DOI: 10.1148/rg.255045162
RadioGraphics 2005;25:1239-1254
© RSNA, 2005
Spectrum of Imaging Findings in Hyperextension Injuries of the Neck1
Sameet K. Rao, MD,
Christopher Wasyliw, MD and
Diego B. Nunez, Jr, MD, MPH
1 From the Department of Radiology, Hospital of Saint Raphael, Yale School of Medicine, New Haven, Conn. Recipient of a Certificate of Merit award for an education exhibit at the 2003 RSNA Annual Meeting. Received August 18, 2004; revision requested October 18 and received December 10; accepted January 27, 2005. All authors have no financial relationships to disclose.
Address correspondence to S.K.R., Department of Diagnostic Radiology, Section of Musculoskeletal Imaging, University of Maryland Medical Center, 22 S Greene St, Baltimore, MD 21201 (e-mail: schenger{at}hotmail.com).
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Abstract
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Nonphysiologic hyperextension and lateral forces acting on the cervical spine and soft-tissue structures of the neck can result in a wide spectrum of injury patterns. Multiple factors (eg, patient age; the underlying morphologic features of the cervical spine; the magnitude, vector, and maximal focus of the force) all influence the observed patterns and the severity of injury. A review of the 5-year trauma database in two trauma centers revealed various injury patterns that were frequently recognized in patients with clinical evidence or historical documentation of a predominant hyperextension mechanism. Injuries included anterior arch avulsion and posterior arch compression fractures of the atlas, odontoid fractures, traumatic spondylolisthesis and teardrop fracture of C2, laminar and articular pillar fractures, and hyperextension dislocation injuries. More severe injuries were observed in patients with underlying predisposing conditions (eg, degenerative spondylosis, ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis). Knowledge of the involved biomechanical factors provides a framework for understanding these injury patterns. Diagnostic imaging, especially computed tomography and magnetic resonance imaging, plays a fundamental role in the assessment of patients with suspected cervical injury. Furthermore, cross-sectional imaging facilitates the recognition of accompanying injuries to the face, the head, and the vascular structures of the neck.
© RSNA, 2005
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- Identify the various patterns of hyperextension injury to the osseous and soft-tissue structures of the neck.
- Discuss the role of various imaging modalities in recognizing and characterizing these hyperextension injuries.
- Describe conditions of the cervical spine that predispose to injury and identify extracervical injuries that are commonly associated with hyperextension trauma.
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Introduction
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Significant injuries to the spine and cervical soft tissues can result from physical forces that produce hyperextension of the neck. Injuries to the cervical spine occur when the load exceeds the physiologic range of backward motion or when extension produces anterior distraction and posterior compression. Rotational or lateral tilting forces may occur in combination with hyperextension, resulting in additional patterns of injury. Overall, hyperextension forces account for up to 38% of blunt traumatic injuries to the cervical spine (1).
A spectrum of traumatic lesions involving both osseous and soft-tissue structures of the neck are seen to occur in a relatively predictable pattern. In a smaller subset of patients, injuries may be limited to the soft tissues, particularly the ligaments and spinal cord. The severity of the injury depends on whether the mechanical stability of the spine or the integrity of the spinal cord has been compromised.
Radiography frequently provides direct and indirect evidence of injury but is often limited, especially in patients who are elderly or obese or who have sustained multiple trauma. Computed tomography (CT) is highly accurate for fracture detection and has been used as the primary modality in patients who have sustained multiorgan trauma or who cannot be adequately evaluated with clinical parameters and radiography. In addition, routine two-dimensional multiplanar reformation and three-dimensional (3D) imaging facilitate optimal characterization of the fracture. Magnetic resonance (MR) imaging provides optimal soft-tissue detail, thereby allowing direct evaluation of ligamentous and cartilaginous structures as well as of the spinal cord.
In this article, we review the biomechanical aspects of hyperextension and hyperextension-rotation trauma and the imaging evaluation of patients with suspected cervical spine injury. We also discuss and illustrate the variety of osseous, vascular, soft-tissue, and neurologic injuries that can be detected. We emphasize the role of imaging, especially multidetector CT and MR imaging, in identifying injury patterns and predicting the extent of lesions. In addition, we address the role of imaging in patients with underlying cervical spine abnormalities or associated extracervical injuries.
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Biomechanical Aspects of Hyperextension Trauma
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In the normal cervical spine, the ligamentous and capsular structures allow certain physiologic ranges of extension and lateral tilting. Traumatic injury to the cervical spine and associated soft-tissue structures occurs when these ranges are rapidly exceeded, as in trauma from high-speed motor vehicle accidents. Experiments with cadaveric specimens have shown that higher compressive loading rates are associated with lowering the threshold for injury and correlate with multilevel trauma as well (2). The age of the patient and the alignment of the cervical spine at the time of impact have also been shown to be important factors in cervical spine injury, independent of the loading rate (3,4).
Experimental studies have also demonstrated the degree of physiologic motion that occurs at specific levels in the cervical spine. In general, a range of 10°–20° occurs during flexion and extension, with the lower cervical spine demonstrating a greater degree of flexibility. Similarly, lateral tilting of 4°–12° is within the normal physiologic range, with the upper cervical spine demonstrating a greater degree of flexibility (4,5). When loading forces exceed the threshold of physiologic motion, failure of the osseous elements or supporting structures is observed, with resultant deformation and a spectrum of injury patterns (4).
Hyperextension injuries may result from either a direct contact mechanism or a noncontact mechanism (6). With direct contact, an impact to the forehead or face produces anterior distraction and posterior compression of the cervical spine. This type of injury is commonly seen in trauma caused by the forehead or face striking the dashboard or steering wheel in a motor vehicle accident. Hyperextension injuries to the cervical spine and spinal cord as well as to the brainstem have also been reported in unbelted patients from deployment of the air bag (7). In elderly patients, a fall from height may produce a high loading rate on a stiff spine to produce clinically significant injury (3,8). Athletic activities constitute an additional source of external loading forces, with resultant injury to the structures of the neck.
Noncontact hyperextension injuries to the neck are commonly referred to as whiplash injuries and result from unrestrained neck motion during a rear-end motor vehicle collision. An initial hyperextension component is followed by a flexion component, without impact to the head-neck complex. Although the magnitude of force in this mechanism is typically low, occult injuries not identified clinically or radiologically have been shown in experimental models (6).
Lateral tilting injuries most commonly occur in combination with hyperextension and are secondary to a rotational component at the time of impact. This combined hyperextension-rotation produces asymmetric vertical loading on the articular pillars on the side of rotation, which manifests as vertical or oblique fractures through the pillars at radiography (9).
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Imaging Evaluation
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The imaging evaluation of patients with suspected cervical spine injury has been extensively debated in the literature, mainly in terms of conventional radiography versus CT. Although radiography remains the initial study of choice in many patients with suspected injury, numerous fractures are missed or incompletely visualized, most frequently in the upper cervical spine, the cervicothoracic junction, and the posterior elements (10,11). Obtunded, elderly, or obese patients present additional challenges for image interpretation.
The use of CT, especially helical CT and, more recently, multidetector CT, in the setting of acute cervical trauma has gained widespread acceptance. CT has a high sensitivity and specificity and can be performed rapidly. Multiplanar reformation, 3D imaging, and CT angiography can be performed routinely and with minimal increase in study time. CT is especially useful in patients who have sustained multiple trauma, allowing rapid and comprehensive evaluation of multiple regions (12), often without the need for radiographic evaluation of the cervical spine. At many institutions (including our own), patients at high risk and those in whom CT is indicated to exclude injury in other body segments also undergo screening CT of the cervical spine. We use a four-channel multidetector CT scanner with the following standard protocol: 1-mm-thick axial images with a 3-mm reconstruction interval, a pitch of 1, a 6 mm/sec table speed, 120 kV, 220 mAs, and a 512 x 512 matrix. Reconstructed 1.5-mm-thick axial images with a 0.75-mm interval are used to generate routine coronal and sagittal reformatted images. CT angiography with intravenous bolus administration of contrast material is performed for evaluation of the vascular structures if clinical suspicion for injury is high.
In patients who present with a neurologic deficit after experiencing trauma, with or without osseous abnormalities at radiography or CT, MR imaging is the modality of choice. Gradient-echo and T2-weighted sequences are useful for revealing blood products and edema, respectively, within the cervical spinal cord. MR imaging also depicts ligamentous tears and disruptions, whose extent may be underestimated or which may not be evident at CT. MR angiographic evaluation of the neck vessels is also possible using time-of-flight or bolus angiographic techniques. However, the use of MR imaging in the acute setting is more restricted due to the limited availability of this modality and to its limited compatibility with the life support devices required in the critically ill patient. At our institution, imaging is performed using a dedicated cervical coil and a 256 x 256 matrix. Sagittal gradient-echo, inversion recovery, and T1- and T2-weighted images obtained at 3-mm intervals are used to evaluate the ligamentous structures and spinal cord for disruption as well as for edema or hemorrhage. We also routinely obtain axial T1-weighted and fat-saturated T2-weighted images at 3-mm intervals.
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Hyperextension Injuries
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Fractures of the Atlas
Fracture of the anterior arch from a hyperextension mechanism is typically a transverse fracture through the inferior pole or midportion, resulting from an avulsion mechanism. The injury occurs at the attachment site of either the atlantodental ligament or the longus colli muscles and is considered to be mechanically and neurologically stable.
The fracture is best visualized on the lateral radiograph as a lucent, irregular, noncorticated line through the anteroinferior pole of the arch, with variable separation of the fracture fragments. Localized prevertebral soft-tissue swelling is often present (Fig 1a). Although identification of this injury is typically straightforward, on occasion a nonunited secondary ossification center may appear similar to an anterior arch fracture. The presence of sclerotic margins and the absence of soft-tissue swelling should alert the person reading the images to this possibility. CT is not necessary when characteristic features of the fracture are seen at radiography but can be helpful in equivocal cases or when there is concern for other injuries (Fig 1b).
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Figure 1a. Anterior arch fracture. (a) Lateral radiograph shows cortical irregularity at the inferior aspect of C1 (arrow) with associated prevertebral soft-tissue swelling (arrowheads). (b) Sagittal reformatted image from CT data shows a transverse avulsion fracture of the inferior pole of C1 (arrow).
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Figure 1b. Anterior arch fracture. (a) Lateral radiograph shows cortical irregularity at the inferior aspect of C1 (arrow) with associated prevertebral soft-tissue swelling (arrowheads). (b) Sagittal reformatted image from CT data shows a transverse avulsion fracture of the inferior pole of C1 (arrow).
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Compression of the posterior arch of C1 between the occiput and spinous process of C2 as a result of hyperextension may result in a vertically oriented fracture of the posterior arch. As an isolated finding, posterior arch fracture is mechanically and neurologically stable. However, this fracture can also be part of a Jefferson burst fracture of C1 or associated with fractures of the dens. In a study by Levine and Edwards (13), more than one-half of patients with posterior arch fractures also had fractures in the second and third vertebral bodies.
An isolated posterior arch fracture may be radiographically occult or may be seen on the lateral radiograph as a lucent line through the posterior arch with no associated prevertebral soft-tissue swelling. Prevertebral soft-tissue swelling indicates a more complex injury. Because of the frequent association of posterior arch fractures with more severe injuries, CT is indicated in the evaluation of all patients with these fractures (Fig 2) (13,14).
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Figure 2. Posterior arch fracture. Three-dimensional volume-rendered (VR) image shows a nondisplaced fracture through the posterior arch of C1 (small arrow). An associated type 2 dens fracture with posterior displacement is also seen (large arrow).
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Fractures of the Axis
Fractures of the Dens.—
Fractures involving the dens are the most common injury of the axis, accounting for approximately 55% of fractures at this level (15). The injury may result from diverse mechanisms, including hyperextension. Anderson and D’Alonzo (16) classified fractures involving the dens into three types on the basis of the location of the fracture plane. Type 1 fracture is rare and controversial but is believed to represent avulsion of the tip of the dens from the attachment site of the alar ligaments. Type 2 fracture is the most common and consists of a transverse fracture through the base of the dens (Fig 3). The degree of displacement of the fracture fragment correlates directly with the prevalence of non-union, which may be as high as 50% (17). Type 3 fracture is a horizontal fracture through the superior body of the axis. This fracture is associated with a lower prevalence of nonunion due to the larger surface area of the fracture plane and the involvement of cancellous bone.
Radiographic detection of dens fractures depends on the degree of displacement and the presence of superimposed structures that complicate evaluation. Nondisplaced or impacted type 2 and type 3 fractures may be suspected only on the basis of prevertebral soft-tissue swelling on the lateral radiograph. Conversely, the fractures can be clearly seen on technically adequate open-mouth views. Disruption of the ring of C2 on the lateral radiograph is indicative of a type 3 dens fracture (Fig 4a). CT is essential for visualizing minimally displaced or impacted fractures in patients with prevertebral soft-tissue swelling and negative radiographic findings (Fig 4b). Because of the transverse fracture plane, axial images may be falsely negative, necessitating coronal and sagittal reformatted images to determine the presence and extent of injury.
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Figure 4a. Type 3 dens fracture. (a) Lateral radiograph shows a displaced type 3 dens fracture (large arrow) with disruption of the ring of C2 (small arrow). (b, c) Lateral radiograph (b) and coronal reformatted image from CT data (c) obtained in a different patient who had sustained traumatic injury show normal radiographic findings (b) and a nondisplaced type 3 dens fracture (arrows in c).
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Figure 4b. Type 3 dens fracture. (a) Lateral radiograph shows a displaced type 3 dens fracture (large arrow) with disruption of the ring of C2 (small arrow). (b, c) Lateral radiograph (b) and coronal reformatted image from CT data (c) obtained in a different patient who had sustained traumatic injury show normal radiographic findings (b) and a nondisplaced type 3 dens fracture (arrows in c).
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Figure 4c. Type 3 dens fracture. (a) Lateral radiograph shows a displaced type 3 dens fracture (large arrow) with disruption of the ring of C2 (small arrow). (b, c) Lateral radiograph (b) and coronal reformatted image from CT data (c) obtained in a different patient who had sustained traumatic injury show normal radiographic findings (b) and a nondisplaced type 3 dens fracture (arrows in c).
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Traumatic Spondylolisthesis.—
Traumatic spondylolisthesis (hangman fracture) is the second most common C2 fracture, accounting for approximately 23% of axis fractures (15). A direct impact to the face with hyperextension results in pathologic loading of the posterior aspect of the axis, producing bilateral vertically oriented fractures through the pars interarticularis (Fig 5). There is subsequent separation of the body and posterior arch of C2, which in and of itself results in decompression of the spinal canal. Effendi et al (18) proposed a classification system based on the presence of associated injuries that help determine mechanical and neurologic stability. An atypical variant of traumatic spondylolisthesis has been described, with either unilateral or bilateral fractures in the coronal plane through the posterior body of C2 (19). The identification of atypical traumatic spondylolisthesis is clinically relevant due to the greater degree of mechanical and potential neurologic deficit associated with this variant.
The typical and atypical forms of traumatic spondylolisthesis are both demonstrated on the lateral radiograph, with the fracture line extending through either the pars interarticularis (Fig 6) or the posterior body of C2. Widening of the C2-3 disk space and bilateral interfacetal dislocation may be seen, findings that indicate a more severe injury. CT is generally recommended to optimally demonstrate the location and orientation of the fracture planes, which are well seen at axial imaging (Fig 7). CT is especially useful in identifying atypical traumatic spondylolisthesis and in accurately characterizing the more complex injury patterns associated with this variant (Fig 8). Multiplanar reformatted images and 3D VR images are especially useful in this regard.
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Figure 8. Traumatic spondylolisthesis. Axial CT scan shows an oblique fracture through the posterior C2 body (long arrow), a finding that is consistent with atypical traumatic spondylolisthesis. Note the extension of the fracture to the right transverse process (short arrow).
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Hyperextension Teardrop Fracture
The teardrop-shaped fracture that results from hyperextension represents an avulsion of intact fibers of the anterior longitudinal ligament (ALL) off the anteroinferior endplate of the vertebral body. In elderly patients with osteoporosis, the fracture typically involves C2 due to fusion deformities in the lower cervical spine. A smaller degree of force is required to produce this injury in an underlying weak spine, with little or no soft-tissue swelling and no neurologic impairment. In younger patients, the avulsion most commonly occurs in the lower cervical spine, with extensive soft-tissue swelling and spinal cord injury that reflect the greater degree of traumatic force required to produce this injury. Neurologic manifestations are similar to those of hyperextension dislocation, with acute central cord syndrome seen in up to 80% of patients (20).
The lateral radiograph shows the triangular configuration of the fragment that has avulsed off the anteroinferior aspect of the vertebral body. The vertical dimension of the fragment is equal to or greater than its transverse dimension, which helps differentiate the avulsed fragment from the fragment seen in hyperextension dislocation (Fig 9). In elderly patients without soft-tissue swelling at conventional radiography, CT does not appear to provide significant additional information (14). However, in younger patients with a lower cervical hyperextension teardrop fracture and significant soft-tissue swelling at radiography, CT is required to better characterize the fracture and to evaluate for additional injuries. In addition, because of the high prevalence of associated acute cervical central cord syndrome, MR imaging is often performed to determine the presence and extent of spinal cord edema and contusion.
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Figure 9. Hyperextension teardrop fracture in a patient with underlying degenerative changes. Lateral radiograph shows a displaced triangular fracture fragment off the anteroinferior aspect of C2 (arrow).
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Hyperextension Dislocation
A severe hyperextension force to the face and neck can result in momentary posterior dislocation of the involved cervical vertebrae, producing injury predominantly to the cervical spinal cord and supporting soft-tissue structures. The ALL, annulus, intervertebral disk, and ligamentum flavum are disrupted. Stripping of the posterior longitudinal ligament (PLL) and tears of the paraspinal musculature are also present. An osseous component is seen in two-thirds of cases as a result of the avulsion of a nondisrupted annulus and Sharpey fibers off the anteroinferior endplate of the vertebral body (Fig 10) (9). Neurologic impairment is almost always present, with manifestations of acute central cord syndrome that vary from upper extremity paresthesias to complete quadriplegia.
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Figure 10. Drawing illustrates hyperextension dislocation. Note the fracture fragment resulting from avulsion by Sharpey fibers (arrow) as well as the disruption of ligamentous structures.
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Radiographic evaluation often leads to underestimation of the extent of hyperextension dislocation, showing normally aligned vertebrae due to immediate realignment following removal of the impacting force. The presence of diffuse prevertebral soft-tissue swelling with normally aligned vertebrae is the most reliable indicator of this injury (21). Widening of the disk space anteriorly and the presence of a vacuum disk are less frequently observed. The transverse dimension of the anteroinferior avulsion fracture fragment is characteristically greater than its vertical dimension, permitting differentiation from hyperextension teardrop fracture, whose triangular fragment has a greater vertical than transverse dimension (Fig 11).
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Figure 11. Hyperextension teardrop fracture. Lateral radiograph shows avulsion of the inferior endplate of C6 (arrowhead). The fact that the transverse dimension of the fracture fragment is greater than its vertical dimension increases the degree of suspicion for hyperextension dislocation.
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The extensive soft-tissue injury and spinal cord involvement are well depicted at MR imaging. The presence of ligamentous and disk disruption, along with hemorrhage and edema in the prevertebral space, are optimally demonstrated on sagittal MR images (Fig 12). High-signal-intensity edema and susceptibility artifact from hemorrhage within the spinal cord may accompany these findings, although isolated injury to the cord has also been observed (Fig 13).
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Figure 12a. Hyperextension dislocation. (a) Sagittal fat-saturated proton-density–weighted MR image shows disruption of the ALL at C5 (large arrow) with stripping of the PLL from the subjacent vertebral bodies (small arrow). (b) Sagittal proton-density–weighted MR image obtained in a different patient shows similar but less pronounced findings at the C3 through C4 level. Widening of the anterior disk space and posterior narrowing provide evidence of a hyperextension injury.
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Figure 12b. Hyperextension dislocation. (a) Sagittal fat-saturated proton-density–weighted MR image shows disruption of the ALL at C5 (large arrow) with stripping of the PLL from the subjacent vertebral bodies (small arrow). (b) Sagittal proton-density–weighted MR image obtained in a different patient shows similar but less pronounced findings at the C3 through C4 level. Widening of the anterior disk space and posterior narrowing provide evidence of a hyperextension injury.
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Figure 13a. Isolated injury to the cervical spinal cord from hyperextension dislocation. (a) Sagittal proton-density–weighted MR image shows high-signal-intensity edema in the spinal cord at the C7 through T1 level (arrow). (b) Sagittal gradient-echo MR image shows corresponding hemorrhage (arrow). No fractures or ligamentous injury was identified at CT or MR imaging.
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Figure 13b. Isolated injury to the cervical spinal cord from hyperextension dislocation. (a) Sagittal proton-density–weighted MR image shows high-signal-intensity edema in the spinal cord at the C7 through T1 level (arrow). (b) Sagittal gradient-echo MR image shows corresponding hemorrhage (arrow). No fractures or ligamentous injury was identified at CT or MR imaging.
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Laminar Fracture
Isolated fractures of one or both laminae are uncommon injuries that result from a hyperextension mechanism (9). Extension into the adjacent spinous process is frequently present. More commonly, the laminar disruption occurs as part of a burst fracture, pedicolaminar fracture-separation, or flexion teardrop fracture. The isolated fractures are mechanically stable, but neurologic sequelae may result from fragments within the cervical spinal canal (Fig 14).
Isolated laminar fractures may be difficult to visualize on the lateral radiograph, especially in the lower cervical spine, but may be seen as a lucent line in one or both laminae. CT is typically required to either identify or confirm the presence of the laminar fracture and to detect fragments within the spinal canal (14).
Hyperextension-Rotation Injuries
Simultaneous hyperextension and lateral tilting, producing axial loading on the side of rotation, classically results in an oblique or vertical fracture through the articular pillar (4,22). The fracture may be restricted to the pillar, with or without comminution (Fig 15). However, extension into adjacent structures, including the facets, transverse foramina, pedicles, and laminae, may occur (22).
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Figure 15a. Articular pillar fracture. (a) Axial CT scan through C6 shows a fracture through the left articular pillar (arrow). (b, c) Coronal reformatted (b) and sagittal 3D (c) images optimally show the vertical orientation of the fracture (arrow).
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Figure 15b. Articular pillar fracture. (a) Axial CT scan through C6 shows a fracture through the left articular pillar (arrow). (b, c) Coronal reformatted (b) and sagittal 3D (c) images optimally show the vertical orientation of the fracture (arrow).
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Figure 15c. Articular pillar fracture. (a) Axial CT scan through C6 shows a fracture through the left articular pillar (arrow). (b, c) Coronal reformatted (b) and sagittal 3D (c) images optimally show the vertical orientation of the fracture (arrow).
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Fracture through the pedicle and lamina may result in isolation and displacement of a free-floating articular pillar fragment, a condition that has been termed pedicolaminar fracture-separation injury. However, some authors have proposed that this condition is more commonly the result of a hyperflexion–lateral rotation injury (23). Neurologic impairment is not a typical feature of an isolated pillar fracture, but patients with pedicolaminar separation have a higher prevalence of neurologic deficits (23). Separation of the articular pillar is a mechanically unstable injury, often requiring surgical fixation (24). Mechanical instability may also occur with an isolated pillar fracture as a result of injury to the ALL and PLL, interspinous ligament, and facet capsule (4,25).
Isolated pillar fracture is often poorly visualized at radiography (26). Incongruity of the lateral margin of the pillar or a radiolucent line through the pillar on a frontal projection is suggestive of this injury (Fig 16a). On the lateral radiograph, the "double outline sign" resulting from posterior displacement of the fracture fragment has been described (27). CT is the modality of choice for identifying the fracture, determining fracture extension into adjacent structures, and assessing for the presence of a free-floating pillar fragment (Fig 16b) (26). If the articular pillar fracture is not isolated, its CT appearance alone is not predictive of subsequent instability, and the fracture may require surgical management rather than conservative treatment (25). In patients with subluxation at radiography or CT, ligamentous integrity is best evaluated with MR imaging (28). Increased T2 signal intensity in the facet capsule and ligamentous structures is consistent with injury and may help predict the development of instability in patients who receive conservative treatment only (25).
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Figure 16a. Articular pillar fracture. (a) Anteroposterior radiograph shows a fracture line (arrow) through the left articular pillar (*) with rotation of the fragment, producing the "bow tie" appearance. (b) Axial CT scan shows fracture and rotation of the left articular pillar (short arrows) as well as fracture of the ipsilateral lamina (long arrow).
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Figure 16b. Articular pillar fracture. (a) Anteroposterior radiograph shows a fracture line (arrow) through the left articular pillar (*) with rotation of the fragment, producing the "bow tie" appearance. (b) Axial CT scan shows fracture and rotation of the left articular pillar (short arrows) as well as fracture of the ipsilateral lamina (long arrow).
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Conditions Predisposing to Injury
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Patients with underlying abnormalities of the cervical spine are at increased risk for significant injuries, even from relatively minor forces. Elderly patients, especially those over 65 years of age, have a greater prevalence of injuries to the cervical spine owing to an increased propensity for falls and an increased per-mile risk of motor vehicle accidents (29). In addition, age-related degeneration, osteopenia, and spinal canal stenosis alter the mechanics of the cervical spine, lowering the threshold for injury (Fig 17) (30). A decrease in or loss of mobility affects the lower cervical spine to a greater degree, resulting in more frequent injury to the cervicocranium and upper spine, with fractures of the axis being the most common (Fig 18) (29). In addition, cervical spondylosis, spinal canal stenosis, and osteophyte formation occur in diffuse idiopathic skeletal hyperostosis syndrome, which predisposes to significant injury from a hyperextension mechanism.
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Figure 17a. Hyperextension injury in a patient with underlying spinal stenosis at the C5 through C6 level. The injury was caused by a fall forward onto the face. (a) Sagittal T2-weighted MR image shows spinal cord edema (short arrow). Edema within the intervertebral disk (arrowhead) and prevertebral soft-tissue edema (long arrow) are also seen. (b) Proton-density–weighted MR image shows tearing of the ALL (arrow).
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Figure 17b. Hyperextension injury in a patient with underlying spinal stenosis at the C5 through C6 level. The injury was caused by a fall forward onto the face. (a) Sagittal T2-weighted MR image shows spinal cord edema (short arrow). Edema within the intervertebral disk (arrowhead) and prevertebral soft-tissue edema (long arrow) are also seen. (b) Proton-density–weighted MR image shows tearing of the ALL (arrow).
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Figure 18a. Type 2 dens fracture in an elderly patient with underlying degenerative changes and osteopenia. Sagittal reformatted (a) and 3D VR (b) images show a posteriorly displaced type 2 dens fracture (arrow).
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Figure 18b. Type 2 dens fracture in an elderly patient with underlying degenerative changes and osteopenia. Sagittal reformatted (a) and 3D VR (b) images show a posteriorly displaced type 2 dens fracture (arrow).
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Patients with ankylosing spondylitis are also at increased risk for fractures of the cervical spine, which commonly result from hyperextension. The cervicothoracic junction is most frequently involved, with the fracture extending horizontally through the intervertebral disk to involve the entire spine at this level (Fig 19). Neurologic deficit may be present in approximately 60% of patients, with a mortality rate of approximately 35% in this patient subset (31).
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Figure 19a. Cervical spine fracture in a patient with ankylosing spondylitis. (a) Sagittal reformatted image shows a fracture through the intervertebral disk at the C7-T1 level (large arrow) with anterior displacement. Comminuted fracture of the posterior body of C7 is also seen (small arrow). (b) Sagittal reformatted image shows the fracture line extending posteriorly through the fused facet joint (arrow).
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Figure 19b. Cervical spine fracture in a patient with ankylosing spondylitis. (a) Sagittal reformatted image shows a fracture through the intervertebral disk at the C7-T1 level (large arrow) with anterior displacement. Comminuted fracture of the posterior body of C7 is also seen (small arrow). (b) Sagittal reformatted image shows the fracture line extending posteriorly through the fused facet joint (arrow).
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Associated Injuries
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Although injury to the vascular structures of the neck is more commonly the result of penetrating trauma, arterial injury may also occur in association with blunt hyperextension trauma (32,33). Stretching of the vessel during hyperextension or rotation causes intimal disruption, with resultant dissection or thrombotic occlusion. Pseudoaneurysm formation, vessel disruption, and arteriovenous fistulas are less common manifestations of arterial injury. Although digital subtraction angiography remains the standard of reference in the evaluation of arterial injury, both CT angiography and MR angiography can depict the luminal narrowing associated with dissection and the lack of flow associated with traumatic occlusion (12).
The vertebral artery is frequently injured as a result of either stretching of the vessel over bone or direct injury from fractures involving the transverse foramen (Fig 20). Recognition of this injury at initial CT is essential, since affected patients may be asymptomatic. In contrast, injury to the carotid artery is uncommon and is more readily recognized due to clinical symptoms (Fig 21).
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Figure 20a. Traumatic injury to the vertebral artery. (a) Unenhanced CT scan shows hyperattenuation in the left vertebral artery (arrow), a finding consistent with acute thrombus. (b, c) Three-dimensional image from CT angiographic data (b) and gadolinium-enhanced maximum-intensity-projection MR image (c) show occlusion of the entire left vertebral artery (arrowhead in c).
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Figure 20b. Traumatic injury to the vertebral artery. (a) Unenhanced CT scan shows hyperattenuation in the left vertebral artery (arrow), a finding consistent with acute thrombus. (b, c) Three-dimensional image from CT angiographic data (b) and gadolinium-enhanced maximum-intensity-projection MR image (c) show occlusion of the entire left vertebral artery (arrowhead in c).
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Figure 20c. Traumatic injury to the vertebral artery. (a) Unenhanced CT scan shows hyperattenuation in the left vertebral artery (arrow), a finding consistent with acute thrombus. (b, c) Three-dimensional image from CT angiographic data (b) and gadolinium-enhanced maximum-intensity-projection MR image (c) show occlusion of the entire left vertebral artery (arrowhead in c).
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Figure 21a. Traumatic injury to the carotid artery from hyperextension of the neck. (a) Contrast-enhanced CT scan shows narrowing of the lumen of the right internal carotid artery (ICA) (small arrow) with surrounding hematoma (large arrow). (b) Fat-saturated T1-weighted MR image shows narrowing of the ICA flow void (small arrow) with surrounding hyperintense intramural hematoma (large arrow). (c) Three-dimensional time-of-flight MR image shows narrowing of the cervical portion of the right ICA (arrows).
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Figure 21b. Traumatic injury to the carotid artery from hyperextension of the neck. (a) Contrast-enhanced CT scan shows narrowing of the lumen of the right internal carotid artery (ICA) (small arrow) with surrounding hematoma (large arrow). (b) Fat-saturated T1-weighted MR image shows narrowing of the ICA flow void (small arrow) with surrounding hyperintense intramural hematoma (large arrow). (c) Three-dimensional time-of-flight MR image shows narrowing of the cervical portion of the right ICA (arrows).
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Figure 21c. Traumatic injury to the carotid artery from hyperextension of the neck. (a) Contrast-enhanced CT scan shows narrowing of the lumen of the right internal carotid artery (ICA) (small arrow) with surrounding hematoma (large arrow). (b) Fat-saturated T1-weighted MR image shows narrowing of the ICA flow void (small arrow) with surrounding hyperintense intramural hematoma (large arrow). (c) Three-dimensional time-of-flight MR image shows narrowing of the cervical portion of the right ICA (arrows).
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Because hyperextension fractures and dislocations of the cervical spine commonly result from impact to the face and head, accompanying craniofacial and intracranial injury are frequently present (Figs 22, 23) (12). Injuries to the aerodigestive tract and other soft-tissue structures of the neck may also be recognized (Fig 24).
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Figure 23a. Spinal and craniofacial injuries sustained in a motor vehicle accident. The patient had not been wearing a seat beat. (a) Sagittal reformatted image from CT data shows a posteriorly displaced type 2 dens fracture (arrow). (b, c) Axial CT scans of the head show associated frontal soft-tissue hematoma (arrow in b) and a depressed nasal bone fracture (arrow in c) caused by the forehead and face striking the dashboard, with resultant hyperextension of the cervical spine.
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Figure 23b. Spinal and craniofacial injuries sustained in a motor vehicle accident. The patient had not been wearing a seat beat. (a) Sagittal reformatted image from CT data shows a posteriorly displaced type 2 dens fracture (arrow). (b, c) Axial CT scans of the head show associated frontal soft-tissue hematoma (arrow in b) and a depressed nasal bone fracture (arrow in c) caused by the forehead and face striking the dashboard, with resultant hyperextension of the cervical spine.
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Figure 23c. Spinal and craniofacial injuries sustained in a motor vehicle accident. The patient had not been wearing a seat beat. (a) Sagittal reformatted image from CT data shows a posteriorly displaced type 2 dens fracture (arrow). (b, c) Axial CT scans of the head show associated frontal soft-tissue hematoma (arrow in b) and a depressed nasal bone fracture (arrow in c) caused by the forehead and face striking the dashboard, with resultant hyperextension of the cervical spine.
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Figure 24a. Injury from direct blunt trauma to the anterior portion of the neck sustained in a motor vehicle accident. (a) Lateral radiograph shows anterior widening (large arrow) and posterior narrowing (small arrow) of the C6–7 disk space, with diffuse prevertebral hematoma. (b) Axial contrast-enhanced CT scan shows associated disruption of the right lobe of the thyroid gland (arrow).
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Figure 24b. Injury from direct blunt trauma to the anterior portion of the neck sustained in a motor vehicle accident. (a) Lateral radiograph shows anterior widening (large arrow) and posterior narrowing (small arrow) of the C6–7 disk space, with diffuse prevertebral hematoma. (b) Axial contrast-enhanced CT scan shows associated disruption of the right lobe of the thyroid gland (arrow).
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Conclusions
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Abstract
LEARNING OBJECTIVES FOR TEST...
