patients are treated with an external orthosis or a halo vest if the injury is more profound. Surgical intervention is rare but may be indicated when fracture fragments compromise the spinal canal or cause chronic pain as a result of presumed instability.

Atlas (C1)

The atlas supports the skull and allows the greatest range of flexion-extension and rotation in the cervical spine because of its unique articulation with both the occiput and C2, respectively. Injuries to the atlas account for up to 15% of all cervical injuries. There are four major patterns of C1 fracture: burst fracture (Jefferson fracture), posterior arch fracture, lateral mass fracture, and horizontal fracture of the anterior arch. In addition, atlantoaxial dislocations can occur with ligamentous injury.

C1 Burst Fracture (Jefferson Fracture)

C1 burst fractures are presumed to result from direct axial loading that causes lysis of both the anterior and posterior arches, leading to spreading of the lateral masses. Neurological injury is rare, owing to pathological enlargement of the spinal canal. Stability is determined by assessing the extent of injury to the transverse ligament of C1. On open-mouth plain film views, the Rule of Spence states that more than 6.9 mm of combined lateral displacement of the lateral masses over the C2 articular pillars represents an indirect measurement indicating that the transverse ligament has been disrupted.⁵ Such an injury can be confirmed by noting ligamentous disruption on MRI scans.⁶ With disruption, the patient may require surgical stabilization if there is purely ligamentous injury; however, some think that if the ligament is intact and the disruption occurs because of a small bony avulsion off C1, then immobilization with a rigid collar or halo vest can be used with the goal of the avulsion fracture’s re-fusing to C1.

C1 Posterior Arch Fracture

Posterior arch fractures are caused by a compression-hyperextension injury, which results in the occiput’s compressing the posterior arch. Like Jefferson fractures, the canal diameter is usually increased in these injuries, rendering patients neurologically intact. These injuries are relatively stable and thus can be safely treated with the patient in a cervical collar.

C1 Lateral Mass Fracture

It is presumed that axial loading and lateral bending may result in lateral mass fracture at C1. These injuries may be seen on odontoid view radiographs, but CT is the preferred method of detection. Minimally displaced injuries (less than 2 mm) can be treated with a rigid cervical collar; otherwise, halo immobilization or internal fixation may be required.

Horizontal Fractures of the Anterior Arch

Horizontal anterior arch fractures, which are relatively rare, are avulsion injuries due to the superior attachment of the longus colli. These fractures heal well with conservative treatment with the patient in a rigid cervical collar.

Atlantoaxial Instability

Traumatic atlantoaxial instability is secondary to rupture of the transverse ligament of C1, resulting in an increase in the atlantodental interval (ADI). The ADI is measured from the posterior aspect of the anterior arch of C1 to the anterior aspect of the odontoid process. In adults, an ADI less than 3 mm is considered normal. An ADI between 3 and 5 mm suggests transverse ligament disruption. An ADI greater than 5 mm suggests disruption of both the transverse and accessory ligaments.⁷ Dickman et al⁶ described two types of isolated transverse atlantal ligament injuries identified on MRI studies. Type I involves ligament injury without associated fracture of the atlas, and type II involves an avulsion fracture of the atlas at the insertion of the transverse atlantal ligament. The authors concluded that patients with type I injuries should be treated with early surgical fixation because of the inherent instability at C1-C2 following ligamentous disruption, whereas type II injuries require rigid external immobilization.

With such ligamentous injury, surgery is indicated to regain stability, and there exist numerous techniques to stabilize the C1-C2 complex. The original techniques of Gallie,⁸ Brooks and Jenkins,⁹ and Dickman et al¹⁰ involve placing a structural bone graft between the C1 arch and C2 spinous process and supplementing it by posterior wiring around C1 and C2. Although they are rigid in flexion-extension, these constructs are less stable in rotation and require halo immobilization. More recently, techniques involving screw fixation have been developed that provide added stability in all loading modes. C1-C2 transarticular screws directly fix the C1-C2 joints bilaterally. They were originally used in conjunction with posterior wiring techniques. Unfortunately, such screws can be challenging to place, as the course of the vertebral artery may be prohibitive in relation to the screw trajectory. More recently, posterior screw-rod constructs based on the method of Harms and colleagues¹¹ have gained popularity In these constructs, C1 lateral mass screws are attached to screws in the C2 pedicle, the pars interarticularis, or the laminae.

Axis (C2)

The odontoid process (dens) of the axis allows articulation with C1. Some theorize that during developmental formation, there may be an inherent weakness between the C2 body and the dens, as the latter originates from a separate cartilaginous growth center. Incomplete fusion at this junction is termed an os odontoideum, which is believed to be congenital. Others hypothesize that such a floating fragment is the result of a previous fracture at this junction. Full cortication of the fragment may help distinguish this abnormality radiographically from an acute odontoid fracture.

Odontoid Fracture

Odontoid fractures are relatively common cervical fractures and have been classified into three types by Anderson and D’Alonzo.¹² Type 1 fractures occur at the tip of the dens and are considered avulsion fractures of the alar ligaments. Although relatively rare, these injuries are considered stable and heal well with a rigid collar. Type 2 fractures occur through the odontoid process and are generally considered unstable injuries. Type 3 fractures occur in the cancellous bone of the C2 body. These are more stable than type 2 fractures and usually heal with 12 weeks of immobilization.

Type 2 fractures may be challenging to treat. Nonoperative treatment may be attempted, as many of these fractures occur in the elderly. Treatment may include closed reduction prior to stabilization in an external orthosis. Immobilization is associated with a 68% bony union rate, and factors implicated in lower fusion rates include increased age, greater displacement of the fracture plane at final reduction, and a history of smoking. Enthusiasm for halo use in the elderly must also be tempered by a high medical complication rate, as mobility, nutrition, and sanitation are greatly compromised. Although a rigid cervical collar does not provide the same degree of immobilization, it may be preferable in certain instances.

Operatively, anterior screw fixation leads to a higher rate of fusion than the use of an external orthosis (Figure 174-1). However, three anatomical characteristics may affect the technical success of screw placement. First, the patient cannot be significantly kyphotic in the cervical or cervicothoracic spine, as this will prevent the surgeon from obtaining the correct trajectory to place the screw. Second, the fracture fragment must be straight or angled posteriorly so that while the surgeon is reducing the fragment to the C2 body using a lag screw, the fracture planes can be opposed. Third, a comminuted fracture or a poorly angled fracture may not be satisfactorily realigned with the anterior screw and thus may never heal. In these cases, a posterior fusion may be appropriate, using a C1-C2 construct to stabilize the fractured axis.

FIGURE 174-1 Images of a type II odontoid fracture prior to and following stabilization with an anterior odontoid screw. (A) Preoperative sagittal computed tomographic scan. (B) Postoperative lateral cervical radiograph.

Posterior Element and Hangman’s Fracture

A Hangman’s fracture is the result of a traumatic spondylolisthesis of C2 and can be considered a bilateral pars or pedicle fracture (Figure 174-2). This injury was initially attributed to the pathology sustained during judicial hangings, but motor vehicle accidents and falls currently account for the majority of injuries. Effendi et al.¹³ classified these injuries on the basis of the degree of displacement and angulation of C2 relative to C3. Type 1 fractures are not displaced and have no angulation. Type 2 injuries involve more than 3-mm translation, and a subtype, type 2A, involves significant angulation but minimal translation. Type 3 injuries involve severe angulation and translation and may involve unilateral or bilateral facet dislocation. Although surgery is indicated in cases of severe angulation, which is associated with C2-C3 disc or posterior articular disruption, types 1 and 2 may be treated effectively with external fixation (halo or rigid cervical collar).

FIGURE 174-2 Sagittally reconstructed computed tomographic image showing one side of a bilateral type I C2 pars injury (Hangman’s fracture).

Body and Complex

C2 body fractures have also been classified on the basis of their morphology. Type 1 fractures lie in the coronal plane, type 2 fractures in the sagittal plane, and type 3 fractures in the axial plane. Most importantly, these fractures are often associated with significant ligamentous injury and thus should be assumed to be unstable, often requiring surgical stabilization.

Subaxial Spine

In adults, injuries to the subaxial cervical spine occur most frequently at C5 and below because the instantaneous moment of internal rotation between the head and the rigid thoracic spine lies in this area. Children have proportionally more massive heads and thus the moment is more cephalad, leading to a higher rate of high cervical injuries in children. Recently, Vaccaro et al.¹⁴ proposed a subaxial cervical spine injury classification system that shows early signs of validity and reliability. In their classification system, they evaluated three main parameters of injury, including morphology, disruption of the disco-ligamentous complex, and neurological status. The overall injury score is obtained by summing the scores from each category (Table 174-1). A higher score corresponds to an increased likelihood of the need for surgical intervention. The following sections describe the classic injury patterns of the subaxial cervical spine.

Table 174-1 Parameters of the Subaxial Cervical Spine Injury Classification System

Parameters	Points
Morphology
No abnormality	0
Compression	1
Burst	+1 = 2
Distraction (facet perch, hyperextension)	3
Rotation and/or translation (facet dislocation, unstable teardrop or advanced-stage flexion compression injury)	4
Disco-ligamentous complex
Intact	0
Indeterminate (isolated interspinous widening, MRI signal change only)	1
Disrupted (widening of disc space, facet perch or dislocation)	2
Neurological status
Intact	0
Root injury	1
Complete cord injury	2
Incomplete cord injury	3
Continuous cord compression in setting of neurological deficit	+1

From Vaccaro et al.¹⁴

Compression Fracture

Burst Fracture

Cervical burst fractures are defined radiographically by the collapse of the anterior and posterior walls of the vertebral body. Burst fractures are unstable injuries that must be immobilized. Canal compromise and neurological deficit may result from fragment retropulsion. Depending on the clinical scenario and the degree of canal compromise, this can be done with traction or open reduction and instrumented fixation. If posterior ligamentous injury is suspected, surgical stabilization is definitely indicated. In general, anterior corpectomy with reconstruction should be considered. However, when posterior ligamentous injury occurs, posterior supplemental fixation is recommended.

Teardrop Fracture

“Classic teardrop fractures” get their name from the teardrop-shaped chip across the anteroinferior aspect of the vertebral body, presumably as a result of hyperflexion or extreme axial loading when the spine is in a flexed position. Posterior ligamentous injury due to hyperflexion often occurs concomitantly, resulting in a highly unstable injury. If posterior disruption is present but not detected, these unstable injuries may result in severe neurological deficit that require surgical stabilization. If ligamentous injury is ruled out, however, this small anterior fracture can be considered stable and external immobilization for comfort can be used.

Unilateral Facet Dislocation

Unilateral facet dislocation occurs with flexion-rotation injury and involves the inferior articular facet of the upper vertebrae’s dislocating anterior to the superior articular process of the lower vertebrae, resulting in “locked” facets. In some cases, the inferior articular process sits directly superior to the inferior articulating process in a “perched” fashion. Radiographically, usually a less than 25% anterolisthesis of the rostral vertebral body is seen on lateral plain films, rotation of the spinous processes on anteroposterior films to one side, and the dislocation of facets noted on oblique x-rays. CT is an ideal imaging modality for determining the extent of facet fracture (Figure 174-3).

FIGURE 174-3 Sagittally reconstructed computed tomographic images showing unilateral perched facets at C5-C6 and C6-C7 at midline (left), parasagittal (center), and lateral (right).

Unilateral facet dislocations often result in neurologic injury due to nerve root compression. These dislocations are considered unstable injuries and require reduction and fixation. Closed reduction with traction can be attempted, and, if successful, an external immobilization device can be used. However, in cases where external reduction cannot be achieved, open reduction and internal fixation are required.

There is a great deal of debate on the utility of prereduction MRI in patients who will undergo traction. Reports in the literature include cases of patients’ conditions deteriorating following traction as a result of a previously undiagnosed herniated disc at the injured level.¹⁵ Thus it has been suggested that patients be screened by MRI prior to reduction. However, most clinicians suggest initiating traction as soon as possible in patients with a neurological deficit who can participate by following commands during the reduction process. For patients who are unable to participate because of altered mental status (e.g., head injury), an MRI study should be obtained. It should also be noted that it is often harder to reduce unilaterally locked facets than bilaterally locked facets, and a rotational component may be added during the reduction process to facilitate realignment.

Bilateral Facet Dislocation

Hyperflexion can cause severe posterior ligamentous injury, resulting in bilaterally locked facets. When the bony facets remain intact, this injury can result in severe anterolisthesis and canal compromise and thus is most commonly associated with a neurological deficit (Figure 174-4). On plain films, 50% or greater subluxation of the vertebral body may be seen, and angular deformity is common. As with unilateral facet dislocation, it is advisable to attempt traction reduction to realign the spinal column prior to attempting fixation. The same concerns apply with regard to an underlying herniated disc. Because of the severity of destabilization and commonly associated neurological dysfunction, combined anterior-posterior fixation should be considered in these patients.

FIGURE 174-4 Images of a patient with C3-C4 bilateral jumped facets. (A) Lateral plain film shows anterolisthesis of C3 on C4. (B) T2-weighted sagittal MRI scan shows subluxation with spinal cord compression.

Hyperextension Injury

Hyperextension injuries can take the form of dislocation, fracture-dislocation, or laminar injuries. Radiographically, spinal alignment may appear normal and bony anatomy may be intact, but severe injury to the disc and posterior ligamentous complex may be present. Prevertebral soft-tissue injures, widening of the intervertebral spaces, and irregularity or horizontal fractures of the vertebral end plates may be seen. Because of extensive disco-ligamentous disruption, such injuries are considered highly unstable. Central cord syndrome may be a common finding, especially in association with cervical spondylosis. Similarly to a nonbony Chance fracture ¹⁶ in the thoracolumbar region, it is unlikely that a dislocation through the disc space will heal and fusion will be required, which may be achieved by both anterior and posterior fixation.

In the absence of ligamentous injuries, laminar fractures are considered stable. Thus isolated laminar fractures with intact facet joints and anterior column can be treated with a rigid orthosis for comfort.

Clay-Shoveler’s Fracture

The classic clay-shoveler’s fracture was mechanistically described as an avulsion of the spinous process.¹⁷ Such an injury occurs while shoveling clay, which sticks to the shovel and causes the trapezius to pull strongly on the spinous process when a the shovel is thrust forward. This injury most commonly occurs at C7 and less frequently at C6 and T1 (Figure 174-5). At present, this injury typically occurs as a result of a direct blow to the spinous processes. This is considered a stable fracture and can be treated by placing the patient in an external orthosis for pain control.

FIGURE 174-5 Clay shoveler’s fracture at C7 on a lateral cervical plain film.

Penetrating Injuries

Overall, penetrating injuries account for roughly 12% of all spinal injuries in the United States. However, the incidence may increase to up to 40% in some metropolitan centers, with young males being the most common victims. The mechanism of injury is important. Although gunshot victims are more than twice as likely as stabbing victims to have a functional spinal cord transection, knife wounds are more likely than gunshot wounds to be contaminated. In either case, structural stability and neurological injury vary. Treatment in all cases must be geared toward treating spinal instability, infection, arterial injury, and dural disruption. Operative intervention to stabilize, repair, and remove foreign bodies or bony fragments can be considered. However, it is generally agreed that bullet fragments should be left in place if not associated with active or progressive problems (e.g., cerebrospinal fluid leak, hematoma). Injury to any structure along the path of the projectile must be considered and investigated.

Spinal Cord Injury

As stated above, there are a number of injury patterns that lead to severe spinal column instability and thus have the potential for inducing damage to the cord. In evaluating spinal cord injury, the first step is to define whether the injury is complete or incomplete. Classically, a complete spinal cord injury was thought to be a lack of conscious sensation and voluntary muscle control below the site of the injury. However, such a description is misleading because partial preservation, including lateral preservation, of function below the injury site is rather common. In addition, a delayed return of function may occur in the first few days after the injury, even after an initial determination that the injury is complete. Therefore, in the case of a complete motor injury, sensation and bladder and/or bowel dysfunction must be assessed. In 1992, the American Spinal Injury Association (ASIA)¹⁸ defined a complete spinal cord injury as one that yields no sensory or motor function in the perineal and anal regions (S4-S5). A scale has also been created that calculates a score based on motor and sensory evaluation of the entire body (Figure 174-6).¹⁹ Motor evaluation may yield a maximum of 50 points for the upper extremities and 50 points for the lower extremities. Sensation can yield a total of 112 points for both pinprick and light touch sensation. Following this evaluation, the ASIA Impairment Scale classifies the patient’s condition into one of five categories (A through E), in which A is a complete injury, B through D are incomplete, and E is normal sensory and motor function (Table 174-2).

FIGURE 174-6 American Spinal Injury Association (ASIA) evaluation form. Available at http://www.asia-spinalinjury.org/publications/59544_sc_Exam_Sheet_r4.pdf.

Table 174-2 American Spinal Injury Association (ASIA) Impairment Scale

Grade	Classification	Description
A	Complete	No motor or sensory function is preserved in the sacral segments S4-S5.
B	Incomplete	Sensory but not motor function is preserved below the neurological level and includes the sacral segments S4-S5.
C	Incomplete	Motor function is preserved below the neurological level, and more than half of the key muscles below the neurological level have a muscle grade <3.
D	Incomplete	Motor function is preserved below the neurological level, and more than half of the key muscles below the neurological level have a muscle grade of ≥3.
E	Normal	Motor and sensory function are normal.

Complete Spinal Cord Injury

Such injuries can be devastating to patients, leaving them with possible paralysis of all limbs and the inability to breathe if they have high cervical cord injuries (at or above C3). Management includes spinal stabilization to facilitate nursing and rehabilitation. In most cases of surgical decompression, the goals of surgery are centered on maintaining or regaining function in the uppermost section of the injured cord, an area in which an incomplete injury may exist. Beyond surgery, care is centered on functional rehabilitation, prevention of decubitus ulcers, bowel and bladder management, and avoidance of pneumonia and deep vein thrombosis.

Incomplete Spinal Cord Injury

As shown previously in describing the Vaccaro et al.¹⁴ classification system, incomplete injuries are weighted more heavily than complete injuries or normal neurological function with regard to the need for surgical intervention. This is mainly because open or closed reduction and cord decompression can allow the patient to maintain or regain neurological function if done expediently. The following sections describe some of the classic incomplete spinal cord syndromes.