12.40 Subaxial cervical spine injuries

Approximately 150 000 spinal injuries present to the Emergency Rooms of the United States of America every year, and roughly, 7.5% of these present with a neurological injury. Improvements in on-site resuscitation and in the delivery of emergency medical care have significantly improved the survival of patients with spinal cord injuries. Multiple classification systems have been proposed to describe the different injury patterns, and the principles laid out by Allen and Ferguson, where injuries are classified according to the mechanism of failure, continue to be valid and widely accepted.

The interpretation of clinical findings and imaging studies to identify different injury patterns constitutes the first part of a successful treatment plan. Injury patterns reflect the biomechanics, the direction and severity of trauma, and the degree of instability of the cervical spine. The classification system adopted by the Spine Trauma Study Group describes three families of injuries according to the relationship of the vertebral bodies with one another: compression, distraction, and translation/rotation. Additionally, the presence of neurological injury and the integrity of the discoligamentous structures (intervertebral disc, anterior and posterior longitudinal ligaments, supra- and interspinous ligaments, facet joint capsules, and ligamentum flavum) constitute important indicators of the severity of the injury.

Management of cervical spine injuries starts at the site of the accident, following initial resuscitation guidelines described by the American College of Surgeons and includes protection of the spine and spinal cord during the primary survey. From the initial extrication and on-site management, it should be assumed that all trauma patients have a cervical spine injury until otherwise proven.

Patients with altered mental status or those presenting with distracting injuries are at a particular risk. Some authors have estimated that 3–25% of spinal cord injuries occur during extrication, acute resuscitation, and transport. For this reason, a rigid cervical orthosis must be used at all times, until the cervical spine has been formally cleared, which requires a reasonable certainty that the patient’s cervical spine is stable and free of significant injury. On the other hand, excessive use of a cervical orthosis can be associated with complications, including aspiration pneumonia, mandibular and occipital ulcers, limitations of respiratory function, and even possible increases in intra-cranial pressure. The protocol used in our institution for clearance of the cervical spine is described in Figure 12.40.1, and is further detailed as follows:

An awake and alert patient is better able to cooperate with the clinical examination than an obtunded or unconscious patient. Also, the presence of other injuries, such as chest or abdominal trauma, or other musculoskeletal conditions, can distract from the symptoms of a cervical spine injury.

Clinical examination is sufficient to rule out a traumatic injury to the cervical spine in patients that present alert and awake, and have no complaints of neck pain or neurological deficit. The patient should be able to rotate the neck at least 45 degrees in each direction and have a normal neurological examination. This practice guideline is supported by Class I data, and has been extensively adopted in many institutions.

If the patient is awake and alert, and presents with neck pain or tenderness, there is a 2–6% chance of a significant cervical spine injury that will require specific treatment. In this scenario, clinical examination alone has a negative predictive value of 96.7%, but a sensitivity of only 66.7%. For this reason, radiographic examination is mandatory. Similarly, imaging studies are also mandatory for all patients who present with altered mental status, neurological injury, or other distracting injuries.

The basic trauma cervical spine series includes anterioposterior (AP) and lateral radiographic views, as well as an open-mouth odontoid view. Cervical spine radiographic series alone are associated with 15–17% false negatives. Because most of the misdiagnosed injuries are located in the occipitocervical or in the cervicothoracic junction, the addition of computed tomography (CT) scan increases the negative predictive value to 99.7% by improving the visualization of these areas. Despite the absence of osseous injury, instability can exist as a consequence of disruption of the spinal ligaments and other soft tissue components of the motion segment. These purely ligamentous injuries are of rare occurrence (0.1–0.7%). Flexion–extension radiographs can be safely used to rule out instability when the basic trauma cervical spine series is normal, only if the patient is awake and cooperative. Nevertheless, fluoroscopy and passive flexion–extension radiographs present risk of iatrogenic spinal cord injuries in obtunded and non-cooperative patients. Dynamic fluoroscopic examination is only able to detect surgically relevant injuries in 0.56% of patients not detected by CT scan. Finally, magnetic resonance imaging (MRI) is not recommended as a screening tool, but may provide important information when planning treatment. In a recent study, MRI showed abnormalities in 21.1% of patients with normal CT scan and normal neurological examination, nevertheless, any of these injuries required additional treatment.

Obtunded and uncooperative patients are temporarily radiographically cleared following review of cervical spine trauma series and CT. Particularly if the patient presents with high risk criteria (motor vehicle collision >35mph (56km), fall from heights >10 feet (3m), closed head injury, neurological deficits referable to the cervical spine, and pelvis/extremity fractures) cervical spine precautions must include the permanent use of a cervical orthosis, until the patient is awake and cooperative and can than be clinically cleared (Figure 12.40.1).

Following diagnosis, specific treatment priorities are as follows:

Initial airway management and fluid resuscitation have a positive impact on spinal cord perfusion. Reduction with skeletal traction should be initiated as soon as possible, and if reduction cannot be achieved, or if there are other compressing elements on the spinal cord, surgical decompression and stabilization is recommended as soon as the patient’s condition has been optimized. The timing of surgery must be decided considering the characteristics of the injury, but also the general condition of the patient, and the local institutional and personnel. This continues to be a matter of controversy and significant research efforts. Animal models support acute decompression of the spinal cord, and there is an increasing body of clinical data to support this as well. Nevertheless, there is a lack of prospective trials to support early or acute intervention. Finally, the role of high-dose steroids is controversial and will not be discussed in this chapter.

If the spine is dislocated, or if there is significant impingement of the spinal cord by bone fragments, reduction with traction should be initiated on an emergent basis (Box 12.40.2). This procedure is safe if the patient is awake and cooperative. If neurological assessment is not reliable, as is the case of an obtunded or uncooperative patient, MRI is suggested prior to the onset of skeletal traction. The purpose is two-fold:

Reduction is achieved by applying direct axial skeletal traction with skull tongs or a halo-ring. After an initial application of 5–10kg (10–20 pounds), incremental additions of 5kg (10 pounds) are applied until reduction is confirmed. The patient should be awake but lightly sedated so as to reduce muscle contractures and facilitate reduction. The head can also be positioned so as to facilitate the reduction, usually with some flexion of the neck. After 20–30min in traction, the neurological status of the patient is monitored, and a lateral cross-table radiograph is obtained. If the spine is not reduced, additional weights are added, a neurological examination is performed, and a lateral cervical radiograph is obtained, as previously described. Our typical protocol includes adding weights up to approximately one-third of the body weight, if needed. At higher weights, tongs may displace, and a halo ring is preferable. Another advantage of a halo ring is that it may facilitate better control of the position of the head and neck relative to the axis of traction. Traction is contraindicated in ankylosed spines, such as those suffering from ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis (DISH).

Non-contiguous cervical spine injuries occur in up to 15% of the cases and must be assessed before traction is initiated. Monitoring of plain films during reduction should also include evaluation for overdistraction at the level of injury. MRI is indicated to rule out the presence of disc material occupying the spinal canal if new or progressive neurological symptoms develop during the procedure.

Indications for surgery will depend on stability of the spine and the need for neural decompression. Understanding the principles and definitions of stability is fundamental for adequate management decisions. White and Panjabi have defined stability as the ‘ability of the spine under physiologic loads to maintain its pattern of displacement so that there is no initial or additional neurological deficit, no major deformity and no incapacitating pain’. In the event of a traumatic injury, it must be recognized if these properties have been lost. For this purpose, these authors have also provided a checklist to guide the clinician in the determination of spinal instability, which is based on both clinical and radiological parameters. Unfortunately, there are no means to accurately determine instability. Injuries of the cervical spine represent a continuum, and in some cases, there may only be a very tenuous difference between indicating unnecessary surgery and avoiding a disastrous omission. Careful review of the points in this checklist will help guide clinical decisions. If the criteria provide for a particular injury to be considered unstable, surgery is indicated for the purpose of recovering stability. This is usually designed to counteract the disruptive forces that have acted upon the spine.

Radiolographic criteria are based on static and flexion-extension films (Figure 12.40.2). These criteria are based on biomechanical data obtained from serial sectioning of the ligamentous components of the spinal motion segment. These experiments showed that catastrophic failure could occur at physiological loads following sectioning of all posterior ligaments and one anterior ligament, or all anterior ligaments and one posterior structure. Furthermore, measurements made of intact motion segments showed a maximum displacement (measured between the posterior walls of adjacent vertebral bodies) of approximately 2.7mm and maximum angulation (measured between the inferior endplates of adjacent vertebrae) of 10.7mm. Only modest increases in displacement and angulation were observed before catastrophic failure occurred at physiological loads. The authors further suggested that to allow for variability in radiographic and measurement technique, measurements on a plain film lateral radiograph greater than 3.5mm of AP displacement or 11 degrees of angulation between adjacent vertebrae in excess of the angulation present in the levels above or below, imply potential instability in the clinical setting.

The number of cervical spine injuries without neurological impairment, or with incomplete spinal cord injuries arriving in emergency rooms, appears to be steadily increasing due to improved extrication and immobilization methods, on-site resuscitation, and improved trauma networks. The second most common reason for urgent surgery is in those patients with incomplete spinal cord injury with radiographic findings of ongoing spinal cord compression.

Three distinct categories of injury patterns are recognized based on the primary mechanism of injury: compression injuries, distraction injuries, and translation or rotation injuries.

Simple compression injuries are defined by failure of the anterior column (anterior half of the vertebral body), with sparing of the posterior cortex of the vertebral body. They are usually not related to any form of neurological injury, and may be treated by the use of a cervical orthosis for 8–12 weeks. Early in the course of treatment, and as soon as the patient has developed reasonable comfort, flexion and extension films are taken to asses for patterns of instability. Additionally, serial radiographs are recommended to monitor for the potential development of progressive deformity (kyphosis).

Burst fractures are those where the structure of the vertebral body has failed under compressive loads, extending through the posterior cortex. As the energy dissipates into the vertebral body, bony fragments are ejected in all directions, including retropulsion of bone fragments into the spinal canal, frequently involving the spinal cord. Surgical decompression is indicated for ongoing spinal cord compression and is achieved by means of a corpectomy. Stability is achieved by the interposition of a strut graft and anterior locking plate.

Distraction injuries may occur with an extension or with a flexion moment. Hyperextension injuries are most likely to occur in a rigid, spondylotic spine. The energy is dissipated through anterior osteophytes, vertebral body, and into the posterior ligaments and facet joints. Hyperflexion injuries damage the posterior tension band, including the supra- and interspinous ligament complex, ligamentum flavum, and facet joint capsules, resulting in facet subluxation or perched facets. Varying degrees of damage to the posterior longitudinal ligament and posterior annulus also occur.

Ideally, reduction of uni- or bilateral perched facets should be obtained by skeletal traction with an awake and cooperative patient. If this fails, then surgical reduction and stabilization is considered. This can be achieved from either anterior or posterior approaches. We recommend a preoperative MRI in these cases. If there is evidence of extruded disc material, posterior to the body of the inferior vertebra, an anterior approach is recommended. This will allow for anterior decompression of the spinal canal, reduction of the dislocated facet joints and stabilization by means of an interbody graft and an anterior locking plate. If there is no evidence of disc extrusion, a posterior approach is preferred, as it provides for easier reduction of the dislocated facet joints. Although posterior fusion with lateral mass screw fixation provides superior biomechanical characteristics, progressive kyphosis is likely to develop, particularly in cases where the inter-vertebral disc has been disrupted.

Hyperextension injuries commonly occur in previously spondylotic spines with varying degrees of ankylosis (see Figure 12.40.2). These injuries are increasingly common in our increasingly active aging population. The spinal canal is commonly stenotic (Torg’s ratio <0.8), and the mechanism of hyperextension results in a pincer phenomenon, compressing on the spinal cord, between the posteroinferior margin of the superior vertebra, and the anterosuperior border of the lamina from the inferior vertebra. This will result in spinal cord ischemia, frequently manifest as central cord syndrome. Furthermore, if the spine is extensively ankylosed, a significant lever arm is formed over the fracture site, resulting in a highly unstable injury pattern. An increased retropharyngeal soft tissue shadow, a widened disc space with high-signal intensity on T₂-weighed MRI (otherwise degenerative disc spaces present with low-signal on T₂), anterior osteophyte avulsion or avulsion injury of the anteroinferior vertebral body should be warning signs of this highly unstable injury.

These patients commonly present with persistent cord compression, which may or may not be accompanied by bone or disc-ligament injury. If the spine is stable and the neurological status is static or improving, initial non-surgical treatment with close follow-up is recommended. Delayed or late decompression may be required if symptom improvement is stagnant. Alternatively, some authors advocate early surgical decompression.

If surgery is indicated for spinal cord decompression and the spine is considered stable, then the approach will be determined by the alignment of the cervical spine, and the number of affected levels. A posterior approach with a laminoplasty is recommended for a lordotic spine with multiple levels of compression. If the spine is neutrally aligned or slightly kyphotic, and if lordosis is obtainable on extension films, the same approach is accompanied by laminectomy and fusion with lateral mass screw fixation. Conversely, if the spine is focally kyphotic, and if the main compressive element is an anterior disc-osteophyte complex, then anterior surgical decompression and fusion is recommended.

Fractures through a previously ankylosed cervical spine require special attention. This may occur in ankylosing spondylitis, DISH (or Forestier’s disease), or in extensive multilevel cervical spondylosis. The injured motion segment is extensively ossified, including most, if not all of the spinal ligaments, facet joint capsules, and even the inter-vertebral disc (ankylosing spondylitis). As a consequence of this, the fracture through the ankylosed motion segment will compromise all of the stabilizing structures, rendering significant instability, similar to a long-bone fracture, with long lever arms acting on the injury and the spinal cord.

These injuries frequently occur in elderly, osteoporotic patients, and result from low-energy trauma. They are frequently missed, and initial diagnosis is based on a high level of clinical suspicion. Once recognized, these injuries must be immediately immobilized, and treated as highly unstable. The patient depicted in Figure 12.40.3A presented with neck pain after a fall at home, and the lateral film shows a fracture line through an extensively ankylosed spine secondary to DISH. He was immediately placed on cervical orthosis, and taken to MRI for further evaluation (Figure 12.40.3B), where the injury was recognized to be displaced. The patient was indicated for emergent surgical fixation. Skeletal traction must be avoided, as it only contributes to further displacement. Surgical treatment, in the form of a multisegment posterior instrumentation is recommended to provide stability to the long lever-arms and poor bone quality. Postoperative immobilization is mandatory, and should be maintained until the injury and fusion have completely healed.

These injuries are recognized by the presence of translation of one vertebra relative to the adjacent one. Translation can occur in the sagittal plane, coronal plane, rotational plane, or combined. In bilateral facet dislocation, the mechanism is of pure anterior translation, whereas in unilateral facet fracture or dislocation, the mechanism is that of rotational translation with a fulcrum around the intact facet joint. Translation can occur as a product of disruption of disc-ligament structures or fracture of the articular process. There is a wide spectrum of injuries ranging from unilateral or bilateral dislocated facets, to the fracture-separation of the articular process, where the dissociation of the articular process (Figure 12.40.4) from the vertebral body and lamina affects the relationship to both the superior as well as to the inferior motion segments. In general, the more elements that are compromised with the injury, the easier it is to obtain closed reduction. Unilateral facet dislocation, are the most difficult injuries to reduce.

Facet fractures and dislocations are easily recognized on plain films. In unilateral dislocation, the AP film will reveal a loss of colinearity of the spinous processes at the level of the injury. The lateral films will add varying degrees of vertebral body translation. If this listhesis is 25% of the AP diameter of the vertebral body or less, unilateral facet joint fracture or dislocation is the rule (Figure 12.40.5), whereas with a listhesis of 50% or more is commonly associated with bilateral dislocations (Figure 12.40.4). Unilateral facet fractures or dislocations usually present with radiculopathy secondary to foraminal stenosis, whereas bilateral facet fractures or dislocations frequently present with spinal cord injury.

Management consists of emergent reduction with the use of skeletal traction, following the previously described protocol. Approximately 25–50% of patients will fail close reduction and will require open reduction under general anesthesia. Once reduction is achieved, surgical stabilization is mandatory, and may be obtained by either anterior or posterior instrumented fusion. Prior to open reduction, we recommend an MRI to identify the presence of extruded disc material posterior to the body of the inferior vertebra. In such a case, an anterior approach is recommended. This will allow for anterior decompression of the spinal canal, reduction of the dislocated facet joints, and stabilization by means of an interbody graft and an anterior locking plate. If there is no evidence of disc extrusion, a posterior approach is preferred, as it provides for easier reduction of the dislocated facet joints. Posterior instrumentation with lateral mass screw fixation provides superior biomechanical characteristics when compared to anterior plate fixation and interbody graft. Nevertheless, in cases where the intervertebral disc has been disrupted, progressive kyphosis may develop. Furthermore, posterior fusion requires a more traumatic dissection and prone positioning, both of which are avoided in anterior fixation. Anterior fixation provides direct decompression, has similarly high fusion rates, and compares favorably in the restoration and maintenance of segmental lordosis. Nevertheless, if a fracture of the superior endplate of the vertebral body is associated with the translational deformity, anterior fixation alone is insufficient with early mechanical failure in two-thirds of the cases. In this situation, combined anterior and posterior fixation is recommended, similarly to injuries with significant posterior ligament complex disruption, such as the case of teardrop fracture-dislocations.

The teardrop fracture is an injury pattern that results from axial loading and forced flexion of the cervical spine (Figure 12.40.2). This is common in injuries occurring when diving in shallow waters. It has also been termed burst fracture dislocation. A characteristic T-shaped fracture through the superior endplate of the vertebral body (Figure 12.40.2A) is associated with varying degrees of facet and articular process fracture as well as severe disc-ligament injury, affecting the facet joints, intervertebral disc, anterior and posterior longitudinal ligaments, and the ligamentum flavum (Figure 12.40.2B). The superior vertebra is not only is axially loaded against the inferior vertebra, but also rotates over its axis, thus indenting its anteroinferior margin into the superior endplate of the inferior vertebra. This further displaces the posterior aspect of the vertebral body into the spinal canal, through a sagittal fracture line. The key feature is the displacement of the posterior vertebral body fragments into the spinal canal, both relative to the superior, as well as the inferior adjacent vertebral bodies. This finding must be recognized because it reflects a severe degree of discoligamentous complex injury, which results in continuous cord compression, as well as severe instability. Complete spinal cord injury is frequently present, and the recommended treatment includes decompression of the spinal canal through a corpectomy, and reconstruction with combined anterior and posterior instrumentation. Reduction by traction is rarely indicated, as the degree of disruption of the discoligamentous complex easily leads to overdistraction of the spinal canal and spinal cord.