Epidemiology of Cervical Spine Trauma and Spinal Cord Injury

Fractures and dislocations of the spinal column can be devastating injuries, with 10% to 25% of patients experiencing neurologic deficits.^1,2 In patients with cervical spine trauma, up to 40% may have neurologic deficits.³ The NEXUS (National Emergency X-Radiography Utilization Study) group reported a 2.4% incidence of cervical spine injury with a heavy male predominance (64.8%).^4,5 There is a bimodal age distribution for cervical spine injury, with the highest incidences at ages 15 to 45 and 65 to 85.⁶ Motor vehicle accidents, falls, and sporting accidents with direct loading of the head are the most common causes of injury.⁷

The majority of cervical spine injuries occur in the subaxial spine. Two thirds of cervical spine fractures and 75% of dislocations occur in the subaxial cervical spine. Bilateral facet dislocation is a potentially devastating injury and most commonly occurs at C5-6 and C6-7.⁸ Facet dislocations are a major risk factor for spinal cord injury, with complete spinal cord injury and quadriplegia occurring in 50% to 84% of cases with bilateral facet dislocations.^9–13 This highlights the importance of accurate diagnosis and timely treatment of cervical spine injuries.

Neurologic and spinal cord injuries are common in patients with cervical spine trauma; the high cost to society prompted the U.S. Centers for Disease Control and Prevention to establish a system to monitor spinal cord injuries.¹⁴ There were an estimated 12,000 new spinal cord injuries in 2008,¹⁵ and the incidence is expected to increase to 13,400 in 2010.¹⁶ Patients with spinal cord injuries have a shortened life expectancy, with a 10-year survival rate of 86%.¹⁷ The most common causes of death are diseases of the pulmonary and cardiovascular system.^15,18

Advancements in medical treatment and automobile safety have resulted in fewer complete spinal cord injuries and a higher percentage of incomplete injuries.^15,19–21 In the past, diagnosis was often delayed or missed due to poor or inadequate radiographic visualization. Improved and increased use of CT has contributed to more accurate diagnosis and prompt treatment of cervical spine trauma.⁵ Superior seat belt designs and automobile airbags have reduced mortality and injury severity in motor vehicle accidents.^19–24 Fewer cervical fractures and spinal cord injuries occur with proper use of airbags and three-point mechanical restraints.²⁵

Spinal Cord Injuries

Various classification systems have been developed to describe spinal cord injuries. A general method is to describe spinal cord injuries as incomplete or complete. Incomplete injuries have preserved motor or sensory function below the level of injury. However, patients can present only with signs of sacral sparing. Sacral sparing signifies a structural continuity between the sacral motor neurons in the conus medullaris and the cerebral cortex and manifests as perianal sensation, rectal motor function, or great toe flexor activity. Complete spinal cord injuries have total loss of motor and sensory function below the level of injury. A diagnosis of complete spinal cord injury, however, cannot be made until the resolution of spinal shock, a transient state of complete spinal areflexia that typically resolves after 24 hours.²⁶ During spinal shock no spinal cord function is present, including sacral sparing. Return of sacral reflexes such as the S3-4–mediated bulbocavernosus reflex, or anal wink, heralds the end of spinal shock. If no sacral reflexes return after resolution of spinal shock, the injury can be termed a complete spinal cord injury.

Spinal cord injuries can be graded by the American Spinal Injury Association (ASIA) scale.²⁷ The ASIA scale, a modification of the Frankel scale,²⁸ ranks spinal cord injuries from ASIA A through ASIA E. ASIA A designates a complete spinal cord injury with no motor or sensory function below the level of injury. ASIA B, C, and D are categories of incomplete spinal cord injuries. ASIA B indicates an injury with preservation of distal sensory function but no motor function below the level of spinal injury. ASIA C represents a spinal cord injury with a motor function grade of less than 3 out of 5, whereas an ASIA D injury has a motor function grade of 3 or greater. Patients in the ASIA E category have a normal neurologic examination (Table 226-1).

TABLE 221-1 American Spinal Injury Association Impairment Scale

Grade	Spinal Cord Injury	Description of Spinal Cord Injury Pattern
A	Complete	No motor or sensory function below neurologic level
B	Incomplete	No motor function below neurologic level; sensory function present below neurologic level
C	Incomplete	Motor function preserved below neurologic level; at least half of key muscle groups below injured level have a grade less than 3
D	Incomplete	Motor function preserved below neurologic level; at least half of key muscle groups below injured level have a grade 3 or better
E	Normal	Motor and sensory function normal

Adapted from American Spinal Injury Association: Standards for neurological and functional classification of spinal injury—revised, Chicago, 1992, American Spinal Injury Association.

Incomplete spinal cord injuries can also be described by one of several syndromes. These syndromes are based on the anatomic location of the lesion within the spinal cord parenchyma and on clinical presentation (Fig. 226-1).

FIGURE 226-1 Spinal cord syndromes. A, Central cord syndrome. B, Anterior cord syndrome. C, Posterior cord syndrome. D, Brown-Séquard’s syndrome.

(Adapted from Klein GR, Vaccaro AR: Cervical spine trauma: upper and lower. In Vaccaro AR, Betz RR, Zeidman SM, editors: Principles and practice of spine surgery, Philadelphia, 2003, Mosby, p 442.)

The most common incomplete spinal cord injury pattern is central cord syndrome. Central gray matter destruction with sparing of the peripheral sacral spinothalamic and corticospinal tracts causes the characteristic findings of greater motor deficits in the upper extremities than in the lower extremities. Central cord syndrome usually occurs in elderly patients with underlying cervical spondylosis who sustain a hyperextension injury during a fall. Most patients present as quadraplegics with perianal sensation. Patients first regain bowel and bladder function followed by motor function. Motor function recovers in a caudal to cranial fashion with sacral motor elements returning first followed by lumbar motor elements. Recovery of upper extremity function is usually minimal and depends on the degree of central gray matter destruction. Functional recovery in central cord syndrome is moderate, with 75% achieving independent ambulatory status and bowel and bladder function.²⁹

Anterior cord syndrome occurs with injury to the anterior two thirds of the spinal column, causing complete loss of motor and sensory function below the level of injury. Patients often retain pressure sense and proprioception of the lower extremities since the dorsal spinal tracts are spared.³⁰ This syndrome has the worst prognosis for functional recovery, with only 10% of patients regaining ambulatory status.³¹

Posterior cord syndrome involves loss of proprioception and vibrational sensation. This rare syndrome involves injury to the dorsal spinal columns with relative preservation of anterior and lateral column function. Patients have difficulty coordinating movement but maintain motor power, pain, and temperature sensation.³²

Brown-Séquard syndrome results from hemisection of the spinal cord from penetrating injuries such as knife and gunshot wounds. This hemisection causes an ipsilateral motor deficit in combination with contralateral loss of pain and temperature sensation. Patients sustain ipsilateral motor loss because motor fibers in the corticospinal tract run ipsilaterally after decussating in the lower medulla. Brown-Séquard syndrome has the best prognosis, with almost all patients regaining bowel and bladder function and the ability to ambulate.^33,34

Mechanisms of Cervical Spine Trauma

Mechanisms of cervical spine injury include flexion, extension, axial loading, and rotation. Most injuries occur from rapid head deceleration or indirectly as the result of a blow to the cranium. Fracture patterns depend on the vertebral alignment at the time of injury and the direction of force. A description of the mechanism of injury is based on the magnitude and direction of the forces applied to the head and neck.³⁴ Most injuries are the result of a complex combination of forces.³⁵

Imaging Studies

Radiographic films for evaluating cervical spine injuries include anteroposterior, lateral, and open mouth odontoid views to visualize from the occiput to the first thoracic vertebra. Visualization of the cervicothoracic junction is critical because fractures of C7 and dislocations at the C7-T1 junction account for almost 17% of all injuries.³⁶ Noncontiguous spinal column injuries occur in 10% to 15% of patients; subtle findings such as soft tissue swelling, disc space narrowing or widening, and abnormal interspinous distances may indicate additional injuries.³⁷

CT use is increasingly popular because it provides superior bony anatomy resolution and excellent visualization in regions of the cervical spine that are difficult to assess with plain radiographs, such as the cervicothoracic junction. Fractures of the posterior elements are common; CT scans can easily identify fractures of the pedicle, facet joints, and lamina. The presence of these fractures may influence surgical management. The widespread availability of CT and its superior resolution of bony anatomy have led some radiologists to suggest CT before or in lieu of plain radiographs.³⁸ The medicolegal and economic implications of using CT scans to evaluate and identify cervical spine injuries, however, are considerable and its use remains controversial.^39,40

MRI is a valuable tool that can reveal injuries to the intervertebral disc, posterior ligament complex, and vertebral arteries. From 10% to 40% of patients with bilateral facet dislocations have associated disc herniations.^41–43 Fortunately, disc herniations with significant cord compression are infrequent and most herniations are clinically insignificant. It is now recognized that much of the stability of the cervical spine is conferred by the posterior ligamentous complex. The ability to detect subtle soft tissue injuries of the posterior capsuloligamentous structures makes MRI an invaluable tool in evaluating and guiding treatment of cervical spine injuries.⁴⁴ Vertebral artery injuries occur frequently in cervical spine fractures, with reports as high as 44% in traumatic subluxations.⁴⁵ Although optimal management of vertebral artery injuries remains controversial, MRI and CT angiography are becoming popular methods of evaluating for these injuries in the setting of subaxial cervical trauma.⁴⁶

Classification of Cervical Spine Injuries

Numerous systems have been proposed to classify cervical spine fractures. Classification systems have been based on morphologic features, mechanism of injury, and degree of instability. An ideal classification system is descriptive, provides insight to the clinical scenario, has prognostic value, and helps direct clinical treatment. Despite the numerous classification systems, none have been universally accepted or clinically validated.

Sir Frank Holdsworth developed the first comprehensive classification system for the spinal column, based on his experience with more than 2000 spinal column injuries. Fractures were categorized based on radiographic appearance. Injuries were described as wedge fractures, shear fractures, burst injuries, extension injuries, dislocations, or rotational fracture-dislocations. Although this system did not differentiate between cervical and thoracolumbar injuries, Holdsworth was the first to recognize the importance of the posterior ligamentous complex.⁴⁷

The most widely used classification system was proposed by Allen and Ferguson in 1982. Their mechanistic system was developed from a review of 165 patients. Fractures were classified based on static radiograph appearance and documented mechanisms of injury. Six phylogenies were identified based on the position of the cervical spine at the moment of injury and the principle mechanism of load to failure. The categories proposed by the authors were distractive extension, compressive extension, lateral flexion, vertical compression, compressive flexion, and distractive flexion. Each category was further staged based on the severity of the anatomic disruption. Allen and Ferguson placed bilateral facet dislocations in the distraction flexion phylogeny.⁴⁸

Moore’s Cervical Spine Injury Severity Score evaluates the four columns of the cervical spine to assess stability.⁴⁹ The four-column model is a modification of the three-column model proposed by Louis⁵⁰ and includes the anterior column, right pillar, left pillar, and the posterior osseous ligamentous complex. Injury to each of the four columns is assessed on plain radiographs and CT scans and is assigned a score based on the degree of bony displacement and ligamentous disruption (Fig. 226-2). The sum of these four scores is used to determine stability, with higher scores signifying more unstable injuries.

FIGURE 226-2 A, Moore’s Cervical Spine Injury Severity Score is based on a four-column analysis of the cervical spine. B, Injury to each column is scored on the basis of both bony displacement and ligamentous disruption.

(Adapted from Moore TA, Vaccaro AR, Anderson PA: Classification of lower cervical spine injuries. Spine [Phila Pa 1976] 31:S39, 2006.)

The Subaxial Injury Classification scoring system (SLIC) was developed to guide clinical treatment. This system incorporates the injury morphology, integrity of the discoligamentous complex (DLC), and the patient’s neurologic status into the scoring. Injury morphology is divided into three main categories. The morphologic categories of compression, distraction, and rotation/translation are assigned points according to injury severity. The anatomic components of the DLC, including the intervertebral disc, anterior and posterior longitudinal ligaments, ligamentum flavum, interspinous and supraspinous ligaments, and the facet capsules, are evaluated on radiography, CT, or MRI. Points are given to any potential or definitive DLC injuries. Neurologic status is a key component to the SLIC system; point values are assigned for root injuries, cord injuries, and continuous cord compression with a neurologic deficit. If the total score in the three categories is between 1 and 3, then the injury can be managed nonoperatively. The authors recommend operative treatment for injuries with scores greater than or equal to 5⁵¹ (Table 226-2).

TABLE 226-2 Subaxial Injury Classification Scoring System

Total score derived from three main components: injury morphology, integrity of the discoligamentous complex, and the neurologic status.

Adapted from Vaccaro AR, Hulbert RJ, Patel AA, et al: The Subaxial Cervical Spine Injury Classification system: a novel approach to recognize the importance of morphology, neurology, and integrity of the disco-ligamentous complex. Spine (Phila Pa 1976) 32:2367, 2007.

Bilateral Facet Dislocations

Facet dislocation and fracture-dislocations represent a spectrum of osteoligamentous injury. Allen and Ferguson placed these injuries in the distraction flexion phylogeny of their classification system. Facet subluxations are classified as stage I injuries and unilateral facet dislocations are classified as stage II injuries. Anterior translation of the vertebra indicates a bilateral facet dislocation. Injuries with 50% anterior vertebral translation are stage III injuries; injuries with complete dislocation are classified as stage IV⁴⁸ (Fig. 226-3).

FIGURE 226-3 Allen and Ferguson classification of distractive-flexion injuries. A, Normal; B, stage 1; C, stage 2; D, stage 3; E, stage 4.

(Adapted from Klein GR, Vaccaro AR: Cervical spine trauma: upper and lower. In Vaccaro AR, Betz RR, Zeidman SM, editors: Principles and practice of spine surgery, Philadelphia, 2003, Mosby, p 456.)

Pathomechanics of Bilateral Facet Dislocation

The dynamics of cervical spine injuries are extraordinarily complex.^52,53 Bilateral facet dislocations are most often caused by hyperflexion in combination with some rotation^35,54 (Fig. 226-4). These injuries are frequently the result of motor vehicle accidents, falls, or head-first dives into shallow water.⁷ Flexion is resisted by the posterior structures, including the supraspinous and interspinous ligaments, the ligamentum flavum, and the facet capsules. Hyperflexion injuries occur when the head is flexed beyond the physiologic limits of the cervical bone and ligamentous complex. The distraction force during hyperflexion creates tension in the posterior structures and causes rupture to occur in a posterior to anterior direction. Cadaveric dissections of bilateral facet dislocations show significant injury to all the posterior ligamentous components, including the ligamentum flavum, facet capsules, and disc anulus. Often the only remaining intact structure is the anterior longitudinal ligament.^54,55 Injuries to the anulus are of particular importance because the nucleus pulposus and portions of the anulus can retropulse into the spinal canal and compress the spinal cord and neural elements.^41–43

FIGURE 226-4 A and B, Bilateral injuries occur with forces that are predominantly that of flexion.

(Adapted from Mirza SK, Anderson PA: Injuries of the lower cervical spine. In Browner BD, Jupiter JB, Levine AM, Trafton PG, editors: Skeletal trauma, ed 3, Philadelphia, 2003, Saunders, p 837.)

Management of Bilateral Facet Dislocations

Treatment of patients with potential spine trauma begins before arrival at the hospital. The cervical spine is immediately placed in a collar and the patient evaluated with Advanced Trauma Life Support protocol.⁶⁰ The patient should be moved and transported on a rigid spine board. A detailed history of the injury events can provide valuable insight on the energy level and mechanism of injury. During the primary survey, the ABCs of basic life support are assessed and a thorough physical examination is performed.⁶¹ A detailed neurologic examination will reveal any neurologic deficits. Careful attention to hemodynamic status may reveal neurogenic shock. Neurogenic shock is vascular hypotension with bradycardia caused by traumatic disruption of sympathetic outflow and unopposed vagal tone.^61,62 Hypotensive, bradycardic patients who do not respond to fluid resuscitation have neurogenic shock and should be treated with vasopressive agents such as epinephrine. Evaluation of the cervical spine begins with removal of the collar and palpation of the posterior neck. Any midline or paraspinal tenderness may indicate a cervical injury.^4,63 The relative position of the head and neck should be noted; any angular or rotational deformities may suggest a unilateral dislocation. The remainder of the axial spine can be palpated after logrolling the patient.