Anatomy

The subaxial cervical spine consists of the C3-7 vertebrae. The cervical spinal canal houses the spinal cord and is bound by the vertebral body anteriorly, pedicles laterally, and the laminae posteriorly. The transverse process, which is directed anterolaterally, contains the transverse foramen. The vertebral artery enters the transverse foramen at C6 in 90% of the population and travels up the subaxial cervical spine. Off of the lamina, the inferior and superior articular processes form the facet joints, which are oriented at 45 degrees. The uncovertebral joints are formed by a bony protuberance, known as the uncinate process, on the lateral aspect of the superior vertebral body, which articulates with a convex area in the lateral aspect of the inferior vertebral body. The intervertebral disc is found in the intervertebral disc space and is composed of the gelatinous nucleus pulposus centrally and the fibrocartilaginous annulus fibrosus peripherally. The uncovertebral joint protrudes through an area absent of annulus fibrosus and is believed to be lined by a synovial membrane. The spinous processes project posteriorly and are bifid between C3 and C6. Ligamentous structure is provided on the anterior and posterior aspects of the vertebral bodies by the anterior longitudinal ligament (ALL) and the posterior longitudinal ligament (PLL), respectively. The ligamentum flavum is found connecting adjacent lamina and facet capsules. The interspinous and supraspinous ligaments provide further support between the spinous processes posteriorly.

As Bogduk and Mercer noted, the principal movements of the subaxial spine are flexion and extension. This is facilitated by the observation that cervical vertebral bodies are not stacked flatly upon one another but are situated with a sagittal slope. The bony and ligamentous anatomy as well as the intervertebral discs together limit excessive motion of the cervical spine. This prevents injury to the cervical spinal cord while allowing functional motion. The PLL, the facet capsules, the ligamentum flavum, and the interspinous ligaments all resist flexion. Extension is limited by ALL and the annulus fibrosus, as well as the posterior bony anatomy. Excessive movement in these planes of motion can result in injury to these structures.

The cervicothoracic junction is of particular interest due to its transitional and variable anatomy. The potential presence of the vertebral artery, tenuous blood supply, and narrow spinal canal make screw placement in this segment difficult and controversial. The cervical vertebrae enlarge moving caudally and are slightly lordotic ending at the cervicothoracic junction where the alignment becomes kyphotic in the thoracic spine. When this transition of curvature occurs, a transition of weight distribution occurs as well complicating intervention. For screw placement, three techniques have been advocated and criticized, including pedicle, laminar, and lateral mass screws. Compared to thoracic pedicles, cervical pedicles are smaller with an increase in height and width and a decrease in angle with the vertebral body moving caudally toward the thoracic spine. Placement of a pedicle screw risks neurovascular compromise with transverse foramen involvement. Translaminar screw use presents the possibility for penetration into the dorsal spinal canal. At C7 the lateral mass is thin and small compared to higher cervical vertebrae presenting screw pullout as a common complication.

Clinical Assessment

In the immediate aftermath of an acute spinal cord injury (SCI), patients frequently develop neurologic dysfunction. These neurologic problems are likely to manifest with functional deficits, and patients often experience pain. The best medical evidence suggests that patients who experience spinal cord injury should undergo serial evaluation and documentation of neurologic and functional deficits, as well as pain severity.

Many classification systems have been developed to document and standardize neurologic evaluation of the patient with acute spinal cord injury. These include the Frankel Scale, the Lucas and Ducker Neurotrauma Motor Index, the Sunnybrook, the Botsford, the Yale scale and the National Acute Spinal Cord Injury scales, among others. The ideal scale would have inter-rater reliability, reproducibility, sensitivity to changes in neurologic function, and would provide accurate documentation. The scale would then be sufficiently useful for management and research purposes. Currently, the American Spinal Injury Association (ASIA) scale best meets these criteria and is the preferred neurologic examination tool, as shown in Figure 128-1 .

American Spinal Injury Association (ASIA) neurologic classification form used to document the physical examination of a patient after cervical trauma.

This classification system is as follows:

• 
  

  A = Complete. No sensory or motor function is preserved in the sacral segments S4-5.

  
  
• 
  

  B = Sensory incomplete. Sensory but not motor function is preserved below the neurologic level and includes the sacral segments S4-5, and no motor function is preserved more than three levels below the motor level on either side of the body.

  
  
• 
  

  C = Motor incomplete. Motor function is preserved below the neurologic level, and more than half of key muscle functions below the single neurologic level of injury have a muscle grade less than 3 (grades 0 to 2).

  
  
• 
  

  D = Motor incomplete. Motor function is preserved below the neurologic level, and at least half (half or more) of key muscle functions below the neurologic level of injury (NLI) have a muscle grade > 3.

  
  
• 
  

  E = Normal. If sensation and motor function as tested with the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) are graded as normal in all segments, and the patient had prior deficits, then the ASIA Impairment Scale (AIS) grade is E.

The procedure for determining the ASIA grade is outlined in the ISNCSCI. Briefly, the neurologic examination tests two components: sensory and motor. The sensory examination tests light touch and pin prick sensation at 28 points, corresponding to separate dermatomes on the right and left side of the body. The motor examination consists of testing 10 paired myotomes graded with the standard six-point scale. An NLI is then determined for the most caudal aspect of the right and left side, with antigravity motor function and intact sensation. From these four possible NLI, the single NLI is the most rostral and is used in the ASIA classification process.

Burns and coworkers noted decreased reliability of the initial examination in the presence of closed head injury, drug effects, mechanical ventilation, and psychologic disorders. It has also been suggested that impairment following SCI can be better described and predicted with separate upper and lower extremity ASIA motor scores.

Although ASIA was designed to measure neurologic deficits, it does not take into account spasticity, pain, or dysesthesias; therefore, a number of scales have been developed to assess for functional deficits. These scales attempt to document the patient’s deficiencies in daily functioning. These include the Functional Independence Measure Scale, the Barthel Index, the Quadriplegic Index of Function, and the Spinal Cord Independence Measure (SCIM), among others. Currently, the third revision of the SCIM scale, SCIM III, is recommended for functional assessment in patients with acute spinal cord injury. This scale was specifically designed for patients with spinal cord injury, in that it derives from assessment of one’s ability to perform basic tasks, economic burden of disability, and impact on overall comfort. Additionally, SCIM III provides documentation, which is sensitive to functional changes, has inter-rater reliability, and is reproducible, making it useful for patient care as well as research purposes.

SCIM III consists of three complementary subscales: “self-care” (with a score range of 0 to 20) including six tasks, “respiration and sphincter management” (with a score range of 0 to 40) including four tasks, and “mobility” (with a score range of 0 to 40) including nine tasks. The mobility subscale consists of two subscales: one for “room and toilet” and the one for “indoors and outdoors, on even surface.” Total score ranges between 0 and 100.

Pain is also a common complication after spinal cord injury and can be severely debilitating. Consequently, numerous methods have been developed to measure the pain in both objective and subjective ways. Ideally, these scales would provide a method to document pain following spinal cord injury and allow assessment of the efficacy of treatment. The most highly recommended of these to date is the International Spinal Cord Injury Basic Pain Data Set (ISCIBPDS).

Radiographic Assessment

In patients who present with potential cervical spinal injury, the necessity of imaging must first be determined. A number of criteria have been developed to make this. If imaging is indicated, computed tomography (CT) scanning has been shown to be most effective, though plain films, dynamic films, and magnetic resonance imaging (MRI) may have a role.

The National Emergency X-Radiography Utilization Study Group uses five criteria to determine whether or not patients with potential cervical spine injury require imaging. If all of the five criteria are present, patients require no imaging. These criteria include absence of midline cervical tenderness, absence of focal neurologic deficit, normal alertness, absence of intoxication, and absence of painful, distracting injury. The Canadian C-spine uses three criteria to determine if a patient requires imaging. These include presence of a high-risk factor that mandates radiography, presence of a low-risk factor allowing safe assessment of range of motion, and ability to actively rotate neck 45 degrees to the left and right. Anderson and colleagues found that patients who are alert, asymptomatic, and without neurologic deficit who can complete a functional range of motion examination and are free from other major distracting injury can be released from cervical immobilization without radiographic imaging. The sensitivity of each of these methods for spinal cord injury is high, though best medical evidence supports the use of the criteria of Anderson and colleagues.

For patients who require imaging, CT is more sensitive than three-view cervical plain films for detecting cervical spine injury. The sensitivity of plain films for diagnosing cervical spine injury is thought to be between 35% to 53%, whereas CT can approach 100%. If CT is unavailable, three-view cervical plain films can be used, though they are not preferred. In symptomatic or obtunded patients with negative CT or plain radiographs, investigators have studied the utility of MRI and flexion/extension radiographs to further assess for cervical spine injury and determine the need for continued cervical immobilization. Controversy exists in regard to the utility of both. Studies have investigated the usefulness of MRI in these patients and have found it helpful, but others have not. More work is needed to determine which patients can benefit from an MRI. Dynamic films are thought to be less sensitive for ligamentous injury than MRI and to be of little use in the setting of a normal CT scan and clinical examination. There are also reports of injury to obtunded patients undergoing dynamic imaging, which raises questions as to the safety of the procedure in these patients.

Injury Classification

Many systems have been proposed to classify injuries from C3-7 in the setting of trauma; a more commonly used system by Magerl and associates had originally been designed for use in the thoracolumbar spine. In 2007, publication of the Subaxial Injury and Classification (SLIC) and severity scale by the Spine Trauma Study Group posed a more focused and clinically oriented guideline for management of subaxial cervical spine injuries. Since the publication of SLIC, more recent classification systems have been proposed, but additional literature is needed for their validation.

The three parameters evaluated in the SLIC classification are injury morphology, spinal stability, and neurologic status ( Fig. 128-2 ). According to the SLIC grading system, injury morphology is classified as (0) no abnormality, (1) compression fracture, (2) burst fracture, (3) distraction injury, and (4) translation injury. The SLIC scoring system grades discoligamentous complex (DCL) integrity as (0) intact, (1) indeterminate, and (2) disrupted. Finally, neurologic status is defined as (0) intact, (1) nerve root injury, (2) complete spinal cord injury (SCI), (3) incomplete SCI, and (+1) persistent cord compression. Patients with a total score of 1 to 3 are recommended to be treated conservatively with a PMT collar. It is recommended that patients with a score of 4 are treated either operatively or nonoperatively based on the patient and surgeon. For example, a patient with a SLIC score of 4 with significant comorbidities may respectably be managed nonoperatively. Lastly, patients with a score of 5 or more are highly recommended for surgical decompression or stabilization.

Distribution of lower cervical spine injuries among 165 patients. CE, compressive extension; CF, compressive flexion; DE, distractive extension; DF, distractive flexion; LF, lateral flexion; VC, vertical compression.

(Data from Allen BL, Ferguson RL, Lehmann TR, et al: A mechanistic classification of closed indirect fractures and dislocations of the lower cervical spine. Spine [Phila Pa 1976] 7:1–27, 1982.)

Studies evaluating the SLIC scoring system demonstrate strong inter- and intraobserver agreement (> 90%) in both the overall injury score and treatment plan chosen. These authors also evaluated the validity of SLIC by performing a retrospective review of 185 patients comparing their management to the recommendations of the SLIC guidelines. Of the 66 patients with a SLIC score of 3 or less, 94% of them were managed nonoperatively; of the 102 patients with a SLIC score of 5 or greater, 95% of them were managed surgically. Of the 17 that had a SLIC score of 4, 65% were conservatively managed. A prospective study also supports the SLIC guidelines as effective in preserving neurologic status after subaxial cervical spine trauma. Despite evidence and support from proponents of the SLIC system, the guidelines do have certain drawbacks, therefore controversy for their use still exists.

One such parameter is evaluating and elaborating upon the morphology of cervical spine injuries. According to SLIC, no abnormality (0) includes isolated spinous process fractures, laminar fractures, or nondisplaced facet or pedicle fractures. A floating lateral mass without significant displacement, for example, would be difficult to classify. Compression fractures (1) are represented as simple anterior compression, comminuted fractures, or the more severe teardrop fractures, the latter of which is highly associated with spinal instability injury. Distraction (3) injuries primarily involve the intervertebral disc and ligamentous structures with anatomic dislocation in the vertical axis. Trauma associated with hyperflexion often results in compression of the anterior column and a distraction injury of the posterior column; trauma associated with hyperextension will have distraction of the anterior column. Often, a component of both are involved in level I traumas. Of note, distraction injuries can also present as injured facets, which may or may not be reliably reflected by the SLIC guidelines. This may be a contributing factor in delayed glacial instability following facet fractures. Lastly, with translational injuries (4), rotation is typically the dominant force. This can present as unilateral or bilateral facet joint or fracture dislocations. Invariably so, both distraction and translational injuries pose a threat to spinal stability.

Special attention should be warranted in patients with previous cervical spondylosis. For example, a patient suffering from a complete spinal cord injury secondary to hyperextension in the setting of cervical spondylosis could be scored a 3 on the SLIC scale, with (0) normal morphology, (0) intact DCL, and (2) complete, (+1) persistent cord injury; but these patients may benefit from surgical decompression.

Spinal Stability

Spinal stability is assessed primarily by the overall alignment of the spine and the integrity of the discoligamentous complex (DLC). The DLC comprises the intervertebral disc, anterior and posterior longitudinal ligaments, interspinous ligaments, facet capsules, and ligamentum flavum. Again, the SLIC scoring system grades DLC integrity as (0) intact, (1) indeterminate, and (2) disrupted. Although spinal alignment is a reflection of ligamentous stability, isolated bony injuries can result in significant spinal instability with an intact DLC such as in the case of a three-column bony chance type fracture.

In the majority of circumstances, disrupted DLC is established by evidence of distraction or translation to the spinal column or significant disruption of the intervertebral disc space or facet joints. Isolated injuries to the ALL, PLL, ligamentum flavum, or interspinous ligaments may not truly represent disruption of the DLC. Identifying and scoring the DLC as indeterminately injured is controversial in this setting and because MRI tends to overestimate true ligamentous injury. An MRI, however, should be considered to assess the intervertebral disc or ligamentous structures in cases of significant neurologic injury.

Neurologic Classification

The basis of the SLIC neurologic status focuses on the AIS, as shown in Figure 128-1 . This classification system is currently the most widely used method to describe SCI. A complete grade A SCI is defined as no sensory or motor function is preserved in sacral segments S4-5. The AIS grading system does not take into account other neurologic findings present in SCI such as spasticity, pain, or dysesthesias all of which contribute to functional recovery and quality of life.

Although widely used and highly reproducible, the AIS interpretation of neurologic status often oversimplifies neurologic symptoms. For example, classification of unilateral spinal cord injury or cauda equina remains difficult and often under represents the true severity of injury. To ameliorate these flaws, other scoring systems have been proposed in an attempt to improve neurologic classification and surgical decision making. Tsou and coworkers in 2012 incorporated neural impairment (scoring range from 2 to 10), pathomorphology (scoring range of 2 to 15), and canal sagittal diameter (millimeters) at the narrowest point of injury as a more detailed form of analysis. Although Tsou and coworkers overcame some surgical management flaws of the SLIC system with more stringent parameters, the large range of scoring and its complexity has limited its widespread use.

Management

Injury Types

Simple Compression Fractures

A compression fracture is the collapse of a vertebra as a result of axial loading forces upon a flexed spine ( Fig. 128-3 ). Compression fractures appear as wedge deformities of the vertebral body. These injuries occur in the setting of trauma but are more common in patients with osteoporosis, lytic lesions, or congenital bone disorders such as osteogenesis imperfecta.

A, Midsagittal MRI of a patient with subtle compression fractures at C6 and C7, showing edema in the vertebral bodies. No ligamentous injuries are evident. B, Midsagittal CT reconstruction showing a compression fracture of C7. Note that the dorsal elements show no evidence of diastasis.

Simple compression fractures involve the anterior superior or inferior end plates and presents with greater vertebral body height loss anteriorly than posteriorly as the anterior column fails in compression. The middle column is uninvolved and the fracture does not affect the posterior vertebral body wall. The posterior column also remains intact and the posterior ligamentous structures retain their integrity. There is no subluxation or significant ligamentous disruption.

Simple compression fractures manifest with neck pain but rarely present with neurologic deficits. Simple compression fractures are stable without significant vertebral body height loss, subluxation, or focal kyphosis. Patients are generally treated conservatively with external immobilization in a cervical orthosis. Upright radiographs are obtained in the cervical orthosis to establish a baseline and to assess for instability prior to discharge. These patients typically heal after 6 to 12 weeks of external immobilization, at which point they are reassessed with flexion-extension radiographs for glacial instability. Patients without evidence of motion or instability on flexion-extension radiographs are gradually weaned from external immobilization.

Burst Compression Fractures

With burst compression fractures, axial loading forces overcome the middle column disrupting the discoligamentous complex resulting in deformity and instability of the cervical spine. Burst fractures are high-energy compression fractures that involve the middle column and disrupt the posterior vertebral body wall ( Fig. 128-4 ). Injury to the posterior cortex seen in burst fractures can result in retropulsion of bone into the spinal canal. Widening between the pedicles is also frequently observed. In these cases, the posterior ligamentous complex is often intact, but instability may ensue from significant kyphosis, vertebral body height loss, and spinal canal compromise. There is no widening of the space between the facet joints or the spinous processes to suggest posterior ligamentous complex injury as is seen in a teardrop fracture, which will be discussed later.

Plain radiograph ( A ), sagittal MRI ( B ), and CT scan ( C ) of a burst/axial compression injury at C3. Note retropulsion of the vertebral body on the axial CT ( C ). Although a laminar fracture is present, there is no evidence of widening of the dorsal elements on the plain radiograph or MRI. The injury was treated with a corpectomy of C3 followed by strut grafting and ventral cervical plating ( D and E ).

Burst compression fractures may present with neck pain, radiculopathy, or spinal cord injury. Treatment of burst fractures is based on neurologic as well as spinal stability. In neurologically intact patients without significant vertebral body height loss (< 40%) or kyphosis (< 20 degrees), the injury may be amenable to treatment with external immobilization in a semirigid or rigid (Halo or Minerva) cervical orthosis. Baseline upright radiographs are obtained to assess for stability and used for close follow up typically at 4 to 6 week intervals. Severe compression fractures may develop progressive kyphosis and vertebral body collapse, therefore early and close interval follow-up is indicated.

Burst fractures resulting in incomplete spinal cord injury necessitate early closed and open reduction and decompression. Ligamentotaxis from traction can partially reduce retro-pulsed bone fragments present in the spinal canal but rely on the competency of the posterior longitudinal ligament. Certain cases of traumatic kyphosis can also be improved with the application of traction.

Data suggest that early decompression in incomplete spinal cord injury facilitates neurologic improvement. The most common surgical technique to decompress the spinal canal is through an anterior approach in order to directly access and remove the intruding fragments. The goal is to decompress the spinal canal by removing the retropulsed bone fragments and to reconstruct the spinal column to provide stability. This is achieved with a corpectomy and subsequent reconstruction and stabilization using ventral instrumentation.

The authors recommend surgical intervention in patients presenting with complete spinal cord injury. Early decompression for complete spinal cord injury does not pertain to improved neurologic outcomes in comparison to delayed decompression, but surgical intervention may result in improvement of one to two root levels below the level of injury compared to conservative management. Additionally, surgical decompression and stabilization can prevent delayed neurologic decline from spinal instability in complete spinal cord injury patients such as development or extension of a posttraumatic syrinx. For the aforementioned reason, the authors also recommend surgical stabilization in patients with significant vertebral body height loss (> 40%) or kyphosis (> 20 degrees) as this may result in chronic neck pain or delayed neurologic deficits in initially neurologically intact patients.

Teardrop Fractures

A flexion teardrop fracture is a severe form of compression fracture resulting from a high-energy flexion and axial loading injury to the cervical spine such as in a motor vehicle accident or diving headfirst. Flexion teardrop fractures are most commonly seen at the C5-6 level. In flexion teardrop fractures the anterior, middle, and posterior columns are frequently involved with concomitant disruption of the posterior ligamentous complex ( Fig. 128-5 ). This injury pattern has a high rate of neurologic compromise, spinal deformity, and anatomic instability. Unique radiographic findings of a teardrop fracture include injury to the anterior inferior edge of the vertebral body, associated subluxation and kyphosis, and widening of the facet joints or the spinous processes.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

Anatomy of Nerve Root Compression, Nerve Root Tethering, and Spinal Instability Ventral and Ventrolateral Subaxial Decompression Diffuse Idiopathic Skeletal Hyperostosis Spinal Dural and Extradural Vascular Malformations Spinal Wound Closure Explant Analysis of Wear, Degradation, and Fatigue in Motion Preserving Spinal Implants

Stay updated, free articles. Join our Telegram channel

Join