Classification of Neurologic Injury

Determining the extent of a neurologic deficit in a patient with a spinal cord injury is paramount to understanding the overall prognosis. A complete injury is one in which “no motor or sensory function exists more than three segments below the level of the injury.” Incomplete injuries retain some neurologic function further than three segments below the level of the injury with the caudal segment exhibiting greater than 60% motor strength and intact sensation.

Patients with complete injuries have less than a 3% chance of motor recovery in the first 24 hours. Patients with sacral sparing have partial continuity of the white matter long tracts and demonstrate an incomplete cord injury. The presence of the bulbocavernosus reflex, a spinal reflex mediated by the S3-S4 region of the conus medullaris, may be absent in the first 4–6 hours after injury while the patient is in “spinal shock,” but usually returns within 24 hours. If the reflex does not return after 24 hours and distal neurological function remains absent, the injury is complete.

The secondary survey in patients with spinal cord injury includes a precise definition of neurologic deficits. Classification systems are useful to compare outcomes between different studies. While a variety of clinical grading systems exist, the American Spinal Injury Association (ASIA) scale has become the most widely accepted. The ASIA scale identifies motor, sensory, and general impairment deficits, and incorporates the functional independence measure (see page 163).

Incomplete Spinal Cord Syndromes

Four incomplete spinal cord syndromes are defined based on the location of the trauma to the spinal cord. Central cord syndrome is the most common pattern of injury, resulting from gray matter destruction, which is worst in the central region of the spinal cord. This injury pattern often occurs due to hyperextension injury in a patient with degenerative cervical spinal stenosis. The patient experiences motor and sensory deficits that are worse in the upper than in the lower extremities. The overall prognosis for central spinal cord injuries is good, with 75% of the patients experiencing at least partial motor recovery and most regaining the ability to ambulate.

Anterior cord syndrome is caused by vascular injury to the anterior portion of the spinal cord that causes motor/sensory deficits (lower greater than upper) with sparing of proprioception and position sense. This diagnosis carries the worst prognosis with only 10% of patients regaining substantial function.

Brown–Sequard syndrome is caused by isolated injury of one lateral half of the spinal cord and results in ipsilateral motor and contralateral sensory deficits. This syndrome has the best functional recovery.

Posterior cord syndrome is the rarest and causes decreased position and pressure sensation.

Spinal Cord Injury

Pharmacologic intervention for spinal cord injury continues to be a controversial topic. The recommended protocols based on the National Acute Spinal Cord Injury Study are a 30 mg/kg loading dose and 5.4 mg/kg/hr of methylprednisolone for 23 hours when delivered within 38 hours of injury, and a 47-hour infusion when started within 8 hours of injury. Despite the high acuity of these studies, the differences in the outcome are small, and bleeding and infectious complications were high in the steroid group compared to the control group. As a result, most spine societies do not regard these steroid protocols as an essential feature of initial spinal cord injury management.

Evaluation

Cervical spine clearance for trauma patients continues to be a topic of debate. Class I evidence suggests that cervical spine radiographs are necessary for patients who present with neck pain or tenderness and have a decreased level of consciousness or are intoxicated, or who have distracting injuries. A cervical spine series consisting of anteroposterior (AP), lateral and open-mouth odontoid views has 85% sensitivity. The addition of flexion-extension views in the awake and alert patient to delineate spinal instability increases the negative predictive value to 99%.

It is important that radiographs include the C7-T1 interspace to identify any pathology around the cervicothoracic junction. The AP radiograph should be evaluated for symmetric disk height, lateral mass alignment, and spinous process orientation. The lateral radiograph should exhibit smooth anterior and posterior vertebral lines and spinolaminar lines as well as symmetric disk spaces and overlap of the lateral masses. Soft tissue planes should be evaluated and should be less than 6 mm at C2 and less than 2 cm at C6.

Computed tomography (CT) is useful to identify osseous pathology not seen on radiographs and is especially helpful at the craniocervical and cervicothoracic junctions. In some centers, CT scanning with sagittal and coronal plane reconstructions is replacing plain radiography as a screening study for high energy trauma admissions. Magnetic resonance imaging (MRI) may also be helpful in limited situations to diagnose soft tissue injury, such as the ligaments, disks, and facet capsules.

Anatomy

The cervical spine consists of seven vertebrae, and is subdivided into the atlas (C1), axis (C2), and subaxial spine (C3-C7). The atlas is ring-shaped, consisting of two articular lateral masses without a body or spinous process. The axis contains the odontoid process, which articulates with the anterior arch of the axis. The transverse ligament stabilizes this joint.

The subaxial spine consists of vertebral bodies with concave superior endplates. The facet joints are encapsulated synovial joints with overlying hyaline cartilage. The facet joint angle is 45 degrees in the sagittal plane.

Spinal stability primarily stems from ligament and disk integrity. Craniocervical stability involves intact anterior and posterior atlanto-occipital membranes and articular capsules. The atlantoaxial joint is stabilized by the transverse ligament primarily with the paired alar and apical ligaments provided secondary stabilization. The posterior ligamentum nuchae, interspinous ligaments, and ligamentum flavum acts as a “tension band” to provide resistance against flexion distraction injuries. The atlantoaxial joint provides 50% of the overall cervical rotation (Figure 2).

Figure 2 Sagittal cervical spine cross-section.

(Data from Heller J, Pedlow F: Anatomy of the cervical spine. In Clark CR, Dvorak J, Ducker TB, et al., editors: The Cervical Spine, 4th ed. Philadelphia, Lippincott-Raven, 2005, p. 9.)

The vertebral artery passes through the vertebral foramina from C6 to C1 and then turns posteromedially around the superior articular process before entering the foramen magnum and joining the basilar artery. The vertebral artery follows a similar course, but enters at the C7 transverse foramina. Unilateral absence or hypoplasia of the vertebral artery is 5%–10%.

The vertebral canal sagittal diameter narrows from 23 mm at C1 to 15 mm at C7. Nerve roots exit the canal through the intervertebral foramen. The posterolateral uncovertebral joint and intervertebral disk forms the anterior border of the foramen while the posterior border is formed by the caudal superior articular facet. The C2 nerve root exits posterior to the C1-C2 facet joint, whereas the remaining cervical nerve roots exit anterior to the facet joints. The spinal nerves pass posterior to the vertebral artery at the middle of the corresponding lateral mass. The cervical plexus consists of the ventral rami of C1 through C4, whereas the brachial plexus is made up from the ventral rami of C5 through T1.

Cervical Spinal Ligamentous Instability

White and Panjabi defined instability as “the loss of ability of the spine under physiologic loads to maintain its pattern of displacement so that there is no initial or additional neurologic deficit, no major deformity, and no incapacitating pain.” Acute radiographic instability criteria of the subaxial cervical spine include greater than 3.5 mm translation or greater than 11 degrees of angulation in the lateral plane. Because of the potential for late instability following the resolution of acute pain and muscle spasm, patients with significant axial neck ache but normal radiographs are indicated for follow-up flexion/extension films at around 2 weeks postinjury.

Occipital Condyle Fracture

Occipital condyle fracture should be considered a marker for potentially lethal trauma as patients experience an 11% mortality rate from associated injuries. Anderson and Montesano classified these fractures into the following types:

Types I and II fractures are caused by axial loading and have intact alar and tectoral membrane ligaments. Type III fractures are caused by skull distraction and have ligamentous disruption.

Stable type I, II, and III fractures can be managed in a cervical collar for 6–8 weeks. Displaced type II or III fractures are managed in a halo vest for 8–12 weeks. Grossly unstable type III fractures require occiput to C2 fusion and should raise the suspicion for an underlying occipitocervical dissociation. Cranial nerve palsies may develop days to weeks after the injury and most frequently involve cranial nerves IX, X, and XI (Figure 3).

Figure 3 Types of occipital condyle fractures.

(From Anderson PA, Mirza SK, Chapman JR: Injuries to the Atlantooccipital articulation. In Clark CR, Dvorak J, Ducker TB, et al., editors: The Cervical Spine, 4th ed. Philadelphia, Lippincott-Raven, 2005, p. 594.)

Occipitocervical Dissociation

Occipitocervical dissociation (OCD) injuries have a high mortality rate. Patients who survive this injury demonstrate a wide variety of neurological sequelae ranging from cranial nerve palsies affecting VI, X, and XII, and cord lesions. OCDs are classified as I, anterior; II, longitudinal; and III, posterior.

Radiographic diagnosis of OCD can be evaluated by the Powers ratio, which divides the basion to posterior arch distance by the anterior arch to opisthion distance. A Power’s ratio greater than 1.0 suggests anterior dissociation. Another radiographic measure known as Wachenheim’s line can help evaluate for anterior or posterior subluxation. A line along the posterior surface of the clivus and extended caudally should just touch the posterior aspect of the tip of the dens. If this line runs anterior to the dens, anterior subluxation of the occipital condyles has occurred, while a position posterior to the dens indicates posterior subluxation.

The diagnosis can be difficult to make due to poor visualization of the osseous detail. The reported sensitivity for diagnosing OCD on plain radiographs is 57%, CT 84%, and MRI 87%. Treatment of OCD injuries requires instrumented occipitocervical fusion to at least C2, frequently augmented with halo vest placement.

Atlas Fractures

Atlas fractures comprise 7% of the cervical spine fractures. Fractures can involve the anterior or posterior arch, lateral masses, and transverse processes. Jefferson or burst fractures are bilateral, involving both the anterior and posterior arches resulting from axial load (Figure 4). Atlantoaxial stability depends on the integrity of the transverse ligament. Combined lateral mass displacement greater than 7 mm on AP radiographs (Figure 5).

Figure 4 Types of C1 arch fractures.

(From Hasharoni A, Errico TJ: Fracture of the first cervical vertebra. In Clark CR, Dvorak J, Ducker TB, et al., editors: The Cervical Spine, 4th ed. Philadelphia, Lippincott-Raven, 2005, p. 610.)

Figure 5 Radiographic assessment of transverse ligament instability.

(From Hasharoni A, Errico TJ: Fracture of the first cervical vertebra. In Clark CR, Dvorak J, Ducker TB, et al., editors: The Cervical Spine, 4th ed. Philadelphia, Lippincott-Raven, 2005, p. 592.)

Magnetic resonance imaging is a more sensitive means of detecting transverse ligament injury with mid-substance (type I) injuries having a poorer healing response than avulsion fractures (type II). Thus, type I injuries often require a C1-C2 arthrodesis, while type II injuries generally heal with halo vest immobilization. Most atlas fractures are stable and can be treated nonoperatively with 6–12 weeks of immobilization in a cervical collar.

Dens Fractures

Dens fractures have been classified by Anderson and D’Alonzo (Table 1; Figure 6). Type I and III fractures can generally be treated with an external orthosis. Management of type II fractures is more problematic and depends on patient age and associated injuries, as well as fracture displacement and stability. While nondisplaced fractures can sometimes be treated successfully with a halo vest, indications to operate include fracture comminution, displacement greater than 6 mm, posterior angulation, delay in diagnosis, and patient age greater than 50 years old. In general, elderly patients can be considered for C1-C2 fusion because of their decreased healing rates and poor tolerance of halo vest. Severely debilitated patients, on the other hand, can be treated with a cervical collar until comfortable, with the understanding that a successful fusion may not occur.

Table 1 Classifications of Dens Fractures

Source: Anderson LD, D’Alonzo RT: Fractures of the odontoid process of the axis. J Bone Joint Surg 56:1663–1674, 1974.

Figure 6 Types of odontoid fractures.

(From Anderson LD, D’Alonzo RT: Fractures of the odontoid process of the axis. J Bone Joint Surg 56:1663–1674, 1974.)

Surgical treatment can also be performed via anterior odontoid screw osteosynthesis, particularly for oblique fractures that run from anterosuperior to posteroinferior, patients with C1 ring fractures, and younger patients. C1-C2 arthrodesis can be performed via several techniques including wiring, transarticular screws, or rod and screw constructs.

Traumatic Spondylolisthesis of Axis

Bilateral fractures of the par interarticularis are called hangman’s fractures. Most injuries are caused by motor vehicle accidents. Hangman’s fractures are classified by Levine and Edwards (Table 2; Figure 7). Type I fractures require 6–12 weeks of halo vest immobilization. Surgical options for type II and III fractures include reduction followed by anterior C2-C3 interbody fusion, posterior C1-C3 fusion, or bilateral C2 pars screw osteosynthesis.

Table 2 Classifications of Hangman’s Fractures

Source: Levine AM, Edwards CC: The management of traumatic spondylo-listhesis of the axis. J Bone Joint Surg 67:221–226, 1985.

Figure 7 Types of Hangman’s fractures.

(From Levine AM, Edwards CC: The management of traumatic spondylolisthesis of the axis. J Bone Joint Surg 67:221–226, 1985.)

Subaxial Spine Fractures

Isolated fractures of the spinous process, lamina, and transverse processes occur frequently, and are most often stable as long as the facet articulations are competent and minimal vertebral translation has occurred.

Subaxial cervical spine fractures can be subclassified many ways. The most common injuries include compression, burst, and teardrop injuries.

Compression flexion injuries cause failure to the anterior half of the vertebral body without disruption of the posterior body cortex. The mechanism is a hyperflexion or axial loading injury. Patients are usually neurologically intact and in the absence of gross deformity or instability, most fractures heal with external immobilization in 6–12 weeks.

Burst fractures involve the anterior and middle columns and may extend into the posterior body cortex. Burst fractures that do not involve the posterior elements are more stable and can be treated in a halo for 12 weeks. Fractures that involve the posterior elements are unstable and can be associated with cord compromise. These types of fractures require anterior surgical decompression and stabilization via an anterior plate or added posterior fixation if necessary.

Extension tear drop injuries occur with hyperextension of the neck with an avulsion fracture of the anteroinferior vertebral body. This injury typically occurs at the C2-C3 interspace. Most of these injuries can be treated with a cervical collar for 6–8 weeks, even if the anterior longitudinal ligament has been disrupted. Flexion teardrop injuries are a more severe injury and may be associated with spinal cord injury. The teardrop fracture is located at the anteroinferior corner of the body, with the posteroinferior corner of the body rotating into the canal and possibly causing an anterior cord syndrome. Initial treatment consists of tong application for spinal reduction. Anterior decompression may be necessary to address cord compromise along with anterior and/or posterior stabilization.

Subaxial Spine Dislocations

Unilateral dislocations demonstrate 25% vertebral subluxation with associated monoradiculopathy that improves with traction. Bilateral dislocations demonstrate vertebral body subluxation greater than 50% without significant spinal cord injury. Awake and alert patients can safely undergo closed reduction with progressive application of traction as long as serial neurologic exams and radiographic assessments are taking place. A successful closed reduction without significant kyphotic deformity or radiculopathy can be managed with 6–12 weeks of external immobilization.

Patients who develop new or worsening neurologic deficits while having a closed reduction should proceed to have an MRI to identify a possible herniated disk. Overall, 25% of patients will fail a closed reduction will demonstrate signs of disk disruption on MRI. Patients who fail a closed reduction maneuver will require an open reduction and instrumented fusion. Additionally, patients with kyphotic deformity, significant subluxation, radiculopathy, bilateral facet fractures, and lateral mass dissociations may be treated with anterior or posterior instrumented fusions.

Special Considerations

Children less than 10 years of age frequently have spine injuries from the occiput to the third cervical spine due to the weight/size of the head being proportionally larger than the body. Children older than 10 years of age have spinal injuries similar to adults. Elderly patients frequently exhibit C1-C2 injuries that include transverse ligament disruption and dens fractures.

Anatomy

The thoracic spine is more rigid than the cervical or lumbar spine due to attachments of the ribs to the transverse processes and vertebral bodies. The thoracic spine also imparts its overall stability from the coronally orientated facets with shingled lamina, properties that limit extension. Because of the rigidity of the thoracic spine, the transition zones at T1 and T12 are highly susceptible to injury.

The thoracic spine has an overall kyphotic alignment with the apex centered around T6 through T8 with a range of 15–49 degrees. Maximal anterior column forces are generated and fractures within the rib cage usually occur at this location.

Motorcyclists have a high prevalence for blunt chest and throracic spine trauma. Patients with lap belt echymosis are also at higher risk for flexion distraction T-L injuries.

Fractures

Denis’s three-column concept is frequently used because it includes the injury patterns most commonly seen and relates them to a specific mechanism of injury. The classification includes both minor and major injuries. Minor injuries include isolated fractures to the articular process, transverse process, and pars interarticularis. Major fracture types include compression, burst, flexion distraction, and fracture dislocations (Figure 8).

Figure 8 Spinal columns. SSL, Supraspinal ligament; PLL, posterior longitudinal ligament; ALL, anterior longitudinal ligament; AF, annulus fibrosus.

(Adapted from McAfee PC, Yuan HA, Fredrickson BE, Lubicky JP: The value of computed tomography in thoracolumbar factures: an analysis of one hundred consecutive cases and a new classification. J Bone Joint Surg 65:461–473, 1983, with permission.)

Compression Fractures

A compression fracture results from an axial load involves the anterior column of the spine. Radiographs show a wedge shaped defect in the vertebral body with varying degrees of kyphosis. Patients who are neurologically intact with less than 30 degrees of kyphosis and less than 50% vertebral body height loss can be managed in a hyperextension orthosis. Patients who do not meet these criteria need to be watched carefully for possible failure of the posterior ligamentous structures. Patients with fractures above T6 should wear a cervical extension for better spinal control (Figure 9).

Figure 9 Compression fracture.

(From Holdsworth FW: Fractures, dislocations and fracture-dislocations of the spine. J Bone Joint Surg Br Dec 52(8):1534–1551, 1970).

Burst Fractures

Burst fractures also occur from axial loads but involve the anterior and middle columns. Involvement of the posterior column equates to overall instability. Radiographically, burst fractures demonstrate widening of the pedicles and varying degrees of retropulsion into the canal. Patients without neurologic deficits, kyphosis less than 30 degrees, and less than 50% vertebral body height loss can be managed with a thoracolumbar orthosis for 3 months. Patients who do not meet these criteria should undergo a posterior instrumented fusion procedure (Figure 10).

Figure 10 Burst fracture.

(From Holdsworth FW: Fractures, dislocations and fracture-dislocations of the spine. J Bone Joint Surg Br Dec 52(8):1534–1551, 1970.)

Flexion Distraction

Flexion distraction injuries occur when the flexion moment occurs anterior to the vertebral column. This injury typically occurs in motor vehicle accidents where the lap belt acts as a fulcrum, and the anterior column fails in compression, whereas the middle and posterior columns fail in tension. Purely ligamentous injuries have a poor propensity to heal and usually require short-segment posterior procedures. Pure bony injuries have the potential to heal without surgical intervention as long as a nonunion or deformity does not occur (Figure 11).

Figure 11 Flexion distraction.

(From Holdsworth FW: Fractures, dislocations and fracture-dislocations of the spine. J Bone Joint Surg Br Dec 52(8):1534–1551, 1970.)