There are currently more than 200,000 patients living with spinal cord injury (SCI) in the United States, and between 12,000 and 20,000 new cases occur on an annual basis. The majority of patients are between 16 and 30 years of age, with motor vehicle collisions, falls, violence, and sporting injuries accounting for the bulk of cases. Fewer than 1% of patients experience complete neurologic recovery before hospital discharge, and the associated economical, physical, and emotional tolls are astronomical.
The cervical spine is composed of 7 cervical vertebrae, the first 2 of which are unique, whereas the remaining 5 (C3 through C7) are functionally similar. The anatomy of the axis (C1) is that of a bony ring without a true vertebral body. It consists of an anterior and posterior arch joined together by 2 lateral masses that articulate with the occipital condyles above and C2 below. The Atlas (C2) has a unique anterior body that extends superiorly to form the odontoid process. This structure articulates with the internal surface of the anterior ring of C1 and is held in place by the transverse ligament. The unique design of these 2 vertebrae allow for the increased flexibility and axial rotation of the upper cervical spine. The remaining cervical vertebrae are functionally similar and composed of an anterior body and a posterior arch.
The vertebrae are separated by flexible intervertebral disks and linked together by an intricate system of ligaments that allows the spine to function as a single unit. Anterior and posterior longitudinal ligaments run along the entire length of the vertebral bodies, whereas the posterior rings are linked together by the ligamentum flavum and interspinous ligaments (Figure 86-1). This network enables significant spinal column mobility while still providing adequate spinal cord protection as it courses within the spinal canal between the body and arch of each vertebra. External forces that exceed the normal physiologic range of motion can result in fractures, dislocations, and spinal cord injuries. Children and the elderly are especially prone to injury of the upper cervical spine (C1 through C3), whereas young and middle-aged adults are more likely to injure the lower cervical spine (C6 through T1). Of the cervical vertebrae, the atlas (C2) is the most frequently fractured.
Bony and ligamentous anatomyof the spine. Reprinted with permission from Tintinalli JE, Kelen GD, Stapczynski JS. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York: McGraw-Hill, 2004.
Delineating between stable and unstable injury is of supreme clinical importance. The Denis 3-column theory is very helpful in this regard and divides the spine into 3 functional units. The anterior column is composed of the anterior portions of the vertebral body and annulus fibrosis together with the anterior longitudinal ligament. The middle column includes the posterior vertebral body, the posterior annulus fibrosis, and the posterior longitudinal ligament. The posterior column is composed of the posterior vertebral arch and the posterior ligamentous complex including the ligamentum flavum and the interspinous and supraspinous ligaments. Injuries to ≥2 of the columns are considered functionally unstable. In addition, acute compression fractures involving >25% of the height of the vertebral bodies of C3–C7 are considered clinically unstable.
Cervical spine fractures can be further classified by their mechanism of injury (Table 86-1). Flexion injuries compress the anterior column and distract the posterior column, resulting in anterior body fractures and disruption of the posterior ligamentous complex. Specific examples include anterior subluxations, bilateral facet dislocations, simple wedge fractures, spinous process avulsions (clay shoveler's fracture), and flexion teardrop fractures. A concurrent rotational mechanism results in unilateral facet dislocations. Simple wedge fractures, spinous process avulsions, and unilateral facet dislocations are generally considered stable, whereas the remainder represent unstable injuries.
Stability of cervical spine injuries.
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Stability of cervical spine injuries.
|Anterior subluxation (hyperflexion sprain) (stable)* |
|Bilateral interfacetal dislocation (unstable) |
|Simple wedge (compression) fracture (usually stable) |
|Spinous process avulsion (clay-shoveler's) fracture (stable) |
|Flexion teardrop fracture (unstable) |
|Unilateral interfacetal dislocation (stable) |
|Pillar fracture |
|Fracture of lateral mass (can be unstable) |
|Vertical compression |
|Jefferson burst fracture of atlas (potentially unstable) |
|Burst (bursting, dispersion, axial-loading) fracture (unstable) |
|Hyperextension dislocation (unstable) |
|Avulsion fracture of anterior arch of atlas (stable) |
|Extension teardrop fracture (unstable) |
|Fracture of posterior arch of atlas (stable) |
|Laminar fracture (usually stable) |
|Traumatic spondylolisthesis (hangman's fracture) (unstable) |
|Lateral flexion |
|Uncinate process fracture (usually stable) |
|Injuries caused by diverse or poorly understood mechanisms |
|Occipital condyle fractures (can be unstable) |
|Occipitoatlantal dissociation (highly unstable) |
|Dens fractures (type II and III are unstable) |
Extension injuries compress the posterior column and distract the anterior column, resulting in crush injuries to the posterior elements and disruption of the anterior longitudinal ligament. Specific examples include extension teardrop fractures, hangman's fractures (traumatic spondylolisthesis of C2), laminar fractures, and hyperextension dislocations. With the exception of simple laminar fractures, these injuries are generally unstable.
Axial load injuries occur when vertical compression forces shatter the ring-like structure of a cervical vertebra, resulting in an outward burst of bony fragments. These injuries require disruption of all 3 columns and are clinically unstable. Burst fractures of C1 (Jefferson fracture) are relatively common and highly unstable.
Any significant trauma to the spinal cord generally occurs at the time of the initial injury. Although individual injuries will frequently exhibit unique neurologic findings, several classic syndromes have been described. The central cord syndrome occurs with hyperextension mechanisms, typically in elderly patients with severe spinal stenosis. It presents with motor weakness that is more pronounced in the upper extremities as compared with the lower. The anterior cord syndrome occurs with hyperflexion mechanisms and results in motor and sensory loss below the level of injury with preservation of position and vibratory sense (located in the posterior columns). The Brown-Sequard syndrome most commonly stems from a penetrating injury that hemisects the cord. Classic findings include the ipsilateral loss of motor function and position and vibratory sensation combined with the contralateral loss of pain and temperature sensation distal to the lesion.
Spinal cord injury without radiologic abnormality (SCIWORA) is seen in pediatric patients and should be considered in all patients with neurologic findings despite negative initial plain film or computed tomography (CT) imaging. Magnetic resonance imaging (MRI) may reveal significant pathology, including ligamentous injury, intracordal edema, and hemorrhage.