MRI is highly sensitive to soft tissues, especially for edema.⁸^–¹⁰ MRI is the best method for visualizing the spinal cord. Compression or deformity of the spinal cord, edema, and hemorrhage are visualized well with MRI. It is also excellent for evaluating the intervertebral discs (Fig. 171-1). For example, detection of an acute disc disruption may alter plans for the surgical approach.¹¹ Cases have been reported in which the reduction of a dislocation worsened symptoms because of further herniation or displacement of disc material. MRI permits detection of such herniation before surgery. Ligament disruption can occasionally be directly visualized with MRI, especially the anterior and posterior longitudinal ligaments. Some evidence suggests that the extent of ligament disruption may correlate with the risk of instability in cervical spine dorsal element fractures.

FIGURE 171-1 Traumatic disc and ligament disruption. Sagittal fast inversion-recovery MRI shows disruption of both anterior and posterior longitudinal ligaments at C5-6 and disc disruption with traumatic disc herniation and ventral and dorsal soft tissue edema. The findings were confirmed at surgery.

The soft tissues around the vertebra are also visualized with MRI. Extensive edema can serve as a marker for acute injury and the need for further evaluation. Deep, interspinous edema in the setting of acute trauma may be an indication of high risk of instability due to flexion injury. Tears or stretching of the anterior and posterior longitudinal ligaments are especially concerning for instability. MRI can be helpful in a variety of clinical situations in which the combination of clinical and initial imaging findings is ambiguous or nondefinitive. For example, degenerative changes are very common in the cervical spine and can make detection of acute fractures difficult. Although CT can help to identify fractures, subluxation or chronic deformity can still be a challenge. A negative MRI in such situations, showing no evidence of any significant nearby soft tissue edema, makes acute injury unlikely as a cause of subluxation. MRI can be especially helpful when clinical assessment is limited, such as in the obtunded or intubated patient.¹²

Unexpected worsening of neurologic status after spine trauma can be due to a variety of factors. MRI may reveal such causes as epidural hematoma, disc herniation, or spinal cord edema from infarction.

The limitations of MRI mentioned earlier can be overcome in most cases. Monitoring is essential in the acutely injured patient. MRI-compatible monitoring equipment is available. The patient must be screened for the presence of metallic devices or metal within the body that would preclude MRI. Although standard spine coils may not be usable with a cervical collar, other coils can still permit diagnostic images. Faster imaging techniques continue to be developed for MRI, and it is often not necessary or appropriate to use the same sequences for acute trauma patients that would be used for evaluation of degenerative disc disease, for example. The specific sequences to be used can be tailored to the clinical situation.

Although it is impossible to specify MRI parameters that should be used because of the great variety of manufacturers, machines, and software available, some broad principles apply. A T2-weighted sequence is important for detecting edema. Fast-spin echo imaging, in which multiple echoes are acquired during each pulse sequence, is nearly always used in standard spine imaging. Such sequences are much faster than spin echo sequences and produce excellent signal-to-noise and high-quality images. Fast-spin echo sequences can be excellent for visualizing the spinal cord, for example. However, it is important to note that fat remains very bright on such sequences, even with T2-weighting. Therefore, if adjacent soft tissue edema is to be demonstrated, different sequences must be used that suppress the signal from fat (Fig. 171-2). A fat saturation pulse can be added to fast-spin echo imaging sequences. Alternatively, inversion recovery sequences (short-tau inversion recovery [STIR]) accomplish the same effect of heavy T2 weighting and fat suppression.

FIGURE 171-2 Fat suppression MRI for soft tissue evaluation. MRI was performed on a young man with myelopathic symptoms after a motor vehicle accident. A, Sagittal fast-spin echo T2-weighted image shows slight subluxation at C6-7, but edema from soft tissue injury is difficult to identify because fat also remains bright. B, On a sagittal fast-spin echo inversion-recovery image the fat is now dark, but edema in the dorsal soft tissues, the marrow space of upper thoracic vertebral bodies, and prevertebral space is very conspicuous. Anterior and posterior longitudinal ligaments at C6-7 are stretched (arrows).

Edema within the bone marrow is also well demonstrated with MRI. This appears as low signal (dark) on T1-weighted images, replacing the normally bright signal from fat in the marrow and high signal on fat-suppressed T2-weighted images. Acute fractures, especially those that involve the vertebral body, cause marrow changes, but bone contusions that do not result in cortical bone disruption can also result in marrow edema. Over time, marrow signal intensity usually returns to an appearance close to that of normal vertebral body marrow. Thus, signal intensity in marrow of a compressed vertebral body that matches that of adjacent, normal vertebrae provides evidence for a chronic rather than an acute injury.

The sensitivity of MRI for acute soft tissue injury depends on several factors. Edema resolves over several days; the precise time course has not been defined but clearly depends on the severity of the original injury. In our experience, soft tissue edema associated with an acute cervical spine injury is likely to be less extensive on MRI in the setting of axial load injuries. Presumably, this is due to less stretching and tearing of the soft tissues. For example, a minimally displaced Jefferson burst fracture may result in very little soft tissue edema. When these limitations are understood, however, MRI can play a very useful adjunct role in assessing major acute cervical spine trauma.

Motion Radiography Studies

Radiographs of the spine in different positions (i.e., flexion and extension views in a lateral position) are excellent for evaluating the stability of the spine in a delayed or chronic setting (Fig. 171-3). Such studies have significant limitations in the acute setting, however. Most importantly, they pose major risks if the spine is in fact unstable. Complications of flexion-extension radiographs are rare but well known. If motion studies are to be undertaken, it is highly desirable that the patient be fully alert, cooperative, and capable of controlling or stopping the motion. If flexion and extension are performed on an obtunded or comatose patient, performing the study under fluoroscopy should improve the safety. The motion can be immediately stopped as soon as subluxation or abnormal movement is visualized. However, data on the safety and accuracy of performing motion radiography on an obtunded patient in the setting of acute injury are very limited. Such studies are often time-consuming, and visualization of the cervicothoracic junction is frequently difficult.

FIGURE 171-3 Instability on flexion film. Flexion lateral radiograph obtained on a delayed basis after cervical spine trauma shows focal kyphosis and dorsal widening. Alignment in neutral position was normal.

A second limitation in the acute setting is a high incidence of muscle spasm or guarding. From one quarter to one third of patients with acute cervical spine injury may have nondiagnostic results because there is inadequate movement of the neck to assess stability.¹³ Delayed studies, several weeks after trauma and after muscle spasm has subsided, with the patient cooperative and in control of neck motion, remain the gold standard for evaluating the stability of the cervical spine.

Myelography

Because of the availability of MRI, myelography has a very limited role in the evaluation of spine trauma. There are occasional situations in which patency of the spinal canal must be assessed and MRI is not possible.

Imaging Findings

Cervicocranial Junction and Upper Cervical Spine

Upper cervical spine injuries can be multiple, complex, and difficult to identify on imaging.

C1 Fractures

The Jefferson burst fracture of C1 is a relatively common injury. CT can demonstrate the multiple fractures of the ring of C1 and the extent of displacement (Fig. 171-4). Plain films usually show prevertebral soft tissue swelling. Some components of the fractures can be visible on plain radiographs, more so if the fractures are displaced. The lateral masses of C1 are likely to be displaced laterally if the transverse ligament is disrupted. Total displacement of greater than 7 mm as seen on an odontoid view has been suggested as a guideline to the presence of transverse ligament rupture.¹⁴ The transverse ligament can be visualized directly on MRI, and fluid signal in place of the expected low signal intensity of the ligament is evidence of rupture.¹⁵

FIGURE 171-4 Jefferson fracture. Patient fell from a ladder onto the head. CT shows multiple fractures of the ring of C1.

The imaging findings just described apply to adults. In at least the first 4 years of life, the lateral masses of C1 often project lateral to the lateral margins of C2 on an AP view.¹⁶ Because Jefferson fractures are uncommon in children, CT may be necessary to demonstrate such fractures in children.

Isolated fractures of the dorsal arch of C1 can occur with hyperextension injuries (Fig. 171-5). In such cases, prevertebral soft tissue swelling would likely be absent, and the dorsal arch fracture can be seen on a lateral radiograph. Another type of hyperextension injury at C1 is an avulsion at the ventral caudal portion of the ventral arch, at the attachment of the atlantoaxial ligament. In this case, the fracture is visible on the lateral view, and focal prevertebral soft tissue swelling is usually present.

FIGURE 171-5 Dorsal arch C1 fracture. Extension mechanism: CT shows bilateral fractures through the dorsal arch of C1; the ventral arch was intact.

Transverse Ligament Injury

Transverse ligament rupture can be seen in association with a variety of upper cervical spine fractures, and this possibility should be considered in any such injury. In addition, transverse ligament injury uncommonly may occur without other fractures. Loss of integrity of the transverse ligament can result either from rupture in the midportion of the ligament or from avulsion of the ligament at one of the attachments to the lateral mass of C1. In the latter case, a small fracture is often visible at the tubercle where the ligament attaches (see Fig. 171-26). If the ventral atlantodental space is widened, transverse ligament rupture should be suspected. The ligament itself can be seen directly using MRI. In the case of rupture, fluid signal intensity (bright on T2-weighted images) can be seen in the expected location of the ligament, and fluid is also likely to be present between the dens and ventral arch of C1.

FIGURE 171-26 Transverse ligament avulsion. A, CT shows an avulsion fracture at the site of insertion of the transverse ligament on the left side (arrow). B, Coronal CT reconstruction demonstrates the displaced bone fragment (arrow).

C2 Fractures

Odontoid fractures can occur from a variety of mechanisms. Anderson and D’Alonzo ¹⁷ described three types of odontoid fractures: type I, an oblique fracture near the apex of the dens; type II, a transverse fracture through the lower third of the dens but above the body of C2 (Fig. 171-6); and type III, which is a fracture below the base of the dens and through the body of C2 (Fig. 171-7). As with transversely oriented fractures elsewhere, odontoid fractures can be difficult to identify by CT. Axial images may show only a region of lucency or subtle gaps in the cortical margin. Reconstructed images from thin-slice axial images, especially from rapid spiral acquisitions, can be very helpful for identifying odontoid fractures on CT. Plain radiographs should be carefully inspected for signs of odontoid fractures, including prevertebral soft tissue swelling, abnormal angulation of the odontoid process, offset of the dens with respect to the body of C2, and disruption of the cortical margin. The type III fracture (or type 3 C2 body fracture) is a horizontally oriented, rostral fracture at the base of the dens. In such fractures, the lateral radiograph shows a break in the apparent ring that results from the superimposition of densities from the junction of the pedicle and body, dens and body, and dorsal cortex of the C2 body.¹⁸ The AP or odontoid view usually shows a fracture with inferior convexity.

FIGURE 171-6 Type II dens fracture. Motor vehicle accident victim with neck pain: A, Anteroposterior radiograph shows fracture across the base of the dens. B, Lateral radiograph shows marked prevertebral swelling, fracture, and dorsal displacement of the dens relative to the body of C2. C, Axial CT discloses a fracture line through the dens. D, Sagittal CT reconstruction view shows the fracture and displacement. E, Sagittal short-tau inversion-recovery MRI shows the fracture, extensive prevertebral and lesser amount of dorsal edema, and relationship of the dens to the spinal cord.

FIGURE 171-7 Low dens (type III) fracture. Motor vehicle accident patient: A, Lateral radiograph shows lucency that disrupts the ring appearance (arrow), unlike the type II fracture in Figure 171-6. B, The low fracture, actually a fracture through the rostral portion of the body of C2, is easily seen in the anteroposterior view (arrows).

Fractures of the body of C2, which have received relatively little attention, include coronally oriented dorsal fractures (type 1), which are similar in some respects to the hangman’s fracture through the pars interarticularis of C2 (Fig. 171-8); oblique, sagittally oriented fractures (type 2), which result from axial loading (Fig. 171-9)¹⁹; and the horizontally oriented type 3 fracture described earlier (see Fig. 171-7). CT is particularly helpful in defining the location and extent of fractures in C2 body fractures.

FIGURE 171-8 C2 body fracture, type I. A, Lateral radiograph shows lucency in the dorsal body of C2, with prevertebral soft tissue swelling. B, CT shows fractures through the dorsal portion of the C2 body.

FIGURE 171-9 C2 body fracture, type 2. Axial CT of a patient who fell from a ladder onto his head shows an oblique fracture through the C2 body, with an additional fracture through the left lamina.

The hangman’s fracture, or traumatic spondylolisthesis, consists of bilateral fractures through the pars interarticularis (Fig. 171-10).^20,²¹ It is usually visible on lateral radiographs as a lucency, with prevertebral soft tissue swelling. The Effendi classification of these fractures is based on the extent of displacement: type I consists of minimal displacement; type II shows ventral displacement and an abnormal C2-3 disc; and type III is ventral displacement of the body of C2 in flexion, with bilateral facet dislocation of C2-3.²²

FIGURE 171-10 Traumatic spondylolisthesis (hangman’s fracture). A, Lateral radiograph shows fractures through the pars interarticularis, with ventral displacement of the body of C2 relative to C3 in this case. B, Axial CT in this case shows bilateral fractures through the pars interarticularis.

The extension teardrop fracture of C2 consists of an avulsion of the ventral caudal corner of the C2 body at the attachment of the atlantoaxial ligament. A characteristic triangular shape is evident on lateral radiographs, usually with accompanying prevertebral soft tissue swelling.

Children can suffer a unique injury of C2, fracture through the subdental synchondrosis. The dens is separated in a sharp, geometric margin from the centrum of C2 below (Fig. 171-11).

FIGURE 171-11 C2 synchondrosis fracture in an infant. An unrestrained infant in a motor vehicle crash had abnormalities at the C2 level on plain film. A, Axial CT shows fractures that mostly involve the neurocentral synchondrosis, separating the body and odontoid from the neural arch. B, 3D reconstruction from below shows the separation through the synchondrosis. The ventral aspect of the spine, including the ventral arch of C1, has been excluded to allow visualization of C2.

Craniocervical Junction

Occipital condyle fractures are especially difficult to identify on plain radiographs. CT with thin-slice thickness and reconstruction images is the best imaging tool (Fig. 171-12). Occipital condyle fractures have also been classified in three groups. Type I fractures are compression fractures from axial loading. Type II fractures are basilar occiput fractures that extend into the occipital condyle. Type III fractures result from avulsion, a result of lateral bending and forced rotation. Because of ligamentous injury, type III are the condyle fractures most likely to be unstable.^23,²⁴

FIGURE 171-12 Occipital condyle fracture. A, Axial CT shows lucency in the right occipital condyle. B, Coronal reconstruction demonstrates more clearly the oblique right occipital condyle fracture.

Atlanto-occipital dislocation is often a fatal injury, although less severe forms are increasingly being recognized. Prominent upper cervical prevertebral soft tissue hematoma is nearly always present (Fig. 171-13). Several methods of measuring atlanto-occipital dislocation have been proposed. The Powers ratio is the relationship of the distance from basion (B) to the dorsal arch of the atlas (C), compared with the distance from opisthion (O) to the midpoint of the dorsal surface of the ventral arch (A).²⁵ The ratio BC/OA, which is normally less than 1, increases with ventral dislocation. The bony landmarks to determine the Powers ratio can be difficult to identify, and Harris and colleagues have described two measurements that are easier to perform and less sensitive to the direction of dislocation.^26,²⁷ Both measurements are performed on a lateral radiograph (Fig. 171-14). The first is between a dorsal axial line upward from the dorsal vertebral body of C2 and the basion. The basion-axial interval should be no less than 6 mm or more than 12 mm, in both adults and children. The second measurement is between the basion and the tip of the dens, the basion-dens interval. This distance should not be more than 12 mm. This basion-dens interval depends on complete ossification of the dens and therefore may not be obtainable in children younger than 13 years. Evaluation with multidetector CT is somewhat different.²⁸ The normal basion-dens interval is less than 8.5 mm in 95% of the normal adult population. The basion-axial interval is less reliable and useful on CT. The atlanto-occipital interval, or distance between the occipital condyle and C1 lateral mass at the midpoint of the joint, should be less than 1.5 mm. The relationship between the condyle and C1 lateral mass is readily assessed on parasagittal CT reconstructions and should be evaluated routinely (see Fig. 171-13C).

FIGURE 171-13 Atlanto-occipital dissociation. A, Axial CT through the cervicocranial junction is most remarkable for what is not present—little bone is visible at what should be the atlanto-occipital joint. B, Sagittal CT reconstruction demonstrates distraction between the tip of the clivus and the tip of the dens. C, Subluxation of the atlanto-occipital joint is demonstrated on a parasagittal view. D, Sagittal inversion-recovery MRI shows extensive ventral and dorsal soft tissue edema, disruption of the tectorial membrane, and the effect of the dissociation on the spinal cord. E, A parasagittal image from the same MRI sequence as part D demonstrates fluid in the disrupted joint space.

FIGURE 171-14 Craniocervical relationships and atlanto-occipital dissociation (AOD). Lateral radiograph of a patient who suffered AOD shows severe prevertebral soft tissue swelling and distraction of the cranium from the spine. Measurements described by Harris et al.^26,²⁷ are illustrated: A, Basion-axial interval, distance from basion to a line extended upward from the dorsal margin of the body of C2. B, Basion-dens interval, distance from basion to the tip of the dens.

Subaxial Cervical Spine Injuries

Axial loading injuries in the lower cervical spine result in burst fractures. The basic pattern of the burst fracture is similar throughout the thoracic and lumbar spine, as well. The degree of comminution is variable, but there is usually a prominent sagittal component. Dorsal element fractures are common and variable. CT is very helpful in determining the extent of fractures (Fig. 171-15). Involvement of multiple vertebrae can occur with more severe injuries. MRI can directly demonstrate the relationship of displaced bone to the spinal cord, spinal cord compression, and spinal cord edema and hematoma, as well as disc disruption.

FIGURE 171-15 Burst fractures. A, CT of a patient in a motor vehicle accident through the C4 level reveals minimally displaced fractures, including sagittal fracture through the body and fracture of the right lamina. B, Coronal reconstruction shows the sagittally oriented fracture. C, CT at the C5 level of a different patient, who fell from a considerable height, shows much more comminuted and displaced pattern. D, Sagittal reconstruction shows displacement of bone into the spinal canal in this case. E, Sagittal fast-spin echo T2-weighted MRI of the second patient additionally shows the edema and possible hemorrhage within the spinal cord.

A variety of flexion injuries can occur in the subaxial cervical spine. Many of these injuries result in a pattern of dorsal widening or fanning of the facets and spinous processes at the level of injury (Fig. 171-16). This pattern of flexion injury is an important finding on lateral radiographs. Dorsal ligament injury without fracture can result in instability from flexion sprain. A simple ventral compression fracture results in loss of ventral height of a vertebral body. Dorsal ligament injury may or may not accompany a compression fracture. Focal kyphosis is often observed at the level of compression.²⁹^–³¹A fairly common pattern of flexion injury in the lower cervical spine is an avulsion fracture of the spinous process, or “clay-shoveler’s fracture.”

FIGURE 171-16 Flexion sprain. Lateral cervical spine radiograph demonstrates kyphosis and dorsal widening at C5-6, and to a lesser extent at C6-7.

More serious flexion injuries can cause actual disruption of the facet joints and bilateral facet dislocation (Fig. 171-17). The vertebra above the level of dislocation is ventrally displaced relative to the vertebra below the level of dislocation. Dorsal widening and focal kyphosis are observed. CT often reveals small fractures of the articular processes at the level of dislocation. MRI shows a typical pattern of extensive dorsal soft tissue edema from the level of dislocation and above; and the relationship of the spinal cord to the narrowed spinal canal can be seen on MRI.

FIGURE 171-17 Bilateral facet dislocation. Patient was quadriplegic after motor vehicle accident. A, Axial CT shows reversal of the normal relationship of the facets bilaterally. B–D, Sagittal CT reconstruction views, (left, midline, and right, respectively) show greater than 50% subluxation of C4 on C5, bilateral facet dislocation, and fracture of the left C5 lateral mass. E, Sagittal inversion-recovery MRI shows spinal cord compression and edema and extensive soft tissue edema in addition to the subluxation and stretching of anterior and posterior longitudinal ligaments. F, Axial source image from magnetic resonance angiography of the same patient demonstrates no flow in the right vertebral artery, with intact flow in the left vertebral and bilateral carotid arteries.

A flexion teardrop fracture is one of the most severe flexion injuries of the cervical spine. Lateral radiographs show a large triangular fragment of bone from the ventral caudal corner of the fractured vertebra. Unlike the extension teardrop fracture, there is pronounced flexion of the spine at the level of injury. The typical clinical picture of anterior cord syndrome also distinguishes the flexion teardrop fracture.³²

Extension mechanisms can cause a variety of cervical spine injuries. Compression of the lamina can cause laminar fractures, visible on lateral or oblique radiographs, and especially CT.

Hyperextension dislocation causes transient dislocation through a disc level and compression of the spinal cord. The usual clinical picture is a central cord syndrome. Radiographic signs are straightening of the cervical spine, diffuse prevertebral swelling, and often an avulsion fracture of the inferior end plate above the level of dislocation (Fig. 171-18). Such a fracture is horizontally oriented and is wider than it is tall. Disc space widening or gas within the disc space is less commonly seen.^33,³⁴ MRI shows the prevertebral edema, abnormal signal in the affected disc space, and edema within the spinal cord. In the author’s experience, MRI also often shows dorsal soft tissue edema. Another cause of central cord syndrome resulting from hyperextension was described by Taylor et al.^35,³⁶ In such cases, preexisting osteophytes narrow the spinal canal and cause transient spinal cord compression. Diffuse prevertebral soft tissue swelling is lacking in such cases, but MRI shows edema within the spinal cord and the extent of spondylosis (Fig. 171-19).

FIGURE 171-18 Hyperextension dislocation (hyperextension sprain). Lateral (A) and swimmer’s (B) views of this patient who had a central cord syndrome after a motor vehicle accident show straightening of the cervical spine and diffuse prevertebral swelling. C, Sagittal inversion-recovery MRI of a different patient with hyperextension injury but no spinal cord injury shows disruption of the C6-7 disc space and anterior longitudinal ligament, with both prevertebral and dorsal edema.

FIGURE 171-19 Central cord injury from Taylor mechanism. A man who fell and suffered a hyperextension injury with a central cord syndrome. Sagittal T2-weighted MRI shows spondylosis and spinal stenosis in the lower cervical spine and edema in the spinal cord.

Unilateral facet dislocation results from combined flexion and rotation. Such cases have a typical constellation of imaging findings (Fig. 171-20).^37,³⁸ Lateral radiographs show an abrupt change from a typical lateral appearance below the dislocation to an appearance above that level of an oblique projection. The visualization of both facets on the lateral view just above the dislocation gives a “bow-tie” appearance. On the AP view, there is an abrupt change in the line along the spinous processes. CT shows a reversal of the usual “clamshell” appearance of the facets where they are dislocated. In less severe cases, the facets may appear “perched” without frank dislocation, but this finding still implies major ligament and joint disruption.

FIGURE 171-20 Unilateral facet dislocation. A, CT through the C6-7 level of a young man after a motor vehicle accident shows dislocation of the right facet joint, with reversal of the normal relationship of the facets. B–D, Sagittal CT reconstructions from left to right show mild subluxation on the left side (B), mild anterolisthesis in the midline with dorsal splaying (C), and facet dislocation on the right (D), with a small bone fragment dorsal to the dislocation. E, On sagittal inversion-recovery MRI the extent of ligamentous injury and edema is easily seen, with no evidence of spinal cord edema or compression. F, Anteroposterior radiograph shows a characteristic abrupt change in alignment of the spinous processes. The initial lateral radiograph (not shown) was obscured by the shoulders, but typical findings of unilateral facet dislocation are demonstrated on a different patient (G) who had dislocation at C5-6. There is an oblique orientation of the spine above this level and a straight lateral configuration below this level. Note the “bow-tie” shape of the articular processes above the level of dislocation.

Fractures involving the lateral masses, pedicles, and laminae can be very difficult to visualize on plain films. Close inspection of the lateral bony margins seen on AP views can show irregularity or overlap in some cases. If there is more extensive ligament injury and displacement, there may be rotational displacement that can simulate a unilateral facet dislocation on plain films. However, CT clearly demonstrates the location of fractures (Fig. 171-21). Fractures of both pedicle and lamina result in separation of the articular mass from the vertebral body and potential instability. MRI can be helpful in determining the extent of ligamentous injury, which may help predict the risk of instability.³⁹

FIGURE 171-21 Pedicolaminar fractures. A, Axial CT of a motor vehicle accident patient shows fractures involving the pedicle and lamina on the patient’s left side. There was spinal cord injury and rotational instability. B, Ligamentous injury and spinal cord edema are visible on sagittal inversion-recovery MRI.

The injuries just described are those seen in some of the more common patterns of cervical spine injury. It is important to remember that fractures commonly occur at more than one level.

Identification of a fracture should not terminate the evaluation of the entire cervical spine.

Thoracic and Lumbar Spine

Indications for screening of the thoracic and lumbar spine in the setting of blunt trauma are not as clear-cut as in the cervical spine.^40,⁴¹ In the trauma patient with back pain, a good starting point for evaluation of thoracolumbar trauma is high-quality AP and lateral radiographs. However, if the patient is already getting chest/abdominal CT imaging, reconstructed axial bone windows with high-quality sagittal and coronal reformats are superior to plain radiography for the exclusion of trauma. In most cases, it suffices to obtain plain radiographs to screen the thoracolumbar spine in the obtunded or intoxicated patient and in the patient with unreliable clinical examinations.⁴⁰ Dedicated CT imaging of the thoracolumbar spine is usually reserved for patients with significant plain radiographic abnormalities, usually as a part of presurgical planning. In the setting of neurologic deficits, MRI is often indicated to exclude entities such as direct spinal cord injury, traumatic disc herniation, or epidural hematoma. In contrast to the cervical spine, MRI is not usually needed to exclude ligamentous injury if there is no associated fracture of the spine.

Along with more restricted movement in the thoracic and lumbar spine than in the cervical region, there exist fewer patterns of fracture. Compression fractures and burst fractures have features similar to those described for the cervical spine. Prevertebral soft tissue swelling is not a very useful plain film finding below the cervical spine, but paraspinal soft tissue hematoma can be visible on AP views, especially in the thoracic spine. With compression fractures, ventral loss of height and buckling of the superior end plate and ventral cortical margin occur (Fig. 171-22). In more severe cases, some dorsal buckling of the vertebral body is observed. There is usually focal kyphotic angulation. Mild compression fractures are often more obvious on lateral radiographs than on CT. CT may show only subtle lucency along the ventral, superior margin of the vertebral body in mild fractures. MRI or bone scan can be helpful in resolving any uncertainty about whether a fracture is acute or chronic. Edema will be seen in the marrow space on MRI in acute fractures; after a period of weeks to months, the marrow signal intensity returns to that similar to adjacent, normal marrow.

FIGURE 171-22 Thoracic compression fracture. A, Lateral radiograph of the lower thoracic spine shows mild ventral loss of height of T11 and buckling of the ventral cortical margin. B, Chest radiograph shows subtle paraspinous widening at T11 (arrows). C, Axial CT of T11 shows fractures only in the ventral body. D, Sagittal CT reconstruction shows mild ventral loss of height and superior end-plate and ventral rostral cortical disruption.

Burst fractures are usually visible on plain films, but CT can much more fully characterize the vertebral body fractures, degree of comminution and displacement, and dorsal element fractures (Fig. 171-23). Fractures of adjacent vertebrae are common, so CT should include enough of the nearby spine to ensure that all fractures near the obvious injury have been detected. This is of obvious value in planning instrumentation. MRI yields additional information about the integrity (or loss thereof) of discs and major ligaments as well as spinal cord damage.

FIGURE 171-23 T10 burst fracture. A, CT of a paraplegic after motor vehicle accident shows burst fracture of T10, with severe narrowing of the spinal canal from a large bone fragment. B, Subsequent sagittal inversion-recovery MRI shows severe spinal cord compression and edema, with relatively little dorsal soft tissue edema. Note the alignment, without the kyphosis often accompanying compression fractures.

Chance-type injuries are characterized by dorsal distraction in combination with flexion. The most common locations are around the thoracolumbar junction. The classic fracture described by Chance extends in a horizontal plane through a vertebral body into the pedicles (Fig. 171-24).⁴² These fractures are often more easily appreciated on lateral radiographs than on the axial CT images. Since the fractures lie in the plane of imaging, axial images may be notable only for an absence of bone rather than distinct fracture lines. Sagittal and coronal reconstruction images show the fractures on CT more clearly than the axial images. However, the category of Chance-type injuries has been broadened to include other injuries that result from a similar mechanism.^43,⁴⁴ Thus, the horizontally oriented disruption can also occur through an intervertebral disc, and the plane of dorsal distraction then typically extends through the facet joints. In any of these patterns, MRI demonstrates localized injury through the dorsal elements and soft tissues. In addition, a Chance injury should always suggest the possibility of associated abdominal injuries. Solid organ lacerations and perforations are present in up to half of patients with Chance-type injuries.