Spine Trauma

Spine trauma is a common indication for diagnostic imaging, and the use of advanced imaging for assessment of spinal injury has become routine at major trauma centers. Injuries of the spine are best understood by considering it as five distinct anatomic regions, each with its own unique anatomy and patterns of injury. These regions consist of the cervicothoracic, low cervical, thoracic, thoracolumbar, and low lumbar segments of the spine, with the majority of injuries occurring in the low cervical and thoracolumbar areas.


Connie Y. Chang and Mini N. Pathria
Spine trauma is a common indication for diagnostic imaging, and the use of advanced imaging for assessment of spinal injury has become routine at major trauma centers. Injuries of the spine are best understood by considering it as five distinct anatomic regions, each with its own unique anatomy and patterns of injury. These regions consist of the cervicothoracic, low cervical, thoracic, thoracolumbar, and low lumbar segments of the spine, with the majority of injuries occurring in the low cervical and thoracolumbar areas.

Craniocervical Junction (CCJ)
The craniocervical junction includes three bones (occipital base, C1, and C2), two joints (atlantooccipital and atlantoaxial), and several extrinsic and intrinsic ligaments, allowing for the delicate balance of flexibility while protecting the cranial blood supply, brainstem, and cranial nerves [1]. Careful description of each injured component and the degree of distraction is important, because these details determine stability and management [1,2]. In this section, we will focus on C2 fractures, which account for 17-20% of cervical spine fractures [3,4]. There are three main C2 fracture types: odontoid fractures, traumatic spondylolysis, and, less commonly, vertebral body/lateral mass fractures [2,3].
Approximately 59% of C2 fractures involve the odontoid process [3,4]. Mortality of C2 fractures in patients 65 years and older is substantial-approximately 15% at 30 days and 34% and 1 year [5]. The most common mechanism is motor vehicle accident, but in older patients even low energy trauma can result in odontoid process fractures [5]. There are three types of odontoid fractures as classified by Anderson and D'Alonzo ( Fig. 13.1) [2,6]. Type I (1-3%) fractures are through the odontoid tip and are likely due to alar ligament avulsion [3,4,6]. Because it is high in the odontoid, type I fractures are considered stable and typically heal with immobilization [3]. Type II (54-60%) fractures are at the junction of the odontoid and the vertebral body, and fractures with >6 mm displacement, comminution, and/or concomitant ligamentous injury have a greater risk of nonunion and likely require surgical management [3,7,8]. Hadley et al. also proposed a type IIA odontoid fracture with additional chip fracture fragments at the dens base, either anteriorly or posteriorly ( Fig. 13.2) [8]. These fractures are unstable and tend toward nonunion [8]. Patients older than 50 years are at greater risk for nonunion [9]. Type III (39-42%) fractures are through the cancellous bone of the vertebral body [4,6]. They are generally stable and heal with halo immobilization [3,4]. Traumatic spondylolisthesis is the second most common C2 fracture (approximately 38%) [1]. This fracture is commonly called the "hangman's fracture," although forensic research suggests that this fracture occurred in less than 10% of judicial hangings; currently it is most commonly due to motor vehicle accidents [10,11]. There are five injury patterns as originally defined by Effendi and later revised by Levine and Starr ( Fig. 13.3) [12]. The degree of distraction and anterior translation should be described, as these determine fracture stability [12]. Type I (65-72%) fractures are the most common, followed by type II (27-28%) ( Fig. 13.4) and type III (1-7%) fractures [3,13]. Type I and type II may appear similar on supine imaging, and upright radiographs may reveal distraction [1,14]. Type IIA has more distraction than translation and therefore a greater degree of kyphosis when compared with type II [1,14]. Neurologic injury is uncommon and only occurs if there is spinal canal narrowing, which may occur in type IA (33%) or type III (60%) injuries [1]. The other fracture types generally result in spinal canal widening [1]. Vertebral body/lateral mass fractures (22%) are the least common, and the vast majority are managed nonoperatively with good result [3]. C2 body fractures are difficult to detect on radiographs, and Pellei described a useful finding called the "fat" C2 sign to improve sensitivity ( Fig. 13.5) [15]. The C2 vertebral body appears "fat" (increased anteroposterior diameter) when there is a displaced vertebral body fracture fragment and suggests that the fracture is unstable requiring further imaging. This sign may be the result of any fracture involving the C2 vertebral body, including a type III dens fracture or an atypical traumatic spondylolysis.

Mid to Lower Cervical
Mid to lower cervical spine (subaxial) injuries represent 65% of cervical spine fractures and are classified based on mechanism of injury: flexion compression, extension compression, vertical compression, flexion-distraction, extensiondistraction, and lateral flexion or rotation [12]. The Subaxial Injury Classification and Scoring (SLIC) system incorporates imaging (CT and MRI) and clinical findings into a single score, placing the patient in nonsurgical (total SLIC a b   Axial CT image of the cervical spine demonstrates bilateral comminuted fractures extending into the vertebral foramina. There was no evidence for vertebral artery injury. This fracture is atypical, but most closely approximates by a type II fracture score ≤3), indeterminate (=4), or surgical (≥5) management categories (Table 13.1) [12]. Each injured level receives a separate score. The abnormality with the highest score is used for the scoring system, i.e., fractures with distraction and translation are scored as translation [16,17].
Familiarity with this scoring system is important for radiologists interpreting these studies, because communication of findings using this terminology enhances communication with the trauma surgeons. Patients with a high SLIC score typically require surgical management to relieve cord compression and stabilize the spine ( Fig. 13.6). Conversely, patients with a low SLIC score can be managed conservatively ( Fig. 13.7).

Key Point
• The Subaxial Injury Classification and Scoring (SLIC) system is helpful for framing evaluation of mid to lower cervical spinal injuries.

Upper Thoracic
The T1-T10 vertebrae are relatively immobile as they are stabilized by a ring formed by the spine, ribs, and sternum so traumatic injuries of this region are less common than at the more mobile cervical and thoracolumbar regions. In young adults, less than 25% of all thoracic fractures affect T1-T10, typically following a fall, motor vehicle accident or seizure [18]. The most common fracture pattern is superior endplate compression resulting in paraspinal swelling, anterior height loss, and disruption of the anterior cortex and subchondral bone, without posterior height loss, retropulsed bone, or malalignment. Mild height loss alone lacks specificity as it can be physiologic or due to Scheuermann disease, which is associated with disk height loss, Schmorl nodes, and kyphosis [19]. Impacted subchondral trabecular bone is more specific, appearing as a transverse zone of sclerosis paralleling the endplate that becomes more apparent as the fracture heals. Mild compression fractures are stable, but those with greater than 40% height loss can result in delayed kyphotic deformity, particularly if there are multiple contiguous fractures [20]. however, there is also >3.5 mm anterolisthesis, which is <50% of the caudal vertebral body AP dimension, resulting in a SLIC morphology score of 4. The discoligamentous complex is disrupted, consistent with a SLIC score of 2. The total SLIC score is 10, which would warrant surgical management for the fracture There is compression of the vertebral body, consistent with a SLIC morphology score of 1. The total SLIC score is low and the patient was successfully treated with conservative management radiographs. Osteoporotic thoracic fractures are common; 18% of white women older than 50 and 78% of white women older than 90 years have at least one thoracic compression fracture, typically in conjunction with additional fractures in the lumbar region [21]. Bone fragility allows the fracture to propagate easily to the posterior vertebral body margin, resulting in greater height loss and retropulsion of bone into the canal. In elderly patients, distinguishing osteoporotic fractures from pathologic fractures can be challenging. Findings sug-gesting underlying neoplasia include isolated fractures above T7, preferential posterior height loss or bulging of the posterior cortex, cortical erosion of the vertebral body or posterior elements, soft tissue mass, and diffuse replacement of the vertebral body fat signal, whereas a simple transverse fracture line with band-like partial marrow replacement limited to the upper or lower half of the vertebral body and the presence of a linear cleft of fluid or gas favor a benign process [22] (Fig. 13.8). MR techniques that identify regions of restricted diffusion within neoplastic tissue and phase imaga b ing to identify microscopic fat within benign lesions are useful in equivocal cases though some fractures remain indeterminate, requiring biopsy [23].
Severe upper thoracic injuries such as burst fractures with retropulsed bone, anterior and posterior distraction injuries, and fracture-dislocation are uncommon. Fracturedislocation of the upper thoracic spine is the result of combined hyperflexion, axial loading, and rotary/shear forces resulting in extensive ligament disruption, complex fractures, and spinal malalignment including translation, rotation, and telescoping of vertebrae [23] (Fig. 13.9). In such injuries, the disproportionately small ratio of the spinal canal to the cord in the upper thoracic region leads to a high risk of neurologic deficit. Soft tissue hemorrhage and associated visceral and mediastinal injuries are common [18]. CT and MR are needed to fully characterize a b

Thoracolumbar
The thoracolumbar region is commonly injured, representing the second most common site of spinal trauma following the lower cervical spine. Modern classification systems of spinal injury are based on systems initially developed to organize thoracolumbar injuries according to injury mechanism, using fracture morphology and degree of displacement to assess stability and plan management. The initial system widely used was the Denis classification that divided the spine into anterior, middle, and posterior columns, emphasizing the role of the middle column (posterior vertebral margin, posterior longitudinal ligament, and posterior annulus) in maintaining stability [24]. Denis classified thoracolumbar injuries into (1) compression fracture limited to the anterior column; (2) burst fracture involving anterior and middle columns; (3) seat belt injury resulting from distraction of the middle and posterior columns from distraction; and (4) fracture-dislocation with disruption of all three columns. This classification was based on radiographs and did not account for many spinal injuries, particularly those where the anterior spine was compressed while the posterior ligaments failed by distraction, a pattern well appreciated on MR imaging. Current classification systems have expanded Denis' system to offer a more comprehensive classification and account for more injury patterns and also include clinical parameters. Currently, the most widely used thoracolumbar injury classification is based on combining features of the AO-Magerl classification (Arbeitsgemeinschaft für Osteosynthesefragen) and TLICS (Thoracolumbar Injury Classification and Severity Score) system [16,20]. The AO/TLICS system, based on a consensus of international spine surgeons, classifies fracture morphology into three main patterns: type A (compression), type B (tension band disruption, either anterior or posterior), and type C (displacement/translation) with several subtypes in the first two categories. The grading of morphology relies on accurate assessment of both bone and ligament injury and emphasizes the utility of CT and MRI for assessment of thoracolumbar trauma [25].
The fracture morphology score is combined with a grading of neurologic status and a description of patient-specific modifiers that affect the likelihood of surgery to help select management [16]. This classification has similar considerations as the SLIC grading system of cervical trauma previously discussed.

Type A: Compression Injuries
The most common injury mechanism is compression which produces a range of fracture morphologies that include superior and inferior endplate impaction, anterior wedging of varying severity, burst fractures, and sagittal splitting of the vertebral body. Similar to the remainder of the spine, mild compression fractures result in anterior height loss, buckling of the cortex, and endplate comminution producing bandlike sclerosis adjacent to the fractured endplate. On CT, these appear as an arc of irregular bony fragments displaced circumferentially at the level of the endplate. Posterior vertebral and intervertebral disk height are preserved and there is no listhesis. Compression fractures with greater than 40% height loss, particularly in the setting of multiple contiguous fractures and posterior ligament sprain may require prolonged bracing [26]. Severe compression fractures showing with greater than 70% height loss may require posterior stabilization to avoid kyphotic deformity. Unlike simple compression fractures, burst fractures involve the posterior vertebral body margin, leading to posterior vertebral height loss and retropulsed bone in the spinal canal. The thoracolumbar region is the most common site of spinal burst fractures, and such injuries make up 16% of all spinal injuries encountered at a trauma center. CT scanning is the most efficient method for characterizing the fracture, identifying associated posterior element fractures and evaluating bone encroaching on the spinal canal ( Fig. 13.10).

Type B: Distraction (Tension Band) Injuries
The vast majority of distraction injuries of the thoracolumbar spine results from flexion with the resulting tensile force, leading to purely osseous, purely ligamentous, or combined bony and soft tissue injury starting at the posterior spine allowing separation between the posterior elements, followed by anterior soft tissue injury or vertebral fracture. The classic horizontally oriented Chance fracture is one example of a distraction injury, but there is a broad spectrum of distraction injury patterns depending on whether the injury is primarily ligamentous or osseous and whether distraction affects the entire spine or only the posterior elements. Distraction injuries are associated with variable amounts of

Key Point
• The AO/TLICS classification of thoracolumbar injuries is based on fracture morphology as defined by imaging, categorizing fractures into those caused by compression, distraction, or translation.
splaying of the posterior elements, which can be overlooked on radiographs and CT, particularly if the patient is recumbent [27]. In practice, many posterior tension band injuries with vertebral body fractures are easily confused for simple compression or burst fractures without MR imaging, which should be obtained whenever posterior ligament injury is suspected ( Fig. 13.11). Anterior tension band injuries caused by hyperextension are far less common. The typical injury pattern is a horizontal fracture through the vertebral body or through an ossified disk in an elderly patient with underlying degenerative spinal fusion, leading to increased vertebral or disk height and lordosis [28].

Type C: Displacement/Dislocation
The most severe pattern of injury consists of displacement injuries with translation and/or rotation due to disruption of all the spinal ligaments, typically in association with fractures at both the anterior and posterior vertebra. Rib fractures and costotransverse dislocations often accompany these injuries.
Thoracolumbar displacement/dislocation injuries are associated with a high rate of neurologic deficit, with 50-90% of patients developing a permanent neurologic deficit.

Lower Lumbar
Pars interarticularis fracture or spondylolysis is a stress fracture of the bony arch connecting the upper and lower facet joints and occurs primarily at the L5 (85-95%) and L4 (5-15%) levels [29,30]. The prevalence is approximately 6%, and many are asymptomatic, but spondylolysis can cause pain in athletes with high lower back stress (football, wrestling, dancing, weight lifting), particularly in the adolescent and preadolescent population [31,32]. Diagnosis on radiographs is best made on the oblique view, but radiographs have low sensitivity for stress injury and nondisplaced stress fractures (Fig. 13.12) [30,33]. Flexion and extension views can detect motion and instability in the case of spondylolisthesis, which occurs in 50-81% of patients with spondylolysis [29,31,33]. A low threshold for obtaining a CT or MRI in patients with a suspicious clinical history and physical examination is recommended, because early detection and appropriate treatment (primarily rest and pain management) is important to prevent progression and more aggressive intervention [29]. CT has the highest sensitivity for fracture detection, while MRI has the advantage of detecting edema in early-stage injury (Fig. 13.13) [29]. Most patients are successfully managed conservatively, with surgery reserved for the 9-15% of cases that remain symptomatic after conservative care [29]. Because the condition can be asymptomatic, diagnostic steroid and anesthetic injection can be helpful to confirm the spondylolysis as the source of the patient's pain prior to surgery [34].

Concluding Remarks
Diagnostic imaging plays a critical role in identifying and classifying spinal injury. Understanding the unique features of each spinal segment and relevant classification systems can help the radiologist both with injury detection and with generating clinically relevant reports to help guide management.