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Chapter 19Spinal Trauma and Spinal Cord Injury (SCI)
Luc van Den Hauwe, Pia C. Sundgren, and Adam E. Flanders.Author Information
AuthorsLuc van Den Hauwe,1 Pia C. Sundgren,2 and Adam E. Flanders3.Affiliations
The majority of the spinal injuries (60%) affect young healthy males between 15 and 35 years of age with cervical spine injuries to be most common. The main cause for spinal injuries is blunt trauma most commonly due to motor vehicle accidents (48%) followed by falls (21%), and sport injuries (14.6%). Assault and penetrating trauma account for approximately 10–20% of the cases. Injuries to the spinal column and the spinal cord are a major cause of disability, affecting predominately young healthy individuals with important socioeconomic consequences and the costs of lifetime care and rehabilitation exceed one million US dollars per patient excluding financial losses related to wages and productivity. Over the past several decades, the mean age of the spinal cord injured patient has increased which is attributed to a substantially greater proportion of injuries related to falls in the elderly. Cervical spine injuries, of which approximately one-third occur in the craniocervical junction (CCJ) (Riascos et al., Radiographics 35:2121–2134, 2015), account for the majority of the spinal injuries followed by thoracolumbar fractures. Almost half of the spinal injuries result in neurological deficits, often severe and sometimes fatal (Hill and Dean, J Trauma 34:549–554, 1993). Survival is inversely related to the patient’s age, and neurologic level of injury, with lower overall survival for high quadriplegic patients compared to paraplegic injuries. Mortality rate of spinal cord injury during the initial hospitalization is reported to be almost 10% (Pope and Tarlov, Disability in America: toward a national agenda for prevention, National Academy Press, Washington, 1991). Injury to the spinal cord occurs in 10–14% of spinal fractures and dislocations with injuries of the cervical spine being by far the most common cause of neurological deficits (40% of cervical injuries) (Riggins and Kraus, J Trauma 17:126–130, 1997; Castellano and Bocconi, Bull Hosp J Dis Orthop Inst 31:188–198, 1970). The majority of injuries to the spinal cord (85%) occur at the time of trauma, whereas in a minority of cases (5–10%) the spinal cord injury occurs in the immediate post-injury period (Rogers, J Bone Joint Surg 39:341–351, 1957). The imaging methods for evaluating patients with acute spinal trauma have dramatically changed in the last decade especially with the development of thin section multi-detector computed tomography (MDCT) and isotropic datasets that provide high-resolution sagittal and coronal reformats. MDCT allows for a comprehensive assessment of spinal column injury that has largely supplanted radiography except in the pediatric population. Magnetic resonance imaging (MRI) has become the procedure of choice for evaluation of the spinal cord and surrounding soft tissues when a reliable neurologic examination cannot be performed.
Keywords:Trauma, Spinal injury, Spinal cord injury, MRI, CT, Vertebral body fractures, Ligamentous injury, Traumatic disc herniation, SWICORA, Neurological deficits
To appreciate the utility of radiography, computed tomography, and magnetic resonance imaging in the evaluation of spinal trauma and spinal cord injury.
To appreciate the soft tissue components of spinal trauma and how they differ in the pediatric population.
19.1. Imaging Modalities for Spinal Trauma
In the emergency setting the appropriate selection of imaging for spinal trauma depends upon several factors such as, modality availability, the patient’s clinical and neurological status, type of trauma (blunt, single, or multi-trauma), and other associated co-morbidities. Clinical factors to consider also include the quality and severity of pain, limitations in motion, or the presence of permanent or transient neurological deficits. MRI is reserved for those patients with post-traumatic myelopathy (spinal cord dysfunction) or in the instance whereupon a patient’s symptoms that cannot be explained by findings on radiographs or CT, or when a reliable neurologic exam cannot be obtained.
19.1.1. Plain Film Radiography
In the rare circumstance where MDCT is not available, the initial imaging modality is radiography. A minimum of a lateral and anteroposterior view must be obtained for the spinal axis with the addition of an open-mouth odontoid view for the cervical spine. Often additional views such as oblique views and/or the swimmer’s view are performed in an attempt to clear the cervicothoracic junction. With the exception of pediatric trauma, in most settings, radiography has been supplanted by MDCT.
19.1.2. Computed Tomography (CT)
Thin section multi-detector computed tomography (MDCT) is the preferred method when evaluating the cervical spine for bony injury after blunt trauma. The entire spinal axis can be reliably and expeditiously evaluated with automatic reformatting of the axial dataset into multiple planes allows for better and more exact diagnosis of bone- and soft tissue abnormalities <7–13>. Moreover in the instance of polytrauma, spine images can be reconstructed directly from chest, abdomen, and pelvis datasets with sensitivity that is equivalent to a dedicated spine CT study. This has the added benefit of minimizing radiation dose.
With the introduction of these new MDCT imaging techniques most trauma centers have set up dedicated acute (multi-) trauma protocol(s) which include CT of the brain, cervical spine, thorax, abdomen, and pelvis, with subsequent reformatting of images of the thoracic and lumbar spine. This both expedites the data acquisition for medically unstable patients and serves to minimize radiation dose since the body imaging data can be reconstructed offline into targeted spine reconstructions. CT has a higher sensitivity to fractures (especially involving the posterior elements) than radiography. This rapid cross-sectional imaging assessment of the spinal axis has been shown to be more efficient and safer by virtually eliminating the need for repeat radiographs and unnecessary patient transfers in the setting of an unstable spine. Moreover, the diagnostic quality of radiography varies considerably, is more time-consuming to acquire, and may be difficult to perform in a medically unstable patient. While MDCT excels at delineating bony injury, it also can detect many soft tissue abnormalities such as disc herniation, paravertebral soft tissue- and epidural hematoma. A high-resolution CT imaging protocol begins with submillimeter overlapping partitions to create an isotropic dataset that yields identical spatial resolution in any reconstructed plane. Axial data can be reformatted into thicker sections for diagnostic display; with reformatted 1.25–2 mm thin slices in the C1–C2 region, 2–3 mm thin slices in the rest of the cervical spine, and 3–4 mm thin slices in the thoracic and lumbar spine are typically chosen for axial presentation. Reformatted sagittal and coronal images of the entire spine are produced from contiguous submillimeter (0.3–0.75 mm) axial images. Multiplanar reformatted (MPR) sagittal and coronal images of the entire spine are typically produced automatically from the scanning console or from a nearby workstation. Reconstructions are performed with both bone and soft tissue algorithms.
19.1.3. Magnetic Resonance Imaging (MRI)
The greatest impact that MRI has made in the evaluation of spinal trauma has been in assessment of the soft tissue component of injury. MRI is today considered the method of choice for assessing the spectrum of soft tissue injuries associated with spinal trauma. This includes damage to the intervertebral discs, ligaments, vascular structures, and spinal cord <14–16>. No other imaging modality has been able to faithfully reproduce the internal architecture of the spinal cord and it is this particular feature that is unique to MRI. Any patient who has a persistent neurologic deficit after spinal trauma should undergo an MRI in the acute period to exclude direct damage/compression to the spinal cord. MRI provides unequivocal evidence of not only spinal cord injury, but will also reliably demonstrate disc injuries/herniations, paraspinal soft tissue edema (ligament strain/failure), epidural hematomas, and vascular injury. In addition, MRI provides the most reliable assessment of chronic spinal cord injury and the imaging analogs of post-traumatic progressive myelopathy (PTPM) which is often manifested with imaging as syrinx formation, myelomalacia, and cord atrophy. The extent with which MRI is able to determine spinal instability is overstated as MRI is unable to provide a reliable assessment of ligamentous integrity in most cases. In fact, MRI falsely overestimates the soft tissue component of injury <17>.
An acute spinal trauma MR imaging protocol of the cervical spine shall include 3 mm thick sagittal T1 (T1-weighted) and T2-weighted (T2W) and short tau inversion recovery (STIR) sequences and 3 mm thick axial T2∗-weighted gradient echo (GRE) images without contrast. In the thoracic and lumbar spine, 4 mm thick sagittal T1-weighted, T2-weighted, and STIR sequences and axial 4 mm thick T1-weighted, T2-weighted, and T2∗GRE images without contrast is recommended. 3D volumetric axial GRE or T2-weighted partitions at 1–2 mm thickness are useful in the cervical region. Fat-saturated T2-weighted images are valuable to evaluate for ligamentous and soft tissue injuries, and T2∗ GRE to evaluate for small hemorrhage or blood products in the spinal cord.
Radiography has largely been supplanted by MDCT except in the pediatric population for evaluation of bony injury.
19.2. Different Grading Systems to Evaluate Spinal Injuries
There are different classic grading scales for determining spinal instability of thoracolumbar injuries based upon the McAfee (two-column) and Denis three column concept <18, 19>. The Magerl classification relies exclusively on CT findings <20>. In recent years a new grading scale that is based on CT and magnetic resonance (MR) imaging findings, like the thoracolumbar injury classification and severity score (TLICS) has been developed by the Spine Trauma Group <21> to overcome some of the perceived difficulties regarding the use of other thoracolumbar spinal fracture classification systems for determining treatment. Also for the grading of the cervical spine a new grading scale and score system—the cervical spine Subaxial Injury Classification and Scoring (SLIC) system <22>—has been developed and is gaining acceptance among spine surgeons. The AO Spine classification system provides a comprehensive classification schema for upper cervical, subaxial cervical, thoracolumbar, and sacral injuries <23>.
19.2.1. Injuries to the Vertebral Column
Classically, injuries to the spinal column are categorized by mechanism of injury and/or by instability. Instability is defined by White and Punjabi as abnormal translation between adjacent vertebral segments with normal physiologic motion. Unrecognized instability after trauma is a potential cause of delayed spinal cord injury. This is why early stabilization of the initial injury is an imperative to appropriate clinical management. The simplest method to test for instability in a controlled environment is by performing flexion and extension lateral radiography to produce a visible subluxation at a suspected level but this is rarely performed in practice.
From biomechanical point of view, the thoracolumbar spine can be divided into three osteo-ligamentous columns: anterior-, middle-, and posterior column <18>. The anterior column includes the anterior longitudinal ligament and anterior two-thirds of the vertebral body and disc including annulus fibrosus. The middle column is composed of the posterior third of the vertebral body and disc including annulus fibrosus, and posterior longitudinal ligament. Finally, the posterior column is composed of the pedicles, articular processes, facet capsules, laminae, ligamentum flavum, spinous processes, and the interspinous ligaments. The mechanism of injury will result in several different types of traumatic injuries to the cervical, thoracic, and lumbar vertebral column and spinal cord, which may result in stable or unstable spine injuries. Although this biomechanical model is often inferred for cervical injuries, there is no similar established model in the cervical spine.
Because of the distinct anatomic differences and the resultant injury patterns, injuries to the cervical spine are divided into subaxial injuries (cranial base to axis) and lower cervical injuries (C3–C7). The mechanism of injury to the cervical column can be divided into four major groups: hyperflexion, hyperextension, rotation, and vertical compression with frequent variations that include components of the major groups (e.g., flexion and rotation). Hyperflexion injuries include anterior subluxation, bilateral interfacetal dislocation, simple wedge fracture, fracture of the spinous process, teardrop fracture, and odontoid (dens) fracture. Of these the simple wedge fractures and isolated spinous process fractures are considered initially stable, while the other fractures are considered unstable such as the bilateral interfacetal dislocation and the teardrop fracture. The odontoid fracture can be considered stable or unstable depending on the type of fracture type. Hyperextension mechanism is less frequent than the hyperflexion and result in the following types of injuries: dislocation, avulsion fracture or fracture of the posterior arch of C1, teardrop fracture of C2, laminar fracture, and traumatic spondylolisthesis of C2 (Hangman’s fracture). Most of these injuries with the exception of Hangman’s fracture are defined as stable fractures; however, this does not imply that these injuries should go untreated. The hyperextension injuries are often associated with central cord syndrome especially in patients with pre-existing cervical spondylosis and usually produce diffuse pre-vertebral soft tissue swelling. Vertical compression results in the Jefferson fracture which involves atlas and is considered unstable or burst fractures. A common site for injuries is the craniocervical junction (CCJ) and the atlantoaxial joint, which is the most mobile portion of the spine as it predominantly relies on a complex ligamentous framework for stability. The imaging findings of important CCJ injuries, such as atlanto-occipital dissociation, occipital condyle fractures, atlas fractures with transverse ligament rupture, atlantoaxial distraction, and traumatic rotatory subluxation, are important to recognize in the acute setting as for the patient management.
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Fractures in the lower thoracic and lumbar spine differ from those in the cervical spine. The thoracic and lumbar fractures are often complex and due to a combination of mechanisms. The thoracic cage confers substantial biomechanical protection to the thoracic spine. Therefore, statistically, most injuries occur at the most mobile portion or the thoracolumbar junction where the thoracic cage ends. When injuries occur in the upper or middle thoracic spine it is usually a result of major trauma, e.g., high velocity trauma such as motor vehicular accidents. The most common fracture, at the thoracolumbar junction, is the simple compression- or wedge fracture (50% of all fractures) which is considered stable. The remaining types of fractures among those the so-called seat belt injury, which can be divided into three subtypes: type I (Chance fracture) involves the posterior bony elements, type II (Smith fracture) involves the posterior ligaments, and, in type III the annulus fibrosus is ruptured allowing for subluxation are considered unstable fractures <24>. With the advent of the three-point restraint system in motor vehicles, these severe hyperflexion-distraction injuries have become uncommon. The most common of all thoracolumbar fractures—the burst fractures account for 64–81% of all thoracolumbar fractures. The burst fracture, which can be divided into five subtypes, is associated with high incidence of injuries to the spinal cord, conus medullaris, cauda equina, and nerve roots <25>. It is important to remember that a burst fracture involving anterior and middle column can be misdiagnosed as mere compression fracture on plain films and, therefore may be misinterpreted as a simple compression or mild wedge fracture that involves only anterior column. CT has improved characterization of these injuries.