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The Traumatized Vertebral Spine Reloaded: Injury Mechanisms and their Radiologic Patterns Claudia Schueller-Weidekamm, MD, PhD, MBA2
1 Department of Radiology, Spital Bülach, Bülach, Switzerland 2 Section Head of Functional and Morphological Musculoskeletal
Radiology, Division of Neuroradiology and Musculoskeletal Radiology, Department of Biomedical Imaging und Image-Guided Therapy, Medical University of Vienna, Vienna General Hospital, Vienna, Austria
Address for correspondence Gerd Schueller, MD, MBA, Department of Radiology, Spital Bülach, Spitalstrasse 24, 8180 Bülach, Switzerland (e-mail: offi[email protected]).
Semin Musculoskelet Radiol 2014;18:240–245.
Abstract
Keywords
► ► ► ► ► ►
trauma spine injury diagnosis CT MRI
The ideal classification of spinal trauma does not yet exist, primarily because the implementation of morphological, biomechanical, and clinical parameters in a single nomenclature is a difficult task. For radiologists and surgeons, who are partners in trauma teams, only a few classifications of injury patterns have been shown to be useful enough to provide rapid and stable therapy decisions in daily practice. From a didactic point of view, however, simplifications of injury mechanisms are of help to become aware of the most important radiologic injury patterns of vertebral trauma. The members of trauma teams should be aware of the strengths and limitations of existing descriptions of imaging features when reporting trauma to the spine. These are discussed in this article.
The spine is most often injured in motor vehicle accidents, after falls from heights, and during sports activities. Especially in motor vehicle accidents, many predicting factors come together, such as young men are predominantly injured; alcohol consumption is predictive, as is the lack of fastened seat belts; and severe vertebral spine trauma has a positive correlation with high-speed impacts.1 The cervical spine is damaged in more than the half the cases. Another prominent point of injury is observed at the thoracolumbar junction.1 In 75% of vertebral trauma, multiply and severely injured patients are encountered; in these patients in particular, cervical spine injury is frequent. A second peak of vertebral trauma occurs among the elderly who experience longstanding degenerative disease that makes the spine more disposed to sustain an acute trauma (►Fig. 1). Vertebral spine injury has been discussed controversially for as long as there have been attempts to classify it. A classification of vertebral trauma, to be widely accepted, should be simple and reproducible. It should describe several factors, most of all morphological, biomechanical, and clinical parameters. However, such an ideal classification does not, as yet, exist. One of the best known is the classification by
Issue Theme Spine; Guest Editor, Mara Epermane, MD
Magerl et al.2 This classification was also adopted by the Swiss-based Arbeitsgemeinschaft für Osteosynthesefragen (AO). It explains vertebral spine injury with the help of a two-column model. Its nomenclature comprises three principal injury mechanisms: compression, distraction, and combined disorders including rotational fracture. The intent of the Magerl classification was to classify thoracolumbar vertebral trauma. However, in daily practice, it is used to classify cervical trauma as well.3 From a trauma surgeon’s point of view, most descriptions used are based on the Denis model.4 Stability and instability of traumatic vertebral injuries is explained by the help of a three-column model. The anterior column is composed of the anterior longitudinal ligament and the anterior two thirds of the vertebral bodies, the cartilaginous end plates, and the intervertebral disks. The middle column is composed of the posterior third of these structures and of the posterior ligament. The posterior column contains all the posterior bony and ligamentous elements.5 If the anterior or posterior column is disrupted, the other columns may provide sufficient stability to prevent spinal cord injury. If two columns are disrupted, the spine may move as two separate units (►Fig. 2). As a result, the ability of the vertebral column
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1375567. ISSN 1089-7860.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Gerd Schueller, MD, MBA1
Fig. 1 Flexion-compression fracture after a moderate trauma in a 67-year-old man. Note the preexisting spondylophyte on the anterior vertebral edge.
under physiologic conditions to maintain alignment and protect the neural structures from damage4 would be decreased. The Denis classification comprises four injury patterns: compression (anterior column), burst (anterior and middle columns), flexion-distraction (anterior and posterior columns; middle column is the center of rotation), and fracture-dislocation (all columns). From a clinical point of view, a minority of compression fractures, some burst fractures, most flexion-distraction fractures, and all fracture-dislocation injuries are unstable injuries. From a radiologic point of view, however, the stability or instability of vertebral spine fractures are not unequivocally delineated in many cases, especially in burst fractures. However, there is broad consensus about what constitutes stability, based on three imaging features: a spinal canal
Fig. 2 Fracture of C6 after a blunt cervical trauma. Both the middle (arrow) and posterior columns are fractured. According to the Denis model,4 it is an unstable fracture.
Schueller, Schueller-Weidekamm
stenosis < 50% in neurologically unremarkable patients, a reduction in height of the anterior vertebral edge < 50%, and a focal kyphosis 30 degrees.6 Among the relative imaging features that constitute instability are a dislocation of a vertebral body, an increased interlaminar and/or interspinous distance, wide facet joints, an increased vertical and horizontal distance of the pedicles, and a discontinuous posterior edge of a vertebral body. Similar to thoracic or head trauma, vertebral spine injury has predictable patterns. The radiologic findings seen after specific injuries are stereotypical. It is well recognized that, on the basis of a specific trauma mechanism, characteristic findings are observed. The described injury patterns more or less describe simple stress factors responsible for a specific injury. However, what is closer to reality is that a wide spectrum of stress factors is responsible for each injury mechanism. Thus it is the combination of all forces that results in the main traumatizing vector. In relation to the instantaneous axis of rotation of one vertebra to another, this vector causes different injuries. For example, the instantaneous axis of rotation of the L1–L2 segment is considered in the anterocentral portion of L1. If the traumatizing vector is effective anteriorly to this axis, then a flexion mechanism is the result (►Fig. 3). On the contrary, if the vector is effective posteriorly, then an extension injury will occur (see later). Thus the instantaneous axis of rotation has biomechanical implications on the deformity of the vertebral spine, regardless the level of an injury.7
Flexion and Compression, Burst, Extension, Fracture-Dislocation, and Luxation Injuries With moderate flexion and compression, a longitudinal pull is exerted on the anterior ligament complex. Because this is a very strong ligament, it usually remains intact, and, as a consequence, the anterior vertebral body has to bear most of the force, resulting in a wedge compression fracture. According to the Denis model,4 the anterior column is injured, without disruption of the posterior elements. These fractures are considered stable. The major radiologic feature is the diminished height of the anterior edge of a vertebral body. At the level of the cervical spine, the C5–C7 segments are mostly involved. However, in many cases, not only one segment is injured. Consequently, the entire spine should be thoroughly investigated in patients with a proven compression fracture (►Fig. 4). When a flexion mechanism is combined with a severe axial compression at the cervical spine, flexion teardrop fractures occur. In some classifications, these are described as a variant of burst fractures. They are typically caused by diving into shallow water or comparable accidents. The anteroinferior aspect of the vertebral body is fractured. This fragment is displaced anteriorly and resembles a teardrop. For this fragment to be produced, significant posterior ligamentous disruption must occur. The injury involves all three columns, rendering the injury highly unstable. This is often accompanied by spinal cord injury. A type I fracture is described as deterioration of the anterior vertebral edge, in Seminars in Musculoskeletal Radiology
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Traumatized Vertebral Spine Revisited
Traumatized Vertebral Spine Revisited
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Fig. 3 (a) The instantaneous axis of rotation of the L1–L2 segment is marked in the anterocentral portion of L1 (dotted line). (b) If the traumatizing vector is effective anteriorly to this axis (arrow), a (c) flexion mechanism occurs (arrow).
combination with an anterior dislocation and a rupture of the anterior longitudinal ligament. A type II fracture is described as a teardrop fragment with discontinuity of the posterior vertebral edge and distended facet joints, as well as a widened interlaminar space. At the level of the thoracolumbar junction, this injury mechanism causes the Chance fracture.8 The vertebra is horizontally ruptured into two parts. In particular, the levels T10– L2 are involved. Anteriorly, only a discrete compression is seen. It is combined with a severe distraction of the posterior column. This fracture is unstable. In general, in high-speed injuries, the combination of an axial load and a flexion causes the upper body to bend forward while the lower body is fixed. Chance fractures are associated with mesenteric and bowel injury in about half of these cases. The Smith fracture is a variant of a horizontal flexion fracture. The disruption of the posterior spinal elements occurs through the interspinous ligaments while there is no difference in the remaining fracture patterns compared with the Chance fracture. A burst fracture occurs when a severe compressive force is transmitted to the spine axially and a disk fractures into its adjacent lower vertebral body, causing a disruption of this vertebral body (►Fig. 5). This injury mechanism leads to the disruption of the anterior and middle columns. The posterior column has variable degrees of injury. Radiologically, fragments are seen that narrow the spinal canal and compress the myelon. Burst fractures commonly involve the thoracic and the lumbar spine. At the upper cervical spine, a burst mechanism most often causes a Jefferson fracture.9 This is a synonym for a fracture of the atlas ring. The axial force is transmitted through the occipital condyles. It displaces the masses laterally and causes fractures of the anterior and posterior arches. The reason for the instability of the Jefferson fracture is the avulsion of the transverse ligament. Originally, a four-fragment fracture was described and is classified as a Gehweiler type III fracture.10 Seminars in Musculoskeletal Radiology
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However, three fragment fractures occur as well. In general, fractures of the atlas were classified by Gehweiler into five types. Type I and II fractures are isolated fractures of the anterior or posterior arches. These fractures are also referred to as nutcracker fractures because they are a result of an anterior distraction and posterior compression between the occipital condyles and the axis. Type IV and V fractures are isolated stable fractures of the lateral mass of the axis or of a transverse process, respectively. In particular, these fractures can lead to the dissection of the vertebral artery. Thus, in many trauma centers, cervical injuries are an indication for computed tomography (CT) angiography of the supraaortic branches. However, this technique is not based on evidence.11,12 If the traumatizing vector is effective dorsally in relation to the instantaneous axis of rotation, an extension mechanism occurs and leads to the distraction (i.e., elongation of the anterior column), according to the Denis model.4 Hyperextension lesions are rare. They are defined by an osseous and/or ligamentous disruption of all columns, and they are highly unstable. Radiologically, at the anterior column, a bony disruption is most often visible. More importantly, indirect signs of this injury are a retrolisthesis, as well as a widening of the intervertebral space and the interspinous distance. These findings occur due to severe soft tissue damage to the intervertebral disks and to the posterior vertebral elements. They are suitably diagnosed by magnetic resonance imaging (MRI). During motor vehicle accidents in particular, the injury mechanism includes the likelihood that the driver’s thorax, without the seat belt fastened, is pushed toward the steering wheel, and the face is slammed down on the windshield. At the level of the upper cervical spine, this injury mechanism causes traumatic spondylolysis of the axis, the Hangman fracture.13 The fracture involves the interarticulare parts bilaterally and/or the pedicles, the body, and the facets as well as the transverse processes. Also, the intervertebral disk C2–C3 is ruptured. The fractured pedicles, however, allow
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Fig. 5 Burst fracture of L1 with minor involvement of the posterior vertebral edge (arrow).
Fracture-dislocation, which is among the types of injury of the Denis classification,4 is caused by severe shear and rotational forces. Most often, these are combined with a substantial compression (e.g., these fractures are seen after a severe impact onto the patient́ s back while the lower body is rotated to one side). This occurs when passengers are ejected from a car or in comparable accidents. This injury includes vertebral disruption and comminution. It is associated with substantial neurologic symptoms. Fracture-dislocation injuries are associated with unilateral or bilateral facet joint luxations. A unilateral luxation is caused by the combination of rotation and flexion, whereas a bilateral luxation frequently occurs after rotation and compression.15 The bilateral luxation represents a highly unstable condition. The vertebral body dislocation in the injured segment is at least 50%.The articular malalignment is best visible on axial and sagittal images. It is referred to as the “naked” facet sign.16 Another radiologically useful sign is the “reversed hamburger bun” sign.17 It reflects a convex rather than a normal concave appearance of the articular surface. Most often, the thoracolumbar junction is involved because the physiologic biomechanical reduction of its vertebral joints makes them prone to a rotational injury.
Fig. 4 Multiple fractures (arrows) in a 53-year-old man after a fall from a height. Note the involvement of posterior vertebral elements in T9 and T10 (arrowheads) and of the middle column in L1 (asterisks).
decompression of the spinal canal. Thus neurologic symptoms do not appear as early because there is a combination of bilaterally blocked facet joints. A rotational component may cause an asymmetry of the fracture.14
Diagnostic Algorithm In the evaluation of patients with suspected vertebral spine trauma, several questions remain controversial: which patients need imaging, how much imaging is necessary, and what kind of imaging should be performed? Concerns about cost and radiation exposure require careful patient selection. Regarding cervical spine imaging, the most significant studies are the National Emergency Seminars in Musculoskeletal Radiology
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Traumatized Vertebral Spine Revisited
Traumatized Vertebral Spine Revisited
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X-radiography Utilization Study (NEXUS)18 and the Canadian Cervical Spine Prediction Rule Study (CCSPR).19 Both studies, together comprising > 43,000 patients, revealed comparable high sensitivities for identifying patients at risk for significant spine injury. This means that patients who meet the dedicated low-risk criteria that have been established by these studies (i.e., no midline cervical tenderness, no focal neurologic deficits, no intoxication or indication of brain injury, no painful distracting injuries, normal alertness) do not need imaging.18,19 However, adults who do not fulfill these low-risk criteria do require imaging. In a meta-analysis of seven studies, the pooled sensitivity of radiography for detecting patients with cervical spine injury was as low as 52%; the combined sensitivity of CT was 98%.20 Thus CT, and not radiography, should be the primary screening study for suspected cervical spine injury. Radiographic studies should be performed only when CT is not readily available and should not be considered a substitute for CT. The literature does not define a minimum section thickness, maximum voxel dimensions, or other technical factors for these images. However, we recommend a collimation of at least 1.5 mm. Three plane reformations should be performed. Flexion and extension views are not considered cost effective in cervical spine imaging in the trauma setting.21 However, flexion and extension imaging of the cervical spine could be useful in evaluating potential ligamentous injury in patients after normal or inconclusive MRI findings. It is generally accepted that soft tissue injuries are quite common after a significant spine trauma, and many of these lesions do not lead to mechanical instability. Unfortunately, MRI is not an unequivocal troubleshooter because, on the one hand, it potentially misses significant lesions, and, on the other, it also detects many clinically insignificant lesions. To date, there is not sufficient evidence to establish the reliability of the NEXUS criteria in younger children or to recommend whether radiography or CT should be the initial imaging study. In their study, Oman and coworkers enrolled 1,666 children with suspected spinal injury.22 The authors retrospectively applied the NEXUS criteria and found them to be reliable in children. The recommended protocol for cervical spine clearance included radiography as the first-line imaging study; CT and MRI are reserved for patients with inconclusive findings. Radiography is supposed to be of sufficiently high accuracy in imaging the pediatric population. One of the reasons may be that children experience cervical spine injury in a slightly different manner than adults. Children most often have injuries at the atlantooccipital and atlantodental segments, respectively. These are the regions where pediatric radiographs perform best. Thoracolumbar spine imaging is indicated if any of the following are present: high-energy trauma; back pain, or midline tenderness; local signs of thoracolumbar injury; abnormal neurologic signs; cervical spine fracture; Glasgow Coma Scale < 15; major distracting injury according to the referring physician; and alcohol or drug intoxication.23 The literature indicates no clear recommendation about which imaging modality should be used. However, these indications Seminars in Musculoskeletal Radiology
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Fig. 6 Non-recent type I lesion according to Bondurant et al 28: intramedullar bleeding shows a hypointense rim due to blood products nine months after trauma. Distal atrophy of the spinal cord is a result of the Wallerian degeneration in a chronic injury (arrow).
may also be considered as indications for CT imaging of the thorax and the abdomen. Imaging patients with neurologic symptoms is a matter for MRI. According to the criteria established by the American College of Roentgenology, MRI should be performed in patients whose neurologic status cannot be fully evaluated within 48 hours of injury including those in whom CT is normal.24 There is no clear evidence that MRI performed > 48 hours after an injury is of lower sensitivity than an acute MRI. Instead, the recommendation to perform MRI within 48 hours is due to concerns about keeping patients in collars unnecessarily for a prolonged period of time. Due to its high elasticity, the myelon of children is prone to severe trauma. However, symptoms in children often occur without correlation with MRI images: spinal cord injury without radiographic abnormality.25 Another challenge of spinal cord injuries is among the elderly, at least in part because of a preexisting narrowing of the spinal canal.26 The American Spinal Injury Association score is considered the reference in neurologic spine imaging, describing lesions from A (no function below the level of the injury) to E (normal function).27 From a radiologic point of view, medullary lesions are suitably discriminated after Bondurant et al.28 Findings are graded into three types, according to the presence of edema and cord swelling, blood products, or both (►Fig. 6). Therefore, these radiologic findings can be considered prognostic markers, which have been described previously.24
Conclusion Key variables, such as the delineation of instability, have implications for patients’ treatment and outcome, and they
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12 Malhotra AK, Camacho M, Ivatury RR, et al. Computed tomograph-
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18
Conflict of Interest The authors have nothing to disclose. 19
References
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1 Schueller G. Who is who revisited: spinal trauma [in German].
Radiologe 2010;50(12):1084–1095 2 Magerl F, Aebi M, Gertzbein SD, Harms J, Nazarian S. A compre-
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hensive classification of thoracic and lumbar injuries. Eur Spine J 1994;3(4):184–201 Reinhold M, Blauth M, Rosiek R, Knop C. Lower cervical spine trauma: classification and operative treatment [in German]. Unfallchirurg 2006;109(6):471–480; quiz 481–483 Kim CW, Perry A, Garfin SR. Spinal instability: the orthopedic approach. Semin Musculoskelet Radiol 2005;9(1):77–87 Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983; 8(8):817–831 Willén J, Anderson J, Toomoka K, Singer K. The natural history of burst fractures at the thoracolumbar junction. J Spinal Disord 1990;3(1):39–46 Daffner RH, Deeb ZL, Rothfus WE. “Fingerprints” of vertebral trauma—a unifying concept based on mechanisms. Skeletal Radiol 1986;15(7):518–525 Chance GQ. Note on a type of flexion fracture of the spine. Br J Radiol 1948;21(249):452 Han SY, Witten DM, Mussleman JP. Jefferson fracture of the atlas. Report of six cases. J Neurosurg 1976;44(3):368–371 Gehweiler JA, Duff DE, Martinez S, Miller MD, Clark WM. Fractures of the atlas vertebra. Skeletal Radiol 1976;1:97–102 Langner S, Fleck S, Kirsch M, Petrik M, Hosten N. Whole-body CT trauma imaging with adapted and optimized CT angiography of the craniocervical vessels: do we need an extra screening examination? AJNR Am J Neuroradiol 2008;29(10):1902–1907
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ic angiography for the diagnosis of blunt carotid/vertebral artery injury: a note of caution. Ann Surg 2007;246(4):632–642; discussion 642–643 Effendi B, Roy D, Cornish B, Dussault RG, Laurin CA. Fractures of the ring of the axis. A classification based on the analysis of 131 cases. J Bone Joint Surg Br 1981;63-B(3):319–327 Samaha C, Lazennec JY, Laporte C, Saillant G. Hangman’s fracture: the relationship between asymmetry and instability. J Bone Joint Surg Br 2000;82(7):1046–1052 Palmieri F, Cassar-Pullicino VN, Dell’Atti C, et al. Uncovertebral joint injury in cervical facet dislocation: the headphones sign. Eur Radiol 2006;16(6):1312–1315 O’Callaghan JP, Ullrich CG, Yuan HA, Kieffer SA. CT of facet distraction in flexion injuries of the thoracolumbar spine: the “naked” facet. AJR Am J Roentgenol 1980;134(3):563–568 Daffner SD, Daffner RH. Computed tomography diagnosis of facet dislocations: the “hamburger bun” and “reverse hamburger bun” signs. J Emerg Med 2002;23(4):387–394 Hoffman JR, Mower WR, Wolfson AB, Todd KH, Zucker MI; National Emergency X-Radiography Utilization Study Group. Validity of a set of clinical criteria to rule out injury to the cervical spine in patients with blunt trauma. N Engl J Med 2000;343(2):94–99 Stiell IG, Wells GA, Vandemheen KL, et al. The Canadian C-spine rule for radiography in alert and stable trauma patients. JAMA 2001;286(15):1841–1848 Holmes JF, Akkinepalli R. Computed tomography versus plain radiography to screen for cervical spine injury: a meta-analysis. J Trauma 2005;58(5):902–905 Anglen J, Metzler M, Bunn P, Griffiths H. Flexion and extension views are not cost-effective in a cervical spine clearance protocol for obtunded trauma patients. J Trauma 2002;52(1):54–59 Oman JA, Cooper RJ, Holmes JF, et al; NEXUS II Investigators. Performance of a decision rule to predict need for computed tomography among children with blunt head trauma. Pediatrics 2006;117:e238–e246 Hsu JM, Joseph T, Ellis AM. Thoracolumbar fracture in blunt trauma patients: guidelines for diagnosis and imaging. Injury 2003;34(6):426–433 Schüller-Weidekamm C. Cervical spine injury. . Diagnosis, prognosis and management [in German]. Radiologe 2008;48(5): 480–487 Pang D, Wilberger JE Jr. Spinal cord injury without radiographic abnormalities in children. J Neurosurg 1982;57(1):114–129 Hendey GW, Wolfson AB, Mower WR, Hoffman JR; National Emergency X-Radiography Utilization Study Group. Spinal cord injury without radiographic abnormality: results of the National Emergency X-Radiography Utilization Study in blunt cervical trauma. J Trauma 2002;53(1):1–4 Maynard FM Jr, Bracken MB, Creasey G, et al; American Spinal Injury Association. International Standards for Neurological and Functional Classification of Spinal Cord Injury. Spinal Cord 1997; 35(5):266–274 Bondurant FJ, Cotler HB, Kulkarni MV, McArdle CB, Harris JH Jr. Acute spinal cord injury. A study using physical examination and magnetic resonance imaging. Spine 1990;15(3):161–168
Seminars in Musculoskeletal Radiology
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should not be discussed from a radiologic point of view only. Rather, the collaboration of radiologists with all other members of the trauma team is crucially important. A reasonable classification of vertebral spine trauma comprises criteria that include the injury mechanism as well as morphological and clinical findings. Such a classification represents a unique language between radiologists and clinicians. However, the ideal classification of spine trauma does not yet exist. Instead, we face many synonyms and eponyms (e.g., Jefferson fracture, Hangman fracture). They provide a high degree of specific information and should be fully understood by trauma radiologists because they contribute to interdisciplinary collaboration and communication. By relying on these few essentials, radiologists will serve as effective partners in the management of patients with vertebral spinal trauma.
Schueller, Schueller-Weidekamm
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The Traumatized Vertebral Spine Reloaded: Injury Mechanisms and their Radiologic Patterns Claudia Schueller-Weidekamm, MD, PhD, MBA2
1 Department of Radiology, Spital Bülach, Bülach, Switzerland 2 Section Head of Functional and Morphological Musculoskeletal
Radiology, Division of Neuroradiology and Musculoskeletal Radiology, Department of Biomedical Imaging und Image-Guided Therapy, Medical University of Vienna, Vienna General Hospital, Vienna, Austria
Address for correspondence Gerd Schueller, MD, MBA, Department of Radiology, Spital Bülach, Spitalstrasse 24, 8180 Bülach, Switzerland (e-mail: offi[email protected]).
Semin Musculoskelet Radiol 2014;18:240–245.
Abstract
Keywords
► ► ► ► ► ►
trauma spine injury diagnosis CT MRI
The ideal classification of spinal trauma does not yet exist, primarily because the implementation of morphological, biomechanical, and clinical parameters in a single nomenclature is a difficult task. For radiologists and surgeons, who are partners in trauma teams, only a few classifications of injury patterns have been shown to be useful enough to provide rapid and stable therapy decisions in daily practice. From a didactic point of view, however, simplifications of injury mechanisms are of help to become aware of the most important radiologic injury patterns of vertebral trauma. The members of trauma teams should be aware of the strengths and limitations of existing descriptions of imaging features when reporting trauma to the spine. These are discussed in this article.
The spine is most often injured in motor vehicle accidents, after falls from heights, and during sports activities. Especially in motor vehicle accidents, many predicting factors come together, such as young men are predominantly injured; alcohol consumption is predictive, as is the lack of fastened seat belts; and severe vertebral spine trauma has a positive correlation with high-speed impacts.1 The cervical spine is damaged in more than the half the cases. Another prominent point of injury is observed at the thoracolumbar junction.1 In 75% of vertebral trauma, multiply and severely injured patients are encountered; in these patients in particular, cervical spine injury is frequent. A second peak of vertebral trauma occurs among the elderly who experience longstanding degenerative disease that makes the spine more disposed to sustain an acute trauma (►Fig. 1). Vertebral spine injury has been discussed controversially for as long as there have been attempts to classify it. A classification of vertebral trauma, to be widely accepted, should be simple and reproducible. It should describe several factors, most of all morphological, biomechanical, and clinical parameters. However, such an ideal classification does not, as yet, exist. One of the best known is the classification by
Issue Theme Spine; Guest Editor, Mara Epermane, MD
Magerl et al.2 This classification was also adopted by the Swiss-based Arbeitsgemeinschaft für Osteosynthesefragen (AO). It explains vertebral spine injury with the help of a two-column model. Its nomenclature comprises three principal injury mechanisms: compression, distraction, and combined disorders including rotational fracture. The intent of the Magerl classification was to classify thoracolumbar vertebral trauma. However, in daily practice, it is used to classify cervical trauma as well.3 From a trauma surgeon’s point of view, most descriptions used are based on the Denis model.4 Stability and instability of traumatic vertebral injuries is explained by the help of a three-column model. The anterior column is composed of the anterior longitudinal ligament and the anterior two thirds of the vertebral bodies, the cartilaginous end plates, and the intervertebral disks. The middle column is composed of the posterior third of these structures and of the posterior ligament. The posterior column contains all the posterior bony and ligamentous elements.5 If the anterior or posterior column is disrupted, the other columns may provide sufficient stability to prevent spinal cord injury. If two columns are disrupted, the spine may move as two separate units (►Fig. 2). As a result, the ability of the vertebral column
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1375567. ISSN 1089-7860.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Gerd Schueller, MD, MBA1
Fig. 1 Flexion-compression fracture after a moderate trauma in a 67-year-old man. Note the preexisting spondylophyte on the anterior vertebral edge.
under physiologic conditions to maintain alignment and protect the neural structures from damage4 would be decreased. The Denis classification comprises four injury patterns: compression (anterior column), burst (anterior and middle columns), flexion-distraction (anterior and posterior columns; middle column is the center of rotation), and fracture-dislocation (all columns). From a clinical point of view, a minority of compression fractures, some burst fractures, most flexion-distraction fractures, and all fracture-dislocation injuries are unstable injuries. From a radiologic point of view, however, the stability or instability of vertebral spine fractures are not unequivocally delineated in many cases, especially in burst fractures. However, there is broad consensus about what constitutes stability, based on three imaging features: a spinal canal
Fig. 2 Fracture of C6 after a blunt cervical trauma. Both the middle (arrow) and posterior columns are fractured. According to the Denis model,4 it is an unstable fracture.
Schueller, Schueller-Weidekamm
stenosis < 50% in neurologically unremarkable patients, a reduction in height of the anterior vertebral edge < 50%, and a focal kyphosis 30 degrees.6 Among the relative imaging features that constitute instability are a dislocation of a vertebral body, an increased interlaminar and/or interspinous distance, wide facet joints, an increased vertical and horizontal distance of the pedicles, and a discontinuous posterior edge of a vertebral body. Similar to thoracic or head trauma, vertebral spine injury has predictable patterns. The radiologic findings seen after specific injuries are stereotypical. It is well recognized that, on the basis of a specific trauma mechanism, characteristic findings are observed. The described injury patterns more or less describe simple stress factors responsible for a specific injury. However, what is closer to reality is that a wide spectrum of stress factors is responsible for each injury mechanism. Thus it is the combination of all forces that results in the main traumatizing vector. In relation to the instantaneous axis of rotation of one vertebra to another, this vector causes different injuries. For example, the instantaneous axis of rotation of the L1–L2 segment is considered in the anterocentral portion of L1. If the traumatizing vector is effective anteriorly to this axis, then a flexion mechanism is the result (►Fig. 3). On the contrary, if the vector is effective posteriorly, then an extension injury will occur (see later). Thus the instantaneous axis of rotation has biomechanical implications on the deformity of the vertebral spine, regardless the level of an injury.7
Flexion and Compression, Burst, Extension, Fracture-Dislocation, and Luxation Injuries With moderate flexion and compression, a longitudinal pull is exerted on the anterior ligament complex. Because this is a very strong ligament, it usually remains intact, and, as a consequence, the anterior vertebral body has to bear most of the force, resulting in a wedge compression fracture. According to the Denis model,4 the anterior column is injured, without disruption of the posterior elements. These fractures are considered stable. The major radiologic feature is the diminished height of the anterior edge of a vertebral body. At the level of the cervical spine, the C5–C7 segments are mostly involved. However, in many cases, not only one segment is injured. Consequently, the entire spine should be thoroughly investigated in patients with a proven compression fracture (►Fig. 4). When a flexion mechanism is combined with a severe axial compression at the cervical spine, flexion teardrop fractures occur. In some classifications, these are described as a variant of burst fractures. They are typically caused by diving into shallow water or comparable accidents. The anteroinferior aspect of the vertebral body is fractured. This fragment is displaced anteriorly and resembles a teardrop. For this fragment to be produced, significant posterior ligamentous disruption must occur. The injury involves all three columns, rendering the injury highly unstable. This is often accompanied by spinal cord injury. A type I fracture is described as deterioration of the anterior vertebral edge, in Seminars in Musculoskeletal Radiology
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No. 3/2014
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Traumatized Vertebral Spine Revisited
Traumatized Vertebral Spine Revisited
Schueller, Schueller-Weidekamm
Fig. 3 (a) The instantaneous axis of rotation of the L1–L2 segment is marked in the anterocentral portion of L1 (dotted line). (b) If the traumatizing vector is effective anteriorly to this axis (arrow), a (c) flexion mechanism occurs (arrow).
combination with an anterior dislocation and a rupture of the anterior longitudinal ligament. A type II fracture is described as a teardrop fragment with discontinuity of the posterior vertebral edge and distended facet joints, as well as a widened interlaminar space. At the level of the thoracolumbar junction, this injury mechanism causes the Chance fracture.8 The vertebra is horizontally ruptured into two parts. In particular, the levels T10– L2 are involved. Anteriorly, only a discrete compression is seen. It is combined with a severe distraction of the posterior column. This fracture is unstable. In general, in high-speed injuries, the combination of an axial load and a flexion causes the upper body to bend forward while the lower body is fixed. Chance fractures are associated with mesenteric and bowel injury in about half of these cases. The Smith fracture is a variant of a horizontal flexion fracture. The disruption of the posterior spinal elements occurs through the interspinous ligaments while there is no difference in the remaining fracture patterns compared with the Chance fracture. A burst fracture occurs when a severe compressive force is transmitted to the spine axially and a disk fractures into its adjacent lower vertebral body, causing a disruption of this vertebral body (►Fig. 5). This injury mechanism leads to the disruption of the anterior and middle columns. The posterior column has variable degrees of injury. Radiologically, fragments are seen that narrow the spinal canal and compress the myelon. Burst fractures commonly involve the thoracic and the lumbar spine. At the upper cervical spine, a burst mechanism most often causes a Jefferson fracture.9 This is a synonym for a fracture of the atlas ring. The axial force is transmitted through the occipital condyles. It displaces the masses laterally and causes fractures of the anterior and posterior arches. The reason for the instability of the Jefferson fracture is the avulsion of the transverse ligament. Originally, a four-fragment fracture was described and is classified as a Gehweiler type III fracture.10 Seminars in Musculoskeletal Radiology
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However, three fragment fractures occur as well. In general, fractures of the atlas were classified by Gehweiler into five types. Type I and II fractures are isolated fractures of the anterior or posterior arches. These fractures are also referred to as nutcracker fractures because they are a result of an anterior distraction and posterior compression between the occipital condyles and the axis. Type IV and V fractures are isolated stable fractures of the lateral mass of the axis or of a transverse process, respectively. In particular, these fractures can lead to the dissection of the vertebral artery. Thus, in many trauma centers, cervical injuries are an indication for computed tomography (CT) angiography of the supraaortic branches. However, this technique is not based on evidence.11,12 If the traumatizing vector is effective dorsally in relation to the instantaneous axis of rotation, an extension mechanism occurs and leads to the distraction (i.e., elongation of the anterior column), according to the Denis model.4 Hyperextension lesions are rare. They are defined by an osseous and/or ligamentous disruption of all columns, and they are highly unstable. Radiologically, at the anterior column, a bony disruption is most often visible. More importantly, indirect signs of this injury are a retrolisthesis, as well as a widening of the intervertebral space and the interspinous distance. These findings occur due to severe soft tissue damage to the intervertebral disks and to the posterior vertebral elements. They are suitably diagnosed by magnetic resonance imaging (MRI). During motor vehicle accidents in particular, the injury mechanism includes the likelihood that the driver’s thorax, without the seat belt fastened, is pushed toward the steering wheel, and the face is slammed down on the windshield. At the level of the upper cervical spine, this injury mechanism causes traumatic spondylolysis of the axis, the Hangman fracture.13 The fracture involves the interarticulare parts bilaterally and/or the pedicles, the body, and the facets as well as the transverse processes. Also, the intervertebral disk C2–C3 is ruptured. The fractured pedicles, however, allow
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Fig. 5 Burst fracture of L1 with minor involvement of the posterior vertebral edge (arrow).
Fracture-dislocation, which is among the types of injury of the Denis classification,4 is caused by severe shear and rotational forces. Most often, these are combined with a substantial compression (e.g., these fractures are seen after a severe impact onto the patient́ s back while the lower body is rotated to one side). This occurs when passengers are ejected from a car or in comparable accidents. This injury includes vertebral disruption and comminution. It is associated with substantial neurologic symptoms. Fracture-dislocation injuries are associated with unilateral or bilateral facet joint luxations. A unilateral luxation is caused by the combination of rotation and flexion, whereas a bilateral luxation frequently occurs after rotation and compression.15 The bilateral luxation represents a highly unstable condition. The vertebral body dislocation in the injured segment is at least 50%.The articular malalignment is best visible on axial and sagittal images. It is referred to as the “naked” facet sign.16 Another radiologically useful sign is the “reversed hamburger bun” sign.17 It reflects a convex rather than a normal concave appearance of the articular surface. Most often, the thoracolumbar junction is involved because the physiologic biomechanical reduction of its vertebral joints makes them prone to a rotational injury.
Fig. 4 Multiple fractures (arrows) in a 53-year-old man after a fall from a height. Note the involvement of posterior vertebral elements in T9 and T10 (arrowheads) and of the middle column in L1 (asterisks).
decompression of the spinal canal. Thus neurologic symptoms do not appear as early because there is a combination of bilaterally blocked facet joints. A rotational component may cause an asymmetry of the fracture.14
Diagnostic Algorithm In the evaluation of patients with suspected vertebral spine trauma, several questions remain controversial: which patients need imaging, how much imaging is necessary, and what kind of imaging should be performed? Concerns about cost and radiation exposure require careful patient selection. Regarding cervical spine imaging, the most significant studies are the National Emergency Seminars in Musculoskeletal Radiology
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Traumatized Vertebral Spine Revisited
Traumatized Vertebral Spine Revisited
Schueller, Schueller-Weidekamm
X-radiography Utilization Study (NEXUS)18 and the Canadian Cervical Spine Prediction Rule Study (CCSPR).19 Both studies, together comprising > 43,000 patients, revealed comparable high sensitivities for identifying patients at risk for significant spine injury. This means that patients who meet the dedicated low-risk criteria that have been established by these studies (i.e., no midline cervical tenderness, no focal neurologic deficits, no intoxication or indication of brain injury, no painful distracting injuries, normal alertness) do not need imaging.18,19 However, adults who do not fulfill these low-risk criteria do require imaging. In a meta-analysis of seven studies, the pooled sensitivity of radiography for detecting patients with cervical spine injury was as low as 52%; the combined sensitivity of CT was 98%.20 Thus CT, and not radiography, should be the primary screening study for suspected cervical spine injury. Radiographic studies should be performed only when CT is not readily available and should not be considered a substitute for CT. The literature does not define a minimum section thickness, maximum voxel dimensions, or other technical factors for these images. However, we recommend a collimation of at least 1.5 mm. Three plane reformations should be performed. Flexion and extension views are not considered cost effective in cervical spine imaging in the trauma setting.21 However, flexion and extension imaging of the cervical spine could be useful in evaluating potential ligamentous injury in patients after normal or inconclusive MRI findings. It is generally accepted that soft tissue injuries are quite common after a significant spine trauma, and many of these lesions do not lead to mechanical instability. Unfortunately, MRI is not an unequivocal troubleshooter because, on the one hand, it potentially misses significant lesions, and, on the other, it also detects many clinically insignificant lesions. To date, there is not sufficient evidence to establish the reliability of the NEXUS criteria in younger children or to recommend whether radiography or CT should be the initial imaging study. In their study, Oman and coworkers enrolled 1,666 children with suspected spinal injury.22 The authors retrospectively applied the NEXUS criteria and found them to be reliable in children. The recommended protocol for cervical spine clearance included radiography as the first-line imaging study; CT and MRI are reserved for patients with inconclusive findings. Radiography is supposed to be of sufficiently high accuracy in imaging the pediatric population. One of the reasons may be that children experience cervical spine injury in a slightly different manner than adults. Children most often have injuries at the atlantooccipital and atlantodental segments, respectively. These are the regions where pediatric radiographs perform best. Thoracolumbar spine imaging is indicated if any of the following are present: high-energy trauma; back pain, or midline tenderness; local signs of thoracolumbar injury; abnormal neurologic signs; cervical spine fracture; Glasgow Coma Scale < 15; major distracting injury according to the referring physician; and alcohol or drug intoxication.23 The literature indicates no clear recommendation about which imaging modality should be used. However, these indications Seminars in Musculoskeletal Radiology
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Fig. 6 Non-recent type I lesion according to Bondurant et al 28: intramedullar bleeding shows a hypointense rim due to blood products nine months after trauma. Distal atrophy of the spinal cord is a result of the Wallerian degeneration in a chronic injury (arrow).
may also be considered as indications for CT imaging of the thorax and the abdomen. Imaging patients with neurologic symptoms is a matter for MRI. According to the criteria established by the American College of Roentgenology, MRI should be performed in patients whose neurologic status cannot be fully evaluated within 48 hours of injury including those in whom CT is normal.24 There is no clear evidence that MRI performed > 48 hours after an injury is of lower sensitivity than an acute MRI. Instead, the recommendation to perform MRI within 48 hours is due to concerns about keeping patients in collars unnecessarily for a prolonged period of time. Due to its high elasticity, the myelon of children is prone to severe trauma. However, symptoms in children often occur without correlation with MRI images: spinal cord injury without radiographic abnormality.25 Another challenge of spinal cord injuries is among the elderly, at least in part because of a preexisting narrowing of the spinal canal.26 The American Spinal Injury Association score is considered the reference in neurologic spine imaging, describing lesions from A (no function below the level of the injury) to E (normal function).27 From a radiologic point of view, medullary lesions are suitably discriminated after Bondurant et al.28 Findings are graded into three types, according to the presence of edema and cord swelling, blood products, or both (►Fig. 6). Therefore, these radiologic findings can be considered prognostic markers, which have been described previously.24
Conclusion Key variables, such as the delineation of instability, have implications for patients’ treatment and outcome, and they
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12 Malhotra AK, Camacho M, Ivatury RR, et al. Computed tomograph-
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Conflict of Interest The authors have nothing to disclose. 19
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Seminars in Musculoskeletal Radiology
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should not be discussed from a radiologic point of view only. Rather, the collaboration of radiologists with all other members of the trauma team is crucially important. A reasonable classification of vertebral spine trauma comprises criteria that include the injury mechanism as well as morphological and clinical findings. Such a classification represents a unique language between radiologists and clinicians. However, the ideal classification of spine trauma does not yet exist. Instead, we face many synonyms and eponyms (e.g., Jefferson fracture, Hangman fracture). They provide a high degree of specific information and should be fully understood by trauma radiologists because they contribute to interdisciplinary collaboration and communication. By relying on these few essentials, radiologists will serve as effective partners in the management of patients with vertebral spinal trauma.
Schueller, Schueller-Weidekamm
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