- Email: [email protected]
Multidetector Computed Tomography of Spinal Trauma: A Pictorial Review
Multidetector Computed Tomography of Spinal Trauma: A Pictorial Review K. Srinivasan, MBBS, Ankur Gadodia, MD, DNB, Atin Kumar, MD, DNB, and Shivanand Gamangatti, MD
Spinal trauma is 1 of the major causes of disability that commonly affects young adults, and radiologists play a crucial role in the evaluation of acutely traumatized patients. With the advent of multidetector computed tomography (MDCT), the algorithm of imaging of spinal trauma has changed dramatically and MDCT is now established as the imaging modality of choice for the diagnosis of spinal trauma. The appearance on MDCT of the spinal injury depends on the mechanism of the injury, which also determines the stability of the injury. This pictorial essay describes the MDCT appearances, mechanism, and stability of commonly encountered traumatic spinal injuries.
suspected spine injury.2 MDCT allows examination of the whole spine in a very short time and the ability to acquire volume data has also paved the way for the development of 3-dimensional image-processing techniques, such as multiplanar reformation (MPR) and volume-rendering techniques (VRT). The MPR images and the 3-dimensional images help in understanding the spatial relations, which is important for fracture classification and preoperative planning.3-5 The purpose of this pictorial review is to demonstrate the MDCT findings in spinal trauma.
Introduction
Role of MDCT
Spinal trauma is one of the major causes of disability that commonly affects young adults.1 The incidence of spinal injuries in the USA is between 4 and 5.3 per 100,000 population.2 There may be some degree of neurologic defect in about 10%-25% of patients with spinal trauma. The radiologist plays a crucial role in the evaluation of acutely traumatized patients by diagnosing the spinal injuries quickly and assisting the surgeons to intervene immediately. After the advent of multidetector computed tomography (MDCT), the role of conventional radiographs as an initial imaging modality for spinal trauma has decreased. The American College of Radiology (ACR) appropriateness criteria for imaging of the spinal trauma recommends thin-section computed tomography (CT) as a primary screening modality for From the Department of Radiology, JPNA Trauma Center, All India Institute of Medical Sciences, New Delhi, India. Reprint requests: Atin Kumar, MD, DNB, Assistant Professor, Department of Radiology, All India Institute of Medical Sciences, 175 Minakshi Garden Tilak Nagar, New Delhi, India 110018. E-mail: [email protected]. Curr Probl Diagn Radiol 2011;40:181-190. © 2011 Mosby, Inc. All rights reserved. 0363-0188/$36.00 ⫹ 0 doi:10.1067/j.cpradiol.2010.06.002
Curr Probl Diagn Radiol, September/October 2011
The role of imaging in spinal trauma is to diagnose the spinal injuries and to assess the stability of the injuries.6 Classification of Spinal Injuries Spinal injuries are classified according to the mechanism of injury—flexion, extension, or vertical compression.7,8 The commonly used functional classification is listed in Table 1. Stability of the Injuries The stability of spinal fractures is assessed by the 3-column concept proposed by Denis.6 According to this concept, the spine is divided into 3 columns. The anterior column comprises the anterior longitudinal ligament, the anterior annulus, and the anterior two thirds of the vertebral body. The middle column comprises the posterior longitudinal ligament, the posterior annulus, and the posterior one third of the vertebral body. The posterior column comprises pedicles, lamina, spinous processes, facets, and ligaments, including interspinous and supraspinous ligament and ligamentum flavum. The injury is considered unstable when more than 1 column is involved.
181
TABLE 1. Classification of spinal injuries Craniocervical junction: ● Occipital condyle fractures ● Atlanto occipital dislocation ● Fractures of atlas Jefferson fracture Lateral mass fracture Isolated fracture of C1 ● Atlanto-axial dislocation/subluxation ● Fractures of C 2 X Hangman fracture. X Odontoid fractures X Lateral mass fracture Lower cervical spine injuries: ● Flexion injuries X Clay shoveler fracture X Anterior subluxation X Simple wedge compression X Bilateral facet dislocation X Unilateral facet dislocation X Flexion teardrop fracture ● Extension injuries X Hyperextension injuries X Extension teardrop fractures X Laminar fractures X Pedico-laminar fracture ● Vertical compression injuries Thoracolumbar injuries ● Vertical compression injuries ● Flexion injuries X Wedge compression fracture X Chance fracture X Shear injury ● Lateral compression injury ● Extension injuries Transverse process fractures
TABLE 2. Classification of occipital condyle fractures Type
Mechanism
Type I
Axial compression
Type II
Direct skull trauma
Type III
Forced rotation and lateral bending
Imaging findings Comminuted fracture of the condyles Extension of basilar skull fracture (Fig 1) Avulsion fracture of the medial aspect of occipital condyle by the alar ligament (Fig 2)
Stability Stable Stable Unstable
FIG 1. Type II occipital condyle fracture in a 26-year-old male. Axial MDCT image shows the occipital bone fracture extending in to the right occipital condyle (arrow).
Injuries of Craniocervical Junction Occipital Condyle Fractures Occipital condyle fractures are rare and are often associated with craniocervical instability. The Anderson and Montesano classification,9 which is widely used for classifying the occipital condyle fractures (Table 2), is based on the mechanism of injury and fracture morphology (Figs 1 and 2)
Atlanto-Occipital Dislocation Atlanto-occipital dislocation is caused by severe flexion or extension resulting in the complete disruption of all ligamentous relationships between the occiput and atlas, which are provided by cruciate ligament, tectorial membrane, apical ligament, and alar ligaments. They are usually fatal, causing brain stem compression and, therefore, rarely present as a clinical problem. The commonly used method to diag-
182
nose this injury is the Harris rule of 12 or BAI-BDI method. By this rule, the basion-dental interval and basion-axial interval (distance between the basion and a line drawn along the posterior margin of the axis, which is extended superiorly) should not exceed 12 mm.
Fractures of the Atlas A Jefferson fracture is caused by vertical compression/axial loading forces transmitted through the occipital condyles to the lateral masses of atlas, resulting in bilateral fractures of the anterior and posterior arches of atlas.10,11 The lateral masses of C1 vertebra are displaced laterally with respect to the articular pillars of C2, which may be associated with disruption of the transverse ligament of the atlas, making it unstable. MDCT identifies the exact site of fracture and assesses displacement and spinal stability. The axial images show the sites and number of fractures
Curr Probl Diagn Radiol, September/October 2011
FIG 2. Occipital condyle fracture type III in a 25-year-old male. Coronal reformatted MDCT image demonstrates nondisplaced left occipital condyle fracture (arrow).
FIG 4. Isolated anterior arch fracture in a 36-year-old male. Axial MDCT image shows an isolated anterior arch fracture with no displacement of the fracture fragments.
growth of the atlas compared with C2, the lateral masses of C1 appear to be displaced laterally over C2, producing a pseudo Jefferson fracture.
Lateral Mass (C1) Fracture Isolated fractures of the lateral masses of C1 are usually caused by eccentric loading. They may be associated with occipital condyle fractures or fractures of the axis and are considered unstable as the transverse ligament is commonly disrupted.8
Isolated Fractures of Arch of C1
FIG 3. Jefferson fracture in a 20-year-old female. Axial CT image shows a single anterior arch fracture and 2 posterior arch fractures.
(Fig 3). Coronal reconstructions demonstrate the offset of the lateral articular masses of C1 in relation to the articular surfaces of C2.12 When the displacement is more than 6.9 mm, it indicates a transverse atlantal ligament rupture and the injury is unstable. Sagittal reconstructions are used to assess the atlanto-dental interval and a distance ⬎3 mm in adults implies transverse ligament rupture, making it unstable. The conditions that may simulate a Jefferson fracture include clefts and aplasias in the atlas ring. In children younger than 5 years, due to the increased
Curr Probl Diagn Radiol, September/October 2011
Isolated anterior and posterior arch fractures are usually stable. The anterior arch fractures are avulsion fractures of the anterior portion of the ring caused by avulsion by anterior longitudinal ligament and longus colli during hyperextension. The posterior arch fracture occurs when the neural arch of C1 is compressed between the occiput and the neural arch of C2 during hyperextension of the head on the neck (Fig 4). These fractures are better demonstrated on sagittal reconstructions.
Atlanto-Axial Subluxation Rotatory atlanto-axial subluxation is a frequently underdiagnosed condition. This is rare in adults and more common in children; the normal rotation of the atlas on the axis becomes limited or fixed. The mechanism of this injury is flexion along with rotation of C1. Axial images show the rotated position of the
183
FIG 5. Acute traumatic rupture of the transverse atlantal ligament in a 15-year-old male. (A) Axial image shows anterior displacement of atlas with widening of anterior atlanto dental interval. (B) Volume-rendered image shows widening of predental space. (Color version of figure is available online.)
atlas on the axis (Fig 5). In the coronal reconstructed images, the combined spread of the lateral masses of C1 on C2 vertebra will be ⬎7 mm when associated with rupture of the transverse ligament.8 Traumatic anterior atlanto-axial subluxation is caused by the rupture of the transverse ligament of the atlas, which normally restricts the forward movement of the atlas on axis. It is identified by an increase in the predentate (atlanto-dental) space of greater than 3 mm in adults and 5 mm in children in the sagittal images.
Fractures of Axis Hangman Fracture: Traumatic Spondylolisthesis of C2 A hangman fracture consists of bilateral fractures of the pars interarticularis of C2 vertebra with anterior displacement of C2 over C3 (Fig 6). These fractures are classified into 3 types (Effendi’s classification, Table 3) based on the degree of involvement of pars interarticularis, C2-3 disk, and articular facet.13 Type I is considered stable, whereas types II and III are considered unstable.
Odontoid Fractures Odontoid fractures are primarily caused by hyperflexion injuries, which produce anterior displacement of the dens, and also by hyperextension injuries, which produce posterior displacement of the dens. The Anderson and D’Alonso classification14 is based on the location of
184
FIG 6. Hangman’s fracture in a 41-year-old male. (A) Axial MDCT image shows bilateral hairline fractures of the pars interarticularis (arrows). (B) Sagittal reconstructed image shows fracture through the pars interarticularis with no displacement of the fracture fragments (arrow).
fracture site with respect to the dens and spinal stability (Table 4). Type II is the most common type of odontoid fracture, which is seen as a transverse fracture through the base of the odontoid. This lesion is unstable and associated with a high incidence of nonunion due to reduced vascular supply. Os-odontoideum (Fig 9), a developmental anomaly, can be differentiated from the type II fracture by its round and sclerotic margins with a wide zone of separation from the body of axis and enlarged anterior tubercle of the atlas. Coronal and sagittal reconstructions are particularly useful in demonstration of type 2 fracture, which can be missed on axial planes.
Curr Probl Diagn Radiol, September/October 2011
TABLE 3. Classification of hangman fracture Type
Mechanism
Imaging findings
Stability
Type I
Axial loading with hyperextension
Stable
Type II
Hyperextension with axial loading followed by flexion
Type III
Primary flexion followed by rebound hyperextension
Hairline fracture through pars interarticularis with minimal displacement Bilateral fractures through pars interarticularis with C2-3 disk disruption Type II ⫹ articular facet dislocation
Unstable
Unstable
TABLE 4. Classification of odontoid fractures Type Type I
Type II FIG 7. Type 1 odontoid fracture in a 24-year-old male. Sagittal reconstructed MDCT image shows an oblique fracture through the dens above the junction of the dens with the body of the axis.
Type III
Imaging features Oblique fracture of the tip of dens due to the avulsion of alar ligament (Fig 7) Transverse fracture through the base of the odontoid (Fig 8) Fracture through the base of the odontoid and extending into the body of axis (Fig 10)
Stability Stable
Unstable
Stable
posterior ligament’s disruption. Usually there will be no bony injury. The anterior longitudinal ligament is intact. This injury is mechanically and neurologically stable. Sagittal reconstructions show a hyperkyphotic angulation at the level of injury, anterior displacement of the vertebra, widening of the interspinous space (“fanning”), anterior narrowing and posterior widening of the disk space, lack of parallelism of the facets, and partial uncovering of the facets of the subluxated apophyseal joints.8 Bilateral Facet Dislocation FIG 8. Type II odontoid fracture in 30-year-old male. Coronal reconstructed MDCT image shows a transverse fracture through the base of the odontoid (arrow).
Lower Cervical Spine Injuries: Flexion Injuries Anterior Subluxation (Hyper Flexion Sprain) Anterior subluxation occurs when there is an incomplete anterior dislocation of the facet joints due to the
Curr Probl Diagn Radiol, September/October 2011
Bilateral facet dislocation is caused by a combination of the extreme degrees of anterior subluxation and flexion, causing disruption of the annulus fibrosus, anterior longitudinal ligament, and posterior ligamentous complex. It usually occurs in the lower cervical spine and is an extremely unstable condition. On the axial images, the facet dislocation is seen as the reverse in orientation of the superior and inferior facets, which is referred to as a reverse hamburger bun sign (Fig 11). Sagittal images show ⬎50% displacement of the anteroposterior diameter of the vertebral body.
185
FIG 9. Os odontoideum in a 14-year-old male. Sagittal reconstructed image shows a rounded ossicle (arrow) with sclerotic margins and widely separated from the body of axis and enlarged tubercle of atlas.
FIG 10. Type III odontoid fracture in a 54-year-old male. Sagittal reconstructed MDCT image shows an oblique fracture extending in to the body of axis (arrow).
Simple Wedge Compression Fracture Due to the dislocation, the tip of the articular facets of adjacent vertebrae levels lies in apposition and are referred to as a perched facet sign.15 The fracture of superior and inferior facets, if present, can also be seen. VRT clearly demonstrates the dislocation and the associated fractures of the articular pillars (Fig 12).
Anterior wedging of the superior vertebral endplate occurs with hyperflexion and compression injuries.16 In the sagittal images, there is reduced anterior height (with not ⬎25% compression of the anterior column) of the vertebral body. The middle column is usually preserved, making this injury stable.
Unilateral Facet Dislocation
Clay Shoveler Fracture
The combination of flexion and distraction forces causes the inferior facet of the upper vertebra to dislocate anterior to the superior facet of the subjacent vertebra fixing in the intervertebral foramen (locked vertebra). Sagittal reconstructed images show anterior translation of the vertebra at about 25%-50% of the anteroposterior diameter of the vertebral body, which is less than that of bilateral dislocation. The interspinous distance is widened at the level of injury as the posterior ligaments are torn on the side of the dislocation. There may be kyphotic angulation at the level of injury, implying the flexion mechanism. The axial images may show reversed orientation of the facets (reverse hamburger bun sign). Additional fractures in the vertebral body can be also be detected in the axial images. Because of the locking mechanism, the pure unilateral facet dislocation is stable.
Clay shoveler’s fracture is an avulsion injury of the base of the spinous process of the lower cervical spine caused by abrupt hyperflexion with lower neck muscular contraction or a direct blow to the neck (Fig 13). It is considered mechanically stable as the posterior ligament complex is unaffected.8
186
Flexion Tear Drop Fracture Flexion teardrop fracture is caused by the sudden hyperflexion with axial compression, resulting in a comminuted fracture of the vertebral body with a displaced teardrop fragment anteriorly and disruption of all 3 columns—anterior and posterior longitudinal ligament and posterior ligamentous complex. Sagittal images demonstrate fracture fragment, hyperkyphotic angulation at the level of injury, widening of the interspinous distance, and displacement of vertebral
Curr Probl Diagn Radiol, September/October 2011
FIG 11. Bilateral facet dislocation. (A) Axial image showing the normal orientation of the facets, ie, the flattened surfaces of the facets face each other resembling a hamburger bun. (B) Axial image showing the reverse hamburger bun sign, ie, the rounded surfaces of the facets face other.
FIG 12. Bilateral facet dislocation in a 32-year-old male. (A) Sagittal reconstructed image shows the anterolisthesis of the facet of C6 over C7. (B) Volume-rendering image shows ⬎50% anterior displacement of C6 over C7 (arrow). (Color version of figure is available online.)
body into the spinal canal (Fig 14). This injury is unstable and is associated with a high incidence of cord injury. Hyperextension Injuries Hyperextension injuries of the cervical spine are characterized by distraction of the anterior and middle columns and by compression of the posterior column
Curr Probl Diagn Radiol, September/October 2011
FIG 13. Clay shoveler fracture in a 26-year-old male. Sagittal reconstructed MDCT image shows oblique fractures in the spinous process of C6 and C7.
with avulsion injuries anteriorly and impaction injuries posteriorly. Hyperextension dislocation is primarily a soft tissue injury due to momentary posterior dislocation of the involved cervical vertebrae. It results in tearing of the longus colli and longus capitis muscles, disruption of the anterior longitudinal ligament, posterior longitudinal ligament, and the ligamentum flavum with horizontal disruption of the annulus and disk. Sagittal
187
FIG 15. Laminar fracture in a 36-year-old female. Axial CT image shows comminuted fracture of the left lamina without any displacement of fracture fragment into the spinal canal.
Laminar Fractures FIG 14. Flexion teardrop fracture in a 22-year-old male. Sagittal reconstructed MDCT image shows a small fracture fragment from the anteroinferior aspect of the C6 with kyphotic angulation at the level of injury.
images show prevertebral soft tissue swelling and a triangular fragment in the anteroinferior aspect of body of the superior vertebra. The alignment of the vertebrae may be normal due to the realignment after the removal of the force. The disk spaces are widened anteriorly. The transverse diameter of the avulsed fragment is more than its vertical height and can be differentiated from an extension teardrop in which the transverse diameter is equal to or less than its vertical height. In a hyperextension fracture dislocation, there will be compression fractures of the pedicles, lamina, articular pillars, and the spinous processes in addition to the soft tissue injuries described above.
Laminar fractures usually occur due to hyperextension injuries and they may be associated with burst fractures or flexion teardrop fractures. Axial images show simple or comminuted fractures of one or both lamina (Fig 15). Isolated laminar fractures are usually stable. The fragments, when displaced into the spinal canal, should be identified as they are unstable. Pedicolaminar Fracture/Separation A pedicolaminar fracture/separation is caused by either hyperextension in rotation or hyperflexion in flexion due to a combination of ligamentous and osseous injuries. MDCT shows a simultaneous fracture of ipsilateral pedicle and lamina, resulting in a separation of the articular pillar. The parasagittal reconstructed images show anterior rotation of the articular pillar.
Extension Teardrop Fractures
Thoracolumbar Injuries
Extension teardrop fractures are an avulsion injury occurring due to the rupture of the anterior longitudinal ligament during sudden hyperextension.17 They may be associated with prevertebral hematoma. The transverse diameter of the teardrop is less than the vertical height. The disk spaces may show anterior widening. They are both neurologically and mechanically stable.
Vertical Compression Injuries
188
Axial loading causes the compression forces to be transmitted to the intervertebral disk space, resulting in propulsion of the nucleus pulposus into vertebral body through the endplate. This results in a burst fracture in which the fragments are displaced centrifugally. They are more common at the thoracolumbar
Curr Probl Diagn Radiol, September/October 2011
FIG 16. Vertical compression fracture in a 56-year-old male. (A) Sagittal reconstructed MDCT image shows the burst fracture of D12 vertebra with mild posterior displacement of the fracture fragment in to the spinal canal. (B) VRT clearly demonstrates the burst fracture of D-12 vertebra. (C) Coronal reconstructed MDCT image shows associated laminar split fracture in the same patient. (Color version of figure is available online.)
junction.17,18 Sagittal images demonstrate reduced anterior and posterior height of the vertebral body with posterior displacement of the posterior fragment into the spinal canal (Fig 16). Axial images show a comminuted fracture in the involved vertebra and associated laminar fracture if present. Signs of instability include widening of the interspinous and interlaminar distance, translation of more than 2 mm, kyphosis of more than 20 degrees, dislocation, height loss of more than 50%, and articular process fractures.8
Flexion Compression Injuries Flexion compression injuries are the most common thoracolumbar fractures. Sudden hyperflexion causes mechanical compression of the involved vertebra, resulting in anterior wedging of superior endplate.18 Posterior longitudinal ligament is intact in typical wedging. The typical anterior wedge fracture is stable as the middle column is preserved. Sagittal images show reduced anterior height of the vertebral body with preserved posterior vertebral body (Fig 17). Widening of the interspinous distance and focal kyphotic deformity indicates associated posterior ligamentous injury.
Curr Probl Diagn Radiol, September/October 2011
FIG 17. Flexion-compression fracture in a 39-year-old male. (A) Sagittal reconstructed image shows anterior wedging of L2 vertebra with relatively preserved posterior height. (B) Coronal reconstructed MDCT image shows typical wedging of L2 vertebra.
Shear Injury Shear injury is characterized by disruption of all 3 columns with anterior, posterior, or lateral displacement of the vertebra, depending on the direction of the force. The most frequent type is the anterior displacement of the vertebra with associated spinal cord injury. This is highly unstable and may be associated with visceral injuries.
Flexion—Distraction Injuries (Chance Fracture) This injury is caused by hyperflexion of the spine with distraction of the posterior elements (Fig 18). Chance fracture is common in automobile accidents when there is acute forward flexion of the spine across a restraining lap seatbelt during sudden deceleration (lap-belt fracture). The classic chance fracture is a horizontal fracture through the spinous process, laminae, pedicles, and vertebral body without any ligament injury. The chance variants include pure soft tissue injuries or combined bony-soft tissue injuries that may show horizontal split in the intervertebral disks and ligaments.
Hyper Extension Injuries Hyperextension injuries are extremely rare injuries and occur when there is a direct blow to the back or when the upper trunk is thrust backwards. These injuries are common in patients with ankylosing spon-
189
is now regarded as the primary investigation tool of choice.
REFERENCES
FIG 18. Chance fracture in a 48-year-old male. (A) Sagittal reconstructed MDCT image shows a horizontal fracture extending through the spinous process, pedicle, and vertebral body. (B) Volume-rendered (VRT) image shows the horizontal fracture extending through the vertebral body (arrow). (Color version of figure is available online.)
dylitis. It is characterized by compression/impaction of the posterior elements manifested by fractures (often comminuted) of the spinous process, lamina, or facets. In addition, there may be distraction of the anterior column manifested by anterior disk widening or avulsion fracture from the anterosuperior vertebral body. In severe injuries, there may be complete loss of continuity of upper and lower spinal segment resulting in paraplegia (lumberjack fracture-dislocation).
Transverse Process Fractures The mechanisms involved in these fractures include avulsion of the psoas muscle, lateral flexion-extension forces, or direct blunt trauma. These injuries may act as an indirect sign of associated abdominal visceral injuries or another spine fracture at a different level.
Conclusions Injuries to the spine result in significant mortality and morbidity. MDCT, with MPR and VRT reformations, is highly valuable for diagnosis, surgical planning, and management of spinal trauma. MDCT displays the complex anatomy of spine accurately and rapidly and thus accelerates the diagnostic process in spinal trauma victims. MDCT is the most sensitive method for imaging of osseous injuries in trauma patients and
190
1. Gonzalez-Beicos A, Nunez DB Jr. Role of multidetector computed tomography in the assessment of cervical spine trauma. Semin Ultrasound CT MR 2009;30:159-67. 2. American College of Radiology. Expert Panel on Musculoskeletal Imaging. Appropriateness criteria for suspected cervical spine trauma. ACR appropriateness criteria Available from: http://www.guideline.gov/summary/summary.aspx?doc_ id_8587. Reston, VA, 2002. 3. Geijer M, El-Khoury GY. MDCT in the evaluation of skeletal trauma: principles, protocols, and clinical applications. Emerg Radiol 2006;13:7-18. 4. Blackmore CC, Mann FA, Wilson AJ. Helical CT in the primary trauma evaluation of the cervical spine: an evidencebased approach. Skeletal Radiol 2000;29:632-9. 5. Li AE, Fishman EK. Cervical spine trauma: evaluation by multidetector CT and three-dimensional volume rendering. Emerg Radiol 2003;10:34-9. 6. Denis F. Three-column spine and its significance in classification of acute thoracolumbar spine injuries. Spine 1983;8: 817-32. 7. Bagley LJ. Imaging of spinal trauma. Radiol Clin North Am 2006;44:1-12. 8. Greenspan A. Spine. In: Greenspan A, editor. Orthopedic Radiology—A Practical Approach, 4th ed. New York: Lipincott Williams Wilkins, 2004. p. 349-410. 9. Anderson PA, Montesano PX. Morphology and treatment of occipital condyle fractures. Spine 1988;13:731-6. 10. Sherk HH. Fractures of the atlas and odontoid process. Orthop Clin North Am 1978;9:973-83. 11. Hays MB, Alker GJ Jr. Fractures of the atlas vertebra. The two-part burst fracture of Jefferson. Spine 1988;13:601-3. 12. Kesterson L, Benzel E, Orrison W, Coleman J. Evaluation and treatment of atlas burst fractures (Jefferson fractures). J Neurosurg 1991;75:213-20. 13. Effendi B, Roy D, Cornish B, et al. Fractures of the ring of the axis. A classification based on the analysis of 131 cases. J Bone Joint Surg 1981;63:319-27. 14. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg 1974;56:1663-74. 15. Ebraheim NA, Xu R, Ahmad M, et al. The effect of anterior translation of the vertebra on the canal size in the lower cervical spine: a computer-assisted anatomic study. J Spinal Disord 1997;10:162-6. 16. Campbell SE, Phillips CD, Dubovsky E, et al. The value of CT in determining potential instability of simple wedge-compression fractures of the lumbar spine. AJNR Am J Neuroradiol 1995;16:1385-92. 17. Stabler A, Eck J, Penning R, et al. Cervical spine: postmortem assessment of accident injuries—Comparison of radiographic, MR imaging, anatomic, and pathologic findings. Radiology 2001;221:340-6. 18. Dai LY. Imaging diagnosis of thoracolumbar burst fractures. Chin Med Sci J 2004;19:142-4.
Curr Probl Diagn Radiol, September/October 2011
Spinal trauma is 1 of the major causes of disability that commonly affects young adults, and radiologists play a crucial role in the evaluation of acutely traumatized patients. With the advent of multidetector computed tomography (MDCT), the algorithm of imaging of spinal trauma has changed dramatically and MDCT is now established as the imaging modality of choice for the diagnosis of spinal trauma. The appearance on MDCT of the spinal injury depends on the mechanism of the injury, which also determines the stability of the injury. This pictorial essay describes the MDCT appearances, mechanism, and stability of commonly encountered traumatic spinal injuries.
suspected spine injury.2 MDCT allows examination of the whole spine in a very short time and the ability to acquire volume data has also paved the way for the development of 3-dimensional image-processing techniques, such as multiplanar reformation (MPR) and volume-rendering techniques (VRT). The MPR images and the 3-dimensional images help in understanding the spatial relations, which is important for fracture classification and preoperative planning.3-5 The purpose of this pictorial review is to demonstrate the MDCT findings in spinal trauma.
Introduction
Role of MDCT
Spinal trauma is one of the major causes of disability that commonly affects young adults.1 The incidence of spinal injuries in the USA is between 4 and 5.3 per 100,000 population.2 There may be some degree of neurologic defect in about 10%-25% of patients with spinal trauma. The radiologist plays a crucial role in the evaluation of acutely traumatized patients by diagnosing the spinal injuries quickly and assisting the surgeons to intervene immediately. After the advent of multidetector computed tomography (MDCT), the role of conventional radiographs as an initial imaging modality for spinal trauma has decreased. The American College of Radiology (ACR) appropriateness criteria for imaging of the spinal trauma recommends thin-section computed tomography (CT) as a primary screening modality for From the Department of Radiology, JPNA Trauma Center, All India Institute of Medical Sciences, New Delhi, India. Reprint requests: Atin Kumar, MD, DNB, Assistant Professor, Department of Radiology, All India Institute of Medical Sciences, 175 Minakshi Garden Tilak Nagar, New Delhi, India 110018. E-mail: [email protected]. Curr Probl Diagn Radiol 2011;40:181-190. © 2011 Mosby, Inc. All rights reserved. 0363-0188/$36.00 ⫹ 0 doi:10.1067/j.cpradiol.2010.06.002
Curr Probl Diagn Radiol, September/October 2011
The role of imaging in spinal trauma is to diagnose the spinal injuries and to assess the stability of the injuries.6 Classification of Spinal Injuries Spinal injuries are classified according to the mechanism of injury—flexion, extension, or vertical compression.7,8 The commonly used functional classification is listed in Table 1. Stability of the Injuries The stability of spinal fractures is assessed by the 3-column concept proposed by Denis.6 According to this concept, the spine is divided into 3 columns. The anterior column comprises the anterior longitudinal ligament, the anterior annulus, and the anterior two thirds of the vertebral body. The middle column comprises the posterior longitudinal ligament, the posterior annulus, and the posterior one third of the vertebral body. The posterior column comprises pedicles, lamina, spinous processes, facets, and ligaments, including interspinous and supraspinous ligament and ligamentum flavum. The injury is considered unstable when more than 1 column is involved.
181
TABLE 1. Classification of spinal injuries Craniocervical junction: ● Occipital condyle fractures ● Atlanto occipital dislocation ● Fractures of atlas Jefferson fracture Lateral mass fracture Isolated fracture of C1 ● Atlanto-axial dislocation/subluxation ● Fractures of C 2 X Hangman fracture. X Odontoid fractures X Lateral mass fracture Lower cervical spine injuries: ● Flexion injuries X Clay shoveler fracture X Anterior subluxation X Simple wedge compression X Bilateral facet dislocation X Unilateral facet dislocation X Flexion teardrop fracture ● Extension injuries X Hyperextension injuries X Extension teardrop fractures X Laminar fractures X Pedico-laminar fracture ● Vertical compression injuries Thoracolumbar injuries ● Vertical compression injuries ● Flexion injuries X Wedge compression fracture X Chance fracture X Shear injury ● Lateral compression injury ● Extension injuries Transverse process fractures
TABLE 2. Classification of occipital condyle fractures Type
Mechanism
Type I
Axial compression
Type II
Direct skull trauma
Type III
Forced rotation and lateral bending
Imaging findings Comminuted fracture of the condyles Extension of basilar skull fracture (Fig 1) Avulsion fracture of the medial aspect of occipital condyle by the alar ligament (Fig 2)
Stability Stable Stable Unstable
FIG 1. Type II occipital condyle fracture in a 26-year-old male. Axial MDCT image shows the occipital bone fracture extending in to the right occipital condyle (arrow).
Injuries of Craniocervical Junction Occipital Condyle Fractures Occipital condyle fractures are rare and are often associated with craniocervical instability. The Anderson and Montesano classification,9 which is widely used for classifying the occipital condyle fractures (Table 2), is based on the mechanism of injury and fracture morphology (Figs 1 and 2)
Atlanto-Occipital Dislocation Atlanto-occipital dislocation is caused by severe flexion or extension resulting in the complete disruption of all ligamentous relationships between the occiput and atlas, which are provided by cruciate ligament, tectorial membrane, apical ligament, and alar ligaments. They are usually fatal, causing brain stem compression and, therefore, rarely present as a clinical problem. The commonly used method to diag-
182
nose this injury is the Harris rule of 12 or BAI-BDI method. By this rule, the basion-dental interval and basion-axial interval (distance between the basion and a line drawn along the posterior margin of the axis, which is extended superiorly) should not exceed 12 mm.
Fractures of the Atlas A Jefferson fracture is caused by vertical compression/axial loading forces transmitted through the occipital condyles to the lateral masses of atlas, resulting in bilateral fractures of the anterior and posterior arches of atlas.10,11 The lateral masses of C1 vertebra are displaced laterally with respect to the articular pillars of C2, which may be associated with disruption of the transverse ligament of the atlas, making it unstable. MDCT identifies the exact site of fracture and assesses displacement and spinal stability. The axial images show the sites and number of fractures
Curr Probl Diagn Radiol, September/October 2011
FIG 2. Occipital condyle fracture type III in a 25-year-old male. Coronal reformatted MDCT image demonstrates nondisplaced left occipital condyle fracture (arrow).
FIG 4. Isolated anterior arch fracture in a 36-year-old male. Axial MDCT image shows an isolated anterior arch fracture with no displacement of the fracture fragments.
growth of the atlas compared with C2, the lateral masses of C1 appear to be displaced laterally over C2, producing a pseudo Jefferson fracture.
Lateral Mass (C1) Fracture Isolated fractures of the lateral masses of C1 are usually caused by eccentric loading. They may be associated with occipital condyle fractures or fractures of the axis and are considered unstable as the transverse ligament is commonly disrupted.8
Isolated Fractures of Arch of C1
FIG 3. Jefferson fracture in a 20-year-old female. Axial CT image shows a single anterior arch fracture and 2 posterior arch fractures.
(Fig 3). Coronal reconstructions demonstrate the offset of the lateral articular masses of C1 in relation to the articular surfaces of C2.12 When the displacement is more than 6.9 mm, it indicates a transverse atlantal ligament rupture and the injury is unstable. Sagittal reconstructions are used to assess the atlanto-dental interval and a distance ⬎3 mm in adults implies transverse ligament rupture, making it unstable. The conditions that may simulate a Jefferson fracture include clefts and aplasias in the atlas ring. In children younger than 5 years, due to the increased
Curr Probl Diagn Radiol, September/October 2011
Isolated anterior and posterior arch fractures are usually stable. The anterior arch fractures are avulsion fractures of the anterior portion of the ring caused by avulsion by anterior longitudinal ligament and longus colli during hyperextension. The posterior arch fracture occurs when the neural arch of C1 is compressed between the occiput and the neural arch of C2 during hyperextension of the head on the neck (Fig 4). These fractures are better demonstrated on sagittal reconstructions.
Atlanto-Axial Subluxation Rotatory atlanto-axial subluxation is a frequently underdiagnosed condition. This is rare in adults and more common in children; the normal rotation of the atlas on the axis becomes limited or fixed. The mechanism of this injury is flexion along with rotation of C1. Axial images show the rotated position of the
183
FIG 5. Acute traumatic rupture of the transverse atlantal ligament in a 15-year-old male. (A) Axial image shows anterior displacement of atlas with widening of anterior atlanto dental interval. (B) Volume-rendered image shows widening of predental space. (Color version of figure is available online.)
atlas on the axis (Fig 5). In the coronal reconstructed images, the combined spread of the lateral masses of C1 on C2 vertebra will be ⬎7 mm when associated with rupture of the transverse ligament.8 Traumatic anterior atlanto-axial subluxation is caused by the rupture of the transverse ligament of the atlas, which normally restricts the forward movement of the atlas on axis. It is identified by an increase in the predentate (atlanto-dental) space of greater than 3 mm in adults and 5 mm in children in the sagittal images.
Fractures of Axis Hangman Fracture: Traumatic Spondylolisthesis of C2 A hangman fracture consists of bilateral fractures of the pars interarticularis of C2 vertebra with anterior displacement of C2 over C3 (Fig 6). These fractures are classified into 3 types (Effendi’s classification, Table 3) based on the degree of involvement of pars interarticularis, C2-3 disk, and articular facet.13 Type I is considered stable, whereas types II and III are considered unstable.
Odontoid Fractures Odontoid fractures are primarily caused by hyperflexion injuries, which produce anterior displacement of the dens, and also by hyperextension injuries, which produce posterior displacement of the dens. The Anderson and D’Alonso classification14 is based on the location of
184
FIG 6. Hangman’s fracture in a 41-year-old male. (A) Axial MDCT image shows bilateral hairline fractures of the pars interarticularis (arrows). (B) Sagittal reconstructed image shows fracture through the pars interarticularis with no displacement of the fracture fragments (arrow).
fracture site with respect to the dens and spinal stability (Table 4). Type II is the most common type of odontoid fracture, which is seen as a transverse fracture through the base of the odontoid. This lesion is unstable and associated with a high incidence of nonunion due to reduced vascular supply. Os-odontoideum (Fig 9), a developmental anomaly, can be differentiated from the type II fracture by its round and sclerotic margins with a wide zone of separation from the body of axis and enlarged anterior tubercle of the atlas. Coronal and sagittal reconstructions are particularly useful in demonstration of type 2 fracture, which can be missed on axial planes.
Curr Probl Diagn Radiol, September/October 2011
TABLE 3. Classification of hangman fracture Type
Mechanism
Imaging findings
Stability
Type I
Axial loading with hyperextension
Stable
Type II
Hyperextension with axial loading followed by flexion
Type III
Primary flexion followed by rebound hyperextension
Hairline fracture through pars interarticularis with minimal displacement Bilateral fractures through pars interarticularis with C2-3 disk disruption Type II ⫹ articular facet dislocation
Unstable
Unstable
TABLE 4. Classification of odontoid fractures Type Type I
Type II FIG 7. Type 1 odontoid fracture in a 24-year-old male. Sagittal reconstructed MDCT image shows an oblique fracture through the dens above the junction of the dens with the body of the axis.
Type III
Imaging features Oblique fracture of the tip of dens due to the avulsion of alar ligament (Fig 7) Transverse fracture through the base of the odontoid (Fig 8) Fracture through the base of the odontoid and extending into the body of axis (Fig 10)
Stability Stable
Unstable
Stable
posterior ligament’s disruption. Usually there will be no bony injury. The anterior longitudinal ligament is intact. This injury is mechanically and neurologically stable. Sagittal reconstructions show a hyperkyphotic angulation at the level of injury, anterior displacement of the vertebra, widening of the interspinous space (“fanning”), anterior narrowing and posterior widening of the disk space, lack of parallelism of the facets, and partial uncovering of the facets of the subluxated apophyseal joints.8 Bilateral Facet Dislocation FIG 8. Type II odontoid fracture in 30-year-old male. Coronal reconstructed MDCT image shows a transverse fracture through the base of the odontoid (arrow).
Lower Cervical Spine Injuries: Flexion Injuries Anterior Subluxation (Hyper Flexion Sprain) Anterior subluxation occurs when there is an incomplete anterior dislocation of the facet joints due to the
Curr Probl Diagn Radiol, September/October 2011
Bilateral facet dislocation is caused by a combination of the extreme degrees of anterior subluxation and flexion, causing disruption of the annulus fibrosus, anterior longitudinal ligament, and posterior ligamentous complex. It usually occurs in the lower cervical spine and is an extremely unstable condition. On the axial images, the facet dislocation is seen as the reverse in orientation of the superior and inferior facets, which is referred to as a reverse hamburger bun sign (Fig 11). Sagittal images show ⬎50% displacement of the anteroposterior diameter of the vertebral body.
185
FIG 9. Os odontoideum in a 14-year-old male. Sagittal reconstructed image shows a rounded ossicle (arrow) with sclerotic margins and widely separated from the body of axis and enlarged tubercle of atlas.
FIG 10. Type III odontoid fracture in a 54-year-old male. Sagittal reconstructed MDCT image shows an oblique fracture extending in to the body of axis (arrow).
Simple Wedge Compression Fracture Due to the dislocation, the tip of the articular facets of adjacent vertebrae levels lies in apposition and are referred to as a perched facet sign.15 The fracture of superior and inferior facets, if present, can also be seen. VRT clearly demonstrates the dislocation and the associated fractures of the articular pillars (Fig 12).
Anterior wedging of the superior vertebral endplate occurs with hyperflexion and compression injuries.16 In the sagittal images, there is reduced anterior height (with not ⬎25% compression of the anterior column) of the vertebral body. The middle column is usually preserved, making this injury stable.
Unilateral Facet Dislocation
Clay Shoveler Fracture
The combination of flexion and distraction forces causes the inferior facet of the upper vertebra to dislocate anterior to the superior facet of the subjacent vertebra fixing in the intervertebral foramen (locked vertebra). Sagittal reconstructed images show anterior translation of the vertebra at about 25%-50% of the anteroposterior diameter of the vertebral body, which is less than that of bilateral dislocation. The interspinous distance is widened at the level of injury as the posterior ligaments are torn on the side of the dislocation. There may be kyphotic angulation at the level of injury, implying the flexion mechanism. The axial images may show reversed orientation of the facets (reverse hamburger bun sign). Additional fractures in the vertebral body can be also be detected in the axial images. Because of the locking mechanism, the pure unilateral facet dislocation is stable.
Clay shoveler’s fracture is an avulsion injury of the base of the spinous process of the lower cervical spine caused by abrupt hyperflexion with lower neck muscular contraction or a direct blow to the neck (Fig 13). It is considered mechanically stable as the posterior ligament complex is unaffected.8
186
Flexion Tear Drop Fracture Flexion teardrop fracture is caused by the sudden hyperflexion with axial compression, resulting in a comminuted fracture of the vertebral body with a displaced teardrop fragment anteriorly and disruption of all 3 columns—anterior and posterior longitudinal ligament and posterior ligamentous complex. Sagittal images demonstrate fracture fragment, hyperkyphotic angulation at the level of injury, widening of the interspinous distance, and displacement of vertebral
Curr Probl Diagn Radiol, September/October 2011
FIG 11. Bilateral facet dislocation. (A) Axial image showing the normal orientation of the facets, ie, the flattened surfaces of the facets face each other resembling a hamburger bun. (B) Axial image showing the reverse hamburger bun sign, ie, the rounded surfaces of the facets face other.
FIG 12. Bilateral facet dislocation in a 32-year-old male. (A) Sagittal reconstructed image shows the anterolisthesis of the facet of C6 over C7. (B) Volume-rendering image shows ⬎50% anterior displacement of C6 over C7 (arrow). (Color version of figure is available online.)
body into the spinal canal (Fig 14). This injury is unstable and is associated with a high incidence of cord injury. Hyperextension Injuries Hyperextension injuries of the cervical spine are characterized by distraction of the anterior and middle columns and by compression of the posterior column
Curr Probl Diagn Radiol, September/October 2011
FIG 13. Clay shoveler fracture in a 26-year-old male. Sagittal reconstructed MDCT image shows oblique fractures in the spinous process of C6 and C7.
with avulsion injuries anteriorly and impaction injuries posteriorly. Hyperextension dislocation is primarily a soft tissue injury due to momentary posterior dislocation of the involved cervical vertebrae. It results in tearing of the longus colli and longus capitis muscles, disruption of the anterior longitudinal ligament, posterior longitudinal ligament, and the ligamentum flavum with horizontal disruption of the annulus and disk. Sagittal
187
FIG 15. Laminar fracture in a 36-year-old female. Axial CT image shows comminuted fracture of the left lamina without any displacement of fracture fragment into the spinal canal.
Laminar Fractures FIG 14. Flexion teardrop fracture in a 22-year-old male. Sagittal reconstructed MDCT image shows a small fracture fragment from the anteroinferior aspect of the C6 with kyphotic angulation at the level of injury.
images show prevertebral soft tissue swelling and a triangular fragment in the anteroinferior aspect of body of the superior vertebra. The alignment of the vertebrae may be normal due to the realignment after the removal of the force. The disk spaces are widened anteriorly. The transverse diameter of the avulsed fragment is more than its vertical height and can be differentiated from an extension teardrop in which the transverse diameter is equal to or less than its vertical height. In a hyperextension fracture dislocation, there will be compression fractures of the pedicles, lamina, articular pillars, and the spinous processes in addition to the soft tissue injuries described above.
Laminar fractures usually occur due to hyperextension injuries and they may be associated with burst fractures or flexion teardrop fractures. Axial images show simple or comminuted fractures of one or both lamina (Fig 15). Isolated laminar fractures are usually stable. The fragments, when displaced into the spinal canal, should be identified as they are unstable. Pedicolaminar Fracture/Separation A pedicolaminar fracture/separation is caused by either hyperextension in rotation or hyperflexion in flexion due to a combination of ligamentous and osseous injuries. MDCT shows a simultaneous fracture of ipsilateral pedicle and lamina, resulting in a separation of the articular pillar. The parasagittal reconstructed images show anterior rotation of the articular pillar.
Extension Teardrop Fractures
Thoracolumbar Injuries
Extension teardrop fractures are an avulsion injury occurring due to the rupture of the anterior longitudinal ligament during sudden hyperextension.17 They may be associated with prevertebral hematoma. The transverse diameter of the teardrop is less than the vertical height. The disk spaces may show anterior widening. They are both neurologically and mechanically stable.
Vertical Compression Injuries
188
Axial loading causes the compression forces to be transmitted to the intervertebral disk space, resulting in propulsion of the nucleus pulposus into vertebral body through the endplate. This results in a burst fracture in which the fragments are displaced centrifugally. They are more common at the thoracolumbar
Curr Probl Diagn Radiol, September/October 2011
FIG 16. Vertical compression fracture in a 56-year-old male. (A) Sagittal reconstructed MDCT image shows the burst fracture of D12 vertebra with mild posterior displacement of the fracture fragment in to the spinal canal. (B) VRT clearly demonstrates the burst fracture of D-12 vertebra. (C) Coronal reconstructed MDCT image shows associated laminar split fracture in the same patient. (Color version of figure is available online.)
junction.17,18 Sagittal images demonstrate reduced anterior and posterior height of the vertebral body with posterior displacement of the posterior fragment into the spinal canal (Fig 16). Axial images show a comminuted fracture in the involved vertebra and associated laminar fracture if present. Signs of instability include widening of the interspinous and interlaminar distance, translation of more than 2 mm, kyphosis of more than 20 degrees, dislocation, height loss of more than 50%, and articular process fractures.8
Flexion Compression Injuries Flexion compression injuries are the most common thoracolumbar fractures. Sudden hyperflexion causes mechanical compression of the involved vertebra, resulting in anterior wedging of superior endplate.18 Posterior longitudinal ligament is intact in typical wedging. The typical anterior wedge fracture is stable as the middle column is preserved. Sagittal images show reduced anterior height of the vertebral body with preserved posterior vertebral body (Fig 17). Widening of the interspinous distance and focal kyphotic deformity indicates associated posterior ligamentous injury.
Curr Probl Diagn Radiol, September/October 2011
FIG 17. Flexion-compression fracture in a 39-year-old male. (A) Sagittal reconstructed image shows anterior wedging of L2 vertebra with relatively preserved posterior height. (B) Coronal reconstructed MDCT image shows typical wedging of L2 vertebra.
Shear Injury Shear injury is characterized by disruption of all 3 columns with anterior, posterior, or lateral displacement of the vertebra, depending on the direction of the force. The most frequent type is the anterior displacement of the vertebra with associated spinal cord injury. This is highly unstable and may be associated with visceral injuries.
Flexion—Distraction Injuries (Chance Fracture) This injury is caused by hyperflexion of the spine with distraction of the posterior elements (Fig 18). Chance fracture is common in automobile accidents when there is acute forward flexion of the spine across a restraining lap seatbelt during sudden deceleration (lap-belt fracture). The classic chance fracture is a horizontal fracture through the spinous process, laminae, pedicles, and vertebral body without any ligament injury. The chance variants include pure soft tissue injuries or combined bony-soft tissue injuries that may show horizontal split in the intervertebral disks and ligaments.
Hyper Extension Injuries Hyperextension injuries are extremely rare injuries and occur when there is a direct blow to the back or when the upper trunk is thrust backwards. These injuries are common in patients with ankylosing spon-
189
is now regarded as the primary investigation tool of choice.
REFERENCES
FIG 18. Chance fracture in a 48-year-old male. (A) Sagittal reconstructed MDCT image shows a horizontal fracture extending through the spinous process, pedicle, and vertebral body. (B) Volume-rendered (VRT) image shows the horizontal fracture extending through the vertebral body (arrow). (Color version of figure is available online.)
dylitis. It is characterized by compression/impaction of the posterior elements manifested by fractures (often comminuted) of the spinous process, lamina, or facets. In addition, there may be distraction of the anterior column manifested by anterior disk widening or avulsion fracture from the anterosuperior vertebral body. In severe injuries, there may be complete loss of continuity of upper and lower spinal segment resulting in paraplegia (lumberjack fracture-dislocation).
Transverse Process Fractures The mechanisms involved in these fractures include avulsion of the psoas muscle, lateral flexion-extension forces, or direct blunt trauma. These injuries may act as an indirect sign of associated abdominal visceral injuries or another spine fracture at a different level.
Conclusions Injuries to the spine result in significant mortality and morbidity. MDCT, with MPR and VRT reformations, is highly valuable for diagnosis, surgical planning, and management of spinal trauma. MDCT displays the complex anatomy of spine accurately and rapidly and thus accelerates the diagnostic process in spinal trauma victims. MDCT is the most sensitive method for imaging of osseous injuries in trauma patients and
190
1. Gonzalez-Beicos A, Nunez DB Jr. Role of multidetector computed tomography in the assessment of cervical spine trauma. Semin Ultrasound CT MR 2009;30:159-67. 2. American College of Radiology. Expert Panel on Musculoskeletal Imaging. Appropriateness criteria for suspected cervical spine trauma. ACR appropriateness criteria Available from: http://www.guideline.gov/summary/summary.aspx?doc_ id_8587. Reston, VA, 2002. 3. Geijer M, El-Khoury GY. MDCT in the evaluation of skeletal trauma: principles, protocols, and clinical applications. Emerg Radiol 2006;13:7-18. 4. Blackmore CC, Mann FA, Wilson AJ. Helical CT in the primary trauma evaluation of the cervical spine: an evidencebased approach. Skeletal Radiol 2000;29:632-9. 5. Li AE, Fishman EK. Cervical spine trauma: evaluation by multidetector CT and three-dimensional volume rendering. Emerg Radiol 2003;10:34-9. 6. Denis F. Three-column spine and its significance in classification of acute thoracolumbar spine injuries. Spine 1983;8: 817-32. 7. Bagley LJ. Imaging of spinal trauma. Radiol Clin North Am 2006;44:1-12. 8. Greenspan A. Spine. In: Greenspan A, editor. Orthopedic Radiology—A Practical Approach, 4th ed. New York: Lipincott Williams Wilkins, 2004. p. 349-410. 9. Anderson PA, Montesano PX. Morphology and treatment of occipital condyle fractures. Spine 1988;13:731-6. 10. Sherk HH. Fractures of the atlas and odontoid process. Orthop Clin North Am 1978;9:973-83. 11. Hays MB, Alker GJ Jr. Fractures of the atlas vertebra. The two-part burst fracture of Jefferson. Spine 1988;13:601-3. 12. Kesterson L, Benzel E, Orrison W, Coleman J. Evaluation and treatment of atlas burst fractures (Jefferson fractures). J Neurosurg 1991;75:213-20. 13. Effendi B, Roy D, Cornish B, et al. Fractures of the ring of the axis. A classification based on the analysis of 131 cases. J Bone Joint Surg 1981;63:319-27. 14. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg 1974;56:1663-74. 15. Ebraheim NA, Xu R, Ahmad M, et al. The effect of anterior translation of the vertebra on the canal size in the lower cervical spine: a computer-assisted anatomic study. J Spinal Disord 1997;10:162-6. 16. Campbell SE, Phillips CD, Dubovsky E, et al. The value of CT in determining potential instability of simple wedge-compression fractures of the lumbar spine. AJNR Am J Neuroradiol 1995;16:1385-92. 17. Stabler A, Eck J, Penning R, et al. Cervical spine: postmortem assessment of accident injuries—Comparison of radiographic, MR imaging, anatomic, and pathologic findings. Radiology 2001;221:340-6. 18. Dai LY. Imaging diagnosis of thoracolumbar burst fractures. Chin Med Sci J 2004;19:142-4.
Curr Probl Diagn Radiol, September/October 2011