CT is significantly superior to radiography in terms of sensitivity, specificity, and diagnostic accuracy (Figs. 5.1 and 5.3). Axial, multiplanar 2D-, and 3D-reformatted CT images are the optimal tools to show the more complex anatomic regions of the spine, such as craniocervical (Fig. 5.6), cervicothoracic, and thoracolumbar junctions, as well as the classical anatomical model of the “three columns” of Denis [5] of the thoracic and lumbar spine (Fig. 5.7a), as well as the anatomic model of the “four columns” of the subaxial cervical spine (Fig. 5.7b) for the Cervical Spine Injury Severity Score [33]. CT may confirm the diagnosis of compression fracture at radiography or reclassify the lesion as a burst fracture (Fig. 5.1), with possible impact on the management plan. Similarly, only CT defines with certainty the fracture lines involving bone and joint components of the lateral arches (Figs. 5.3 and 5.4). Surely, CT is the best technique for the recognition of vertebral bony portions and fragments (Fig. 5.8), as well air or gas, which may not be recognized or wrongly interpreted as bone by MRI. Notably, also thanks to multislice technique and providing the most accurate assessment of the fine anatomy of the osseous spine, CT allows the identification of indirect signs of discoligamentous or capsular injury, sometimes hardly recognizable in lateral view radiographs, although CT analysis of the soft tissues is less accurate than that directly provided by MRI (Figs. 5.8, 5.9, 5.10, and 5.11) [9, 16, 20]. These reasons explain why CT is now considered the first-line procedure in polytrauma patients who however require CT of the head, chest, abdomen, and pelvis to rule out intracranial and visceral injuries.

Furthermore, thanks to technological progress and the availability of multislice CT scanners, a further advantage is the possibility of performing CT angiography (CTA) of cervicocranial arteries in patients with associated risk of blunt cerebrovascular injury [1, 3, 13, 36, 49]. An Italian study performed by a 16-slice CTA showed that blunt cerebrovascular injury occurred in more than 3% of 1153 patients admitted as multi-trauma, i.e., with two or more injuries (of which at least one life-threatening or Injury Severity Score ≥ 16) and/or high-speed trauma or fall from an height > 3 m [1]. Fractures, dislocations, and subluxation of the craniocervical junction and the cervical spine are among the conditions at risk (Figs. 5.10, 5.12, 5.13, and 5.14), including fractures of the transverse processes with involvement of the transverse foramen where the vertebral artery passes (Fig. 5.13). Other risk factors include injuries from high-energy trauma, such as LeFort fractures, fracture of the first rib and of the sternum, as well as associated signs of neck trauma suggesting hanging as the mechanism of injury. Catheter digital subtraction angiography is still considered the “gold standard” technique; however, it is relatively invasive, has a significant cost, requires specific resources, and is not always available. In the screening evaluation at the time of admission for trauma, it has to be replaced by modern-scanners multislice CTA [36]. CTA may be performed by a “whole body” or a sequential technique on the basis of institutional experience: always it has to include the aortic arch and cover the intracranial arterial vessels [1, 49].

Additionally, iodine contrast medium intrathecal injection, i.e., myelography completed by high-resolution CT myelography, may be still advocated for a more detailed evaluation of posttraumatic nerve root avulsions, especially in brachial plexus injuries, providing a support to somatosensory evoked potentials in prognosis and surgical exploration planning, especially when high-resolution MRI including MR myelography is contraindicated or provides uncertain findings [43, 60].

Finally, various potential pitfalls may mimic or mask spinal injuries at multislice CT [19], including anatomical and developmental variants resulting from failure of fusion or segmentation, vascular channels (Fig. 5.15), intervertebral discs, motion-related and beam-hardening artifacts, and non-traumatic or underlying conditions. The (neuro)radiologist has to be familial with such possibilities.

MRI is the only imaging procedure providing a direct study of the spinal cord and spinal root. Thus, it is indicated in patients with spinal cord symptoms and signs and in those with discrepancy between findings at radiography and/or CT and neurological clinical status [12, 15, 31, 39, 47].

High contrast resolution of MRI, especially in short tau inversion recovery (STIR) and fat-suppressed T2-weighted images, results in the further advantages of direct identification of posttraumatic bone edema, as well as intervertebral discs, ligaments, and joints lesions, even with normal findings at radiography or CT.

MRI examination should always include:

Furthermore, in the evaluation of the neurological damage, a significant advantage of MRI is to study neural roots (Fig. 5.19) and plexi, limiting the need for radiography and CT myelography. Root avulsions and lesions of the neural pockets possibly resulting in pseudomeningocele may be shown already in the acute phase, especially by high-resolution 3D T2-weighted “myelographic” sequences. However, when necessary, the complete MR study of a plexus is generally performed on a later stage (generally after 1 month from the trauma) since it requires complete patient’s immobility, absorption of possible posttraumatic hemorrhage, and finally possible surgical therapeutic options (nerve reconstruction) are not performed in the acute phase but generally in 2–3 months from trauma. In addition to “myelographic” images for assessing the integrity of roots and neural pockets, the study should include STIR or fat-suppressed T2-weighted images to rule out or show damage of the plexus elements. Intravenous paramagnetic contrast medium may be useful to demonstrate the damage of the blood–neural barrier in the subacute and chronic phase.

Additionally, MR imaging is superior to CT in the evaluation of bone edema, disc and ligaments injury. Recently, it has been advocated as appropriate to include STIR or fat-suppressed T2-weighted sagittal images of a spinal segment wider than the area of the posttraumatic injury (Figs. 5.11 and 5.16), and possibly of the whole spine. This is to rule out other spinal lesions which, although generally of no great clinical relevance, can be important for overall clinical prognosis and surgical planning [38, 45, 57]. Supraspinous ligament injury may be diagnosed by the discontinuity or nonvisualization of its black stripe of low signal intensity on T1- and/or T2-weighted sagittal images (Figs. 5.8, 5.9, 5.10, and 5.18), i.e., a sign which may be advocated also for flavum ligament injury (Figs. 5.8, 5.10, 5.11, 5.17, and 5.18). Interspinous ligament injury may be diagnosed by high signal intensity on STIR and fat-suppressed T2-weighted images (Figs. 5.9 and 5.17), consistent with hematoma [16], despite this evidence does not mean its certain disruption (Fig. 5.10). Surgical exploration remains the standard reference for the identification of the ligamentous damage. Thus, abnormal T2 signal intensity seen in the capsules or ligaments with normal bone relationships results in an “indeterminate” score in TLICS and SLIC classification systems [52, 53]. Nevertheless, diagnostic imaging aimed to the specific lesional situation seems to facilitate the most appropriate therapeutic choice.

Finally, in the acute phase, certainly the quality of MR studies may be reduced by the presence of cervical collar or spinal longboard (Fig. 5.4).

In the craniocervical junction, occipital condyles, atlas, and axis are provided by a number of ligamentous and articular structures including the transverse ligament of the atlas and the apical ligament (which both form the so-called cruciform ligament), the alar ligaments, the tectorial membrane which blend with the posterior longitudinal ligament, and the atlanto-odontoid, occipitoatlantal, and atlantoaxial joints.

In the subaxial cervical spine and in the thoracolumbar spine, the functional spine unit is formed by an anterior and a posterior portion. The anterior portion includes the two aligned vertebral bodies, the interposed intervertebral disc containing a central hydrated nucleus pulposus and a peripheral annulus fibrosus, and the anterior and posterior longitudinal ligaments. The anterior longitudinal ligament is a strong band of variable thickness and width running the entire length of the spine from the skull base to the sacrum, connecting the anterior vertebral body to the anterior annulus fibrosus. The posterior longitudinal ligament is a strong band, spanning from the body of the axis to the posterior surface of the sacrum, connecting the posterior vertebral body to the posterior annulus fibrosus, forming the anterior wall of the vertebral canal, and superiorly blending with the tectorial membrane. The anterior portion primarily supports axial, or compressive, loading, which is resisted by vertebral bodies and intervertebral disc, which directs forces circumferential towards anterior and posterior ligaments.

The posterior portion includes the vertebral arches, flavum ligaments, facet joints, interspinous and supraspinous ligaments. Flavum ligaments connect the laminae of the adjacent vertebrae and keeps them aligned. Facet joints are posterior portions of the laminae and are the primary elements allowing spinal movements on the basis of their morphology in the cervical, thoracic, and lumbar segments. In the cervical spine, the upward and superomedial inclination of superior articular facets allows free flexion and extension, as well as combination of lateral flexion and rotation. In the thoracic spine, superior articular facets are oriented in the coronal plan, face posteriorly, and are directed a little superolaterally, resulting in free lateral rotation and minimized flexion and extension. In the lumbar spine, superior articular facets are oriented in a sagittal oblique plan and face posteromedially, resulting in a wider range of extension than flexion, while rotation is minimized. Interspinous ligament is a weak and thin membrane connecting the adjacent spinous processes. Supraspinous ligament is a strong cordlike ligament connecting the tips of the spinous processes from C7 to the sacrum. The posterior portion of the functional spinal unit primarily supports movements of the spine, including flexion, extension, and rotation, resisting excessive tensile forces possibly resulting also in translational injuries.

Spinal stability is defined as the ability of the spine to prevent progressive deformity and neurologic injury by maintaining relationships between vertebrae and limiting reciprocal displacements in the different positions, under the action of physiological loading and normal range of movements: this may result only from the whole integrity of vertebrae, intervertebral discs, joints, ligaments, muscles, and neural control [4, 23, 24, 58, 59].

A posttraumatic spinal lesion is considered stable when it can be reduced with external maneuvers and maintained reduced with external means (casts, corsets) till to healing, and unstable when it cannot be reduced by external maneuvers nor it can be maintained reduced by external elements until the healing. Therefore, an unstable posttraumatic spinal lesion requires surgery to restore the stability. However, the differentiation between stable and unstable lesions is still under discussion, and there are no stability or instability criteria universally accepted, even for the specific anatomical and functional characteristics of spinal segments. This resulted in the development of many classification systems guiding clinical and surgical treatment, historically based on anatomic structures and injury mechanisms (axial loading or compression/burst, distraction in flexion or extension, translation/rotation, seat belt injury) determined through analysis of osseous components and their relationships [5, 17, 25, 29, 33, 42, 46, 52, 53].

For instance, for a long time the evaluation of thoracolumbar fractures has been performed on the Denis three-column model classification system (Fig. 5.5), which was based on morphology from compression, burst, seat belt, and fracture dislocation injury mechanisms [5]. Fractures of articular, transverse, and spinous processes, and pars articularis were considered minor fractures. This classification system introduced and highlighted the involvement of the posterior vertebral body and intervertebral disc and the posterior longitudinal ligament, i.e., the “middle column,” whose lesions (Fig. 5.4) were defined to render the spine mechanically unstable and preferably requiring surgery. However, it has been demonstrated that “two-column” “unstable” injuries can also be successfully treated nonsurgically, if the posterior ligamentous complex is intact [29]. Notably, the anatomical models of the columns are not free from criticism since the columns do not represent anatomical or functional biomechanical realities.

A more accurate classification system of fractures of the thoracolumbar spine based on mechanism of injury was then proposed by Magerl et al. in 1994 and also called AO (Arbeitsgemeinschaft für Osteosynthesefragen or Association for Osteosynthesis) classification system [25]. The three main lesional mechanisms give the name to the three main groups of the lesion, i.e., compression, distraction, and translation/rotation. On the basis of fracture location, morphology, osseous or ligamentous disruption, and direction of displacement, each of these three groups is divided into three other and each of the resulting nine subgroups is further divided, for a total of 53 subtypes. The main principle was that fractures represent a continuum of progressively increasing injury severity and instability groups from A to C, resulting in an increasing likelihood of the need for surgery. AO system introduced and highlighted the role of injuries to soft tissues, namely the posterior ligamentous complex. Nevertheless, the complexity of this classification resulted in a certain degree of limited interobserver disagreement, providing poor prognostic data, and thus resulting in a limited use. Additionally, these classification systems did not provide information on the patient’s neurologic status, which is the other basis guiding surgical intervention. Notably, most classification systems lacked an overall assessment of the stability of the spine which has to include a comprehensive assessment of injury mechanism (as expression of immediate mechanical stability), ligamentous injury (as expression of long-term mechanical stability), and neurological status (as expression of clinical stability).

To overcome some of these limitations, in the first decade of 2000s, thoracolumbar injury classification and severity score system, or TLICS [52] and the subaxial cervical spine injury classification system, or SLIC [53] have been proposed for the management and treatment options of fractures of the thoracolumbar and subaxial cervical spine, respectively. These classification systems identified three major characteristics resulting in a weighted score critical to clinical decision-making: (1) injury morphology as determined by the pattern of spinal column disruption on available imaging studies, (2) integrity of the posterior ligamentous complex, or “posterior tensioning band” formed by flavum ligament, facet capsule, interspinous and supraspinous ligaments in the thoracolumbar spine, and of the discoligamentous complex formed by the anterior longitudinal ligament, intervertebral disc, and posterior longitudinal ligament anteriorly, flavum ligament, facet capsule, interspinous and supraspinous ligaments posteriorly in the subaxial cervical spine, and (3) neurologic status of the patient.

More recently, a new comprehensive modified AO spine fracture classification systems have been proposed [54, 55], taking the best of the Magerl, TLICS, and SLIC systems, and scoring fracture morphology, neurologic status, and relevant site- and patient-specific modifiers for therapeutic decisions.