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State-of-the-Art Emergency and Trauma Radiology 45

Keywords: CT, mechanisms of injury, radiography, spine, trauma, vertebral injuries

1Department of Diagnostic Radiology, Allegheny General Hospital, 320 E North Ave., Pittsburgh, PA 15212-4772. Address correspondence to R. H. Daffner ([email protected]).

Vertebral injuries, like those to the peripheral skeleton, occur in a specific and predictable pattern that is strictly dependent on the mechanism of injury. The pattern may be easily recognized by the changes that the injury produces on imaging studies. These patterns are referred to as the “fingerprints” of the in-jury. Injuries due to a particular mechanism produce the same imaging changes regardless of the location. Recognizing the pattern of the injury allows one to predict the full extent of that injury.

All skeletal injuries occur in a specific and predictable pattern that is solely dependent on the mechanism of injury. Injuries to the vertebral column obey the same mechanical principles as those that occur in the peripheral skeleton. The pattern of the injury is recognizable by the radiographic or CT changes pro-duced. I refer to these patterns as the “fingerprints” of the injury [1–4]. Injuries due to any particular mechanism will produce the same radiographic changes regardless of the location. It matters not whether the injury has occurred in the cervical portion of the vertebral column or in the thoracic or lumbar regions. The changes due to a particular mechanism will be identical regardless of the location (cervical, thoracic, or lumbar). It is important to recognize the pattern because then it is easy to predict the full extent of that injury. The radiographic changes that an injury produces are typically referred to as the “footprints” of the injury. The fingerprints identify the extent of injury [1–4].

The diagnosis of vertebral injuries also relies on the same principles as those used for peripheral injuries. It is important to completely study the suspected bone(s) involved. In the peripheral skeleton, that means including the joint above and below all suspected levels of injury. The vertebral column, although consisting of 33 separate bones, functions as a single long bone. This means that to completely study the spine it is necessary to include all structures be-tween the skull and the sacroiliac joints (the joints above and below). This is of practical experience when one considers that multiple noncontiguous vertebral injuries occur in approximately 25% of patients [1].

Mechanisms of Injury and Their Radiographic FingerprintsThere are four basic mechanisms of vertebral injuries: flexion, extension,

shearing, and rotary. Shearing and rotary injuries are frequently associated with some degree of flexion. Flexion injuries occur throughout the vertebral column. Extension injuries occur primarily in the cervical region. Shearing and rotary in-juries typically occur in the thoracolumbar junction and lumbar region [5, 6].

Flexion InjuriesFlexion injuries are the most common injuries to the vertebral column; they

occur in four varieties: simple, burst, distraction, and dislocation [1–4, 7, 8].

Injury Patterns in Vertebral TraumaRichard H. Daffner1

46 2008 ARRS Categorical Course

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All are based on a similar mechanism. The type and extent of injury depends on the forces involved, including the degree of flexion and the amount of axial loading. The typical injury results from forward flexion when the fulcrum of motion is approximately through the posterior third of the intervertebral disk [1]. In the least severe injury, anterior compression occurs along the superior portion of the vertebral body immediately beneath the flexing vertebra. This produces anterior compres-sion of various degrees. Typically, the fracture line propagates posteriorly with or without communication to the interverte-bral disk space. These fractures are referred to as simple frac-tures and involve no injury to the posterior structures or to the posterior third of the disk.

With an increase in the flexion force or an increase in the degree of axial loading, the vertebra literally explodes, driv-ing fragments posteriorly into the vertebral canal to produce the burst fracture. A variant of this fracture occurs when the force is sufficient to split the vertebra sagittally, both anteriorly and posteriorly (Fig. 1). If the fulcrum of forward flexion is moved anteriorly, as occurs in individuals wearing a lap-type seat belt only, the primary injuring force is directed at the pos-terior structures, with rupture of the interspinous ligaments, facet ligaments, ligamenta flava, and, ultimately, the posterior longitudinal ligament.

Distraction injuries may take two forms. The first is severe posterior ligament damage with subsequent widening of the

DFig. 1—Burst fracture of L3 vertebra in 52-year-old woman.A, Lateral radiograph shows compression of superior aspect of L3 and displacement of bone fragment anteriorly. In addition, segment of superior aspect of posterior vertebral body line has been displaced posteriorly (arrow).B, Frontal radiograph shows widening of interpedicle space of L3 (double arrow).C, Sagittal reconstructed CT image shows this displaced fragment encroaching on vertebral canal (arrow).D, Axial CT image shows displaced fragment in vertebral canal (asterisk).E, Axial image slightly lower than D shows sagittal cleavage through spinous process (arrow).

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interlaminar (or interspinous) space. This pattern is typical of the hyperflexion sprain [1, 3] (Fig. 2). Alternatively, the frac-ture may extend in a horizontal fashion through the posterior elements and through the vertebral body to produce the so-called Chance-type fracture [9, 10] (Fig. 3). Finally, severely

forceful flexion injuries can produce a dislocation, which may occur with or without associated fractures.

Unilateral (Fig. 4) or bilateral facet locks occur as a result of flexion mechanisms. Anterolisthesis resulting from flexion injuries is always associated with widening of the interlaminar

A

Fig. 2—Hyperflexion sprain in 22-year-old man.A, Lateral radiograph shows slight anterolisthesis of C4 on C5 and widening of interlaminar space (asterisk).B, T2-weighted MR image shows rupture of posterior–longitudinal ligament and disk herniation (arrow).

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A CFig. 3—Chance fracture of L1 in 40-year-old man.A, Frontal view shows widening of interspinous space (asterisk). Note fracture through pedicle of L1 on left that extends into transverse process (arrow).B, Lateral radiograph shows anterior compression of L1 and posterior distraction.C, Axial CT image shows compression of anterior portion of vertebral body and “naked” facet on right side (arrow). Contiguous sections above and below this image (not shown) showed similar naked facets. Note fragmentation of pedicle on left.

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space, widening of the facet joints (including “naked” facets), and abnormal alignment of the spinolaminar line [1, 3].

Facet abnormalities are common in flexion injuries. Nor-mally, on a CT scan, the facet joints have the appearance of a hamburger. Unilateral or bilateral facet dislocations result in the “reverse hamburger bun” sign [11]. Naked facets may be easily recognized on CT scans as unopposed bony structures posteriorly, where one would normally expect to see the adja-cent vertebra. This appearance should never occur normally on more than one single slice.

Flexion injuries produce the following changes that may be seen on radiographs or on CT scans: compression, fragmenta-tion, and burst fractures of vertebral bodies; anterolisthesis; wide interlaminar space; “teardrop” fragments typically from the anteroinferior margin of the vertebral bodies; facet abnor-malities that include fractures or unilateral or bilateral blocks; an abnormal posterior vertebral body line [12]; and narrowing of the disk space above the level of injury [1–4]. These find-ings are summarized in Appendix 1.

Extension InjuriesExtension injuries occur in three distinct varieties: simple,

distraction, and dislocation [1–4, 13, 14]. Extension mecha-nisms are far more common in the cervical region but may be seen in the thoracic and lumbar regions. It is not rare to encounter the latter in patients with rigid spine disease (anky-losing spondylitis or diffuse idiopathic skeletal hyperostosis [DISH]) [15] (Fig. 5). Important cervical extension injuries include the hangman’s fracture of C2 and the extension sprain [1, 13, 14] (Fig. 6).

All extension injuries have in common disruption of the anterior longitudinal ligament with or without association of fracture and a varying degree of injury to the intervertebral disk. The most important imaging finding that may be seen on either radiographs or CT scans is widening of the disk space (Figs. 5 and 6). This finding is so important that whenever it is encountered, patients should be suspected of having an exten-sion injury through that level until proven otherwise. Other ra-diographic findings include small triangular avulsion fractures from the anterior disk margins of the vertebra either above or below the level of injury.

Retrolisthesis is typical in severe injuries. In a severe but rare form of extension injury, fractures occur through the neu-ral arch. Often these are associated with anterolisthesis. This may lead to some confusion because anterolisthesis is more typical of flexion injuries [1, 13, 14]. However, the mechanism should be clear when the anterolisthesis is accompanied by a normal spinolaminar line and normal interlaminar distance. These two anatomic landmarks are typically abnormal in the more common flexion-type of injury. Appendix 2 summarizes the fingerprints of extension injury.

Shearing InjuriesThoracolumbar injuries typically cluster between T11 and

L2. The reason for this is the facet reorientation that occurs from the coronal plane to the sagittal plane. Indeed, at L1, the facet joints are oriented at 90°, which strongly resists any kind of side-to-side or rotary motion [16]. In addition, the change from the kyphotic thoracic curve to the lordotic lumbar curve and the loss of the stabilizing effects of the ribs increase the

A CFig. 4—Unilateral facet lock at C5–C6 in 73-year-old woman.A, Lateral radiograph shows anterolisthesis of C5 on C6 (arrow). Note widening of interlaminar space (asterisk).B, Axial CT image shows locked facet on right (arrow). Note that appearance is that of a reversed hamburger bun.C, Sagittal reconstructed CT image shows facet lock (arrow).

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Fig. 5—Extension injuries in patients with rigid spine disease.A, Lateral radiograph in 44-year-old man with ankylosing spondylitis shows widening of T9 disk space (asterisk). Note anterior ankylosis and kyphotic angulation at T11–T12.B, Sagittal reconstructed CT image in same patient as in A shows wide disk space (arrow). Kyphotic angulation at T11–T12 is due to flexion injury at that level.C and D, Lateral radiograph (C) and sagittal reconstructed image (D) in 72-year-old man with diffuse idiopathic skeletal hyperostosis (DISH) show widening of T8 disk space (asterisk). Wide disk space is hallmark of extension injury.

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mechanical vulnerability of the region to all de-grees of motion.

Shearing injuries are the result of horizontal or obliquely directed forces with associated for-ward or lateral flexion [1, 3, 5, 6, 13]. The most common cause that we encounter in our practice is ejection from a motor vehicle in which the indi-vidual strikes the upper or lower part of the body while the other half of the body continues moving in the same direction as the initial ejection. The result of shearing injuries is a pattern that is quite different from that seen with either flexion or ex-tension injuries.

Shearing injuries typically produce imaging features of lateral distraction and lateral disloca-tion. The vertebrae may have a windswept appear-ance (Fig. 7). In addition, this mechanism produces transverse process or rib fractures. Anterolisthesis is also typically present. Lateral fragmentation that is linear in the direction of the deforming force may be seen on a CT scan (Fig. 7C).

The importance of recognizing shearing frac-tures is that the injury initially may resemble a burst fracture. Because these injuries are typically unstable (see the following text), the treatment is radically different. Treatment of burst fractures is directed at providing stability along the sagit-tal plane. Treatment of shearing injuries must be directed toward reestablishing stability not only in the sagittal plane but also in the oblique planes.

It is not difficult to differentiate shearing inju-ries from burst fractures when one knows the typi-cal signs produced by each. Shearing injuries typi-cally have a greater degree of lateral displacement and a tendency for lateral dislocation. Transverse process or rib fractures are also hallmarks of this injury (and of rotary injuries). Furthermore, the linear oblique and windswept appearance on both radiographs and CT scans is also typical. Burst fractures, on the other hand, have little tendency to dislocate, even along the sagittal plane. If the


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vertebra has been split along the sagittal plane, there will be widening of the interpedicle distance reflecting that (Fig. 1). Finally, on CT, there is a linear sagittal distribution of frag-ments [1, 3]. The fingerprints of shearing injuries are listed in Appendix 3.

Rotary InjuriesRotary injuries may be seen in two locations. The most com-

mon location is at the thoracolumbar junction. Once again, the unique anatomy of that region sets the stage for these injuries to occur when the right mechanism is applied [16]. The second location for rotary injuries is the atlantoaxial region, where patients may suffer a pure ligamentous injury referred to as atlantoaxial rotary subluxation or frank dislocation in atlanto-axial rotary fixation [17]. Rotary injuries to the thoracolumbar region are most frequently the result of motor vehicle crashes in which an individual is ejected. The mechanism of injury is an obliquely directed force to the upper torso with twisting of the lower torso accompanied by lateral deflection. There is generally some degree of forward or lateral flexion in addition to the twisting mechanism [1, 3].

The imaging findings of rotary injuries are distinct and sug-gestive. There is severe fragmentation of the vertebral body. Often, a fragment of bone from the inferior vertebra is torn from the anterosuperior margin of the vertebral body (Fig. 8). Because of the severe fragmentation, the vertebra is frequent-ly pulverized, leading to the designation of these injuries as “grinding.” Disruption of the posterior vertebral body line of-ten leads to this injury being confused with burst fractures. Consequently, there is canal encroachment. Like shearing injuries, transverse process or rib fractures typically occur. These features alone serve to differentiate this injury from burst fractures. There is usually anterolisthesis, frequently posterior distraction, and facet distraction. On CT, the bone fragments are displayed in a circular or concentric fashion. Because of the rotary mechanism, one facet joint is displaced anteriorly and the other is displaced posteriorly, allowing the viewer to determine the exact direction in which the rotation occurred (Fig. 8C).

As with shearing injuries, it is important to differentiate rotary injuries from burst fractures because the treatment is different. Treatment of burst fractures, as previously mentioned,

A CFig. 6—Cervical extension sprains.A, Lateral radiograph shows widening of C5 disk space (asterisk) in 76-year-old man. Note small avulsed bone fragment from anteroinferior margin of C5 (arrow).B, Lateral radiograph in 62-year-old man shows widening of C3 disk space (asterisk) and retrolisthesis of C3 on C4.C, Autopsy specimen from patient in B shows torn anterior disk space at C3 and significant cord hemorrhage (arrow). These injuries typically produce severe central cord syndrome.

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is directed to reestablishing stability in the sagittal plane. On the other hand, treatment of rotary injuries is directed to re-establishing stability in the sagittal, axial, and coronal planes. Rotary injuries have a greater degree of separation and a greater tendency to dislocate. Transverse process or rib frac-tures are characteristic. Most characteristic is the concentric distribution of the bone fragments on a CT. On MRI, the soft-tissue injury from rotary mechanisms is much more exten-sive. Burst fractures, on the other hand, have little tendency to dislocate. They may have widening of the interpedicle dis-tance, and, on CT, have a linear and sagittal distribution of bone fragments. The fingerprints of rotary injury are listed in Appendix 4.

Radiographic Assessment of Vertebral Stability

Stability of the vertebral column is defined as the ability of the bones and ligaments that make up the column to protect the spinal cord under normal function [1, 18, 19]. Stability de-pends on the integrity of certain anatomic structures that will not permit excessive motion to allow compromise of either the spinal cord or the nerves. In 1983, Denis [20] created the concept of the three-column spine. He defined the anterior col-umn as those structures beginning at the anterior longitudinal ligament and extending posteriorly to an imaginary line ap-proximately two thirds of the way through the vertebral body and intervertebral disk. The middle column extended from that

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Fig. 7—Shearing injury at L4–L5 in 68-year-old man.A, Frontal radiograph shows windswept appearance of spine at L4–L5. Note loss of normal anatomic boundaries between the two vertebrae.B, Lateral radiograph shows anterolisthesis of L4 on L5. Note indistinctness of inferior margin of body of L4.C and D, Axial CT images show linear oblique distribution of bone fragments. Note transverse process fracture on left. Windswept appearance is characteristic of shearing injuries.

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line to the posterior longitudinal ligament. The posterior col-umn extended from the posterior longitudinal ligament to the supraspinous ligament. Denis was able to show, through bio-mechanical experiments, that the integrity of the middle col-umn was key to overall anatomic stability in the spine. From a practical standpoint, disruption of two contiguous zones (an-terior and middle columns or middle and posterior columns) produced instability. Disruption of a single column (anterior or posterior) did not result in instability.

What, then, are the radiographic signs of instability? There are five, and they may be seen on radiographs, CT, or MRI: displacement, widening of the interlaminar (interspinous) space, widening of the facet joint, widening of the interpedicle distance, and an abnormal posterior vertebral body line [1, 18, 19]. Displacement (Fig. 8) generally results in disruption of all

three columns. Widening of the interlaminar space and widen-ing of the facet joint are the result of disruption posteriorly (Fig. 2). Unless the posterior third of the disk has been torn, widening of the interlaminar space cannot occur, nor can facet joint wid-ening. Widening of the interpedicle distance indicates that the vertebra has been split along the sagittal plane (Fig. 1). This may occur with or without an intracanalicular displaced fragment. Finally, an abnormality of the posterovertebral body line (Fig. 1) indicates a disruption to the posterior third of the vertebra and the disk. This may occur from a variety of mechanisms.

Although most of these signs of instability occur in combi-nation with one another, the presence of only one is sufficient to make the diagnosis [1, 18, 19]. Indeed, the presence of these signs also indicates that the patient has suffered a major injury. Major injuries are defined as those that produce neurologic

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Fig. 8—Rotary injury of L1 in 56-year-old man.A, Frontal radiograph shows severe disruption of body of L1. Fracture extends through pedicle and transverse process on left (arrow).B, Lateral radiograph shows anterolisthesis of T12 on L1. Note severe fragmentation of L1. C, Sagittal reconstructed CT image shows anterolisthesis (arrow) of T12 on L1. Note small bone fragment from anterosuperior aspect of L1 in its normal anatomic position. D, Axial CT image shows naked facet on left side (arrow). Note concentric distribution of bone fragments anteriorly.E, Axial CT image slightly lower shows widening of left facet (arrow).

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deficits or have the potential to do so, or produce instability or have the potential to do so. They require surgical intervention. Minor injuries, on the other hand, require only symptomatic and supportive treatment. Examples of major injuries are burst fractures, rotary (grinding) injuries, and shearing injuries. Ex-amples of minor injuries are spinous process fractures, isolat-ed articular pillar fractures, and simple compression fractures [21]. Appendix 5 is a more complete compendium of major injuries, and Appendix 6 lists minor injuries. Although this concept was developed for cervical injuries, the principles are identical for thoracic and lumbar injuries as well.

ConclusionVertebral injuries occur in a predictable pattern that depends

on the mechanism of injury. That pattern constitutes the finger-prints of the injury. The imaging findings, or fingerprints from any particular mechanism, are identical no matter where they occur in the vertebral column. It is important to recognize the types of injuries because the treatment will be radically differ-ent for each type.

REFEREnCES1. Daffner RH. Imaging of vertebral trauma, 2nd ed. Philadelphia, PA: Lippincott-

Raven, 1996:95–1422. Daffner RH, Daffner SD. Vertebral injuries: detection and implications. Eur J

Radiol 2002; 42:100–1163. Daffner RH, Daffner SD. Vertebral injuries: detection and implications. In:

Cassar-Pullicino VN, Imhoff H, eds. Spinal trauma: an imaging approach. Stuttgart, Germany: Thieme, 2006:81–99

4. Daffner RH, Deeb ZL, Rothfus WE. “Fingerprints” of vertebral trauma: a unifying concept based on mechanisms. Skeletal Radiol 1986; 15:518–525

5. Denis F, Burkus JK. Shear fracture–dislocations of the thoracic and lumbar spine associated with forceful hyperextension (lumberjack paraplegia). Spine 1992; 17:156–161

6. Jeanneret B, Ho PK, Magerl F. Burst–shear–flexion–distraction injuries of the lumbar spine. J Spinal Disorders 1993; 6:473–481

7. Allen BL Jr, Ferguson RL, Lehmann TR, et al. A mechanistic classification of closed, indirect fractures and dislocations of the lower cervical spine. Spine 1982; 7:1–27

8. Ferguson RL, Allen BL Jr. A mechanistic classification of thoracolumbar spine fractures. Clin Orthop Rel Res 1984; 189:77–88

9. Chance GQ. Note on a type of flexion fracture of the spine. Br J Radiol 1948; 21:452–453

10. Smith WS, Kaufer H. Patterns and mechanisms of lumbar injuries associated with lap seat belts. J Bone Joint Surg Am 1969; 51:239–254

11. Daffner SD, Daffner RH. Computed tomography diagnosis of facet dislocations: the “hamburger bun” and “reverse hamburger bun” signs. J Emerg Med 2002; 23:387–394

12. Daffner RH, Deeb ZL, Rothfus WE. The posterior vertebral body line: importance in the detection of burst fractures. AJR 1987; 148:93–96

13. Gehweiler JA Jr, Osborne RL Jr, Becker RF. The radiology of vertebral trauma. Philadelphia, PA: Saunders, 1980

14. Holdsworth FW. Fractures, dislocations, and fracture–dislocations of the spine. J Bone Joint Surg Am 1970; 52:1534–1551

15. Hendrix RW, Melany M, Miller F, et al. Fracture of the spine in patients with ankylosis due to diffuse skeletal hyperostosis: clinical and imaging findings. AJR 1994; 162:899–904

16. White AA III, Panjabi MM. Clinical biomechanics of the spine, 2nd ed. Philadelphia, PA: Lippincott, 1990

17. Fielding JW, Hawkins RJ. Atlanto-axial rotary fixation: fixed rotatory subluxation of the atlanto-axial joint. J Bone Joint Surg Am 1977; 59:37–44

18. Gehweiler JA Jr, Daffner RH, Osborne RL Jr. Relative signs of stable and unstable thoracolumbar vertebral trauma. Skeletal Radiol 1981; 7:179–183

19. Daffner RH, Deeb ZL, Goldberg AL, et al. The radiologic assessment of post-traumatic vertebral stability. Skeletal Radiol 1990; 19:103–108

20. Denis F. The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983; 8:817–831

21. Daffner RH, Brown RR, Goldberg AL. A new classification for cervical vertebral injuries: influence of CT. Skeletal Radiol 2000; 29:125–132

APPEnDIX 1: “Fingerprints” of Flexion Injuries

1. Compression, fragmentation, burst of vertebral bodies2. “Teardrop” fragments3. Anterolisthesis4. Disrupted posterior vertebral body line5. Wide interlaminar (interspinous) space6. Locked facets7. Narrow disk space above involved vertebra

APPEnDIX 2: “Fingerprints” of Extension Injuries

1. Wide disk space below involved vertebra2. Triangular avulsion fracture anteriorly3. Retrolisthesis4. Neural arch or pillar fracture5. Anterolisthesis with normal interlaminar space and spinolaminar line

APPEnDIX 3: “Fingerprints” of Shearing Injuries

1. Windswept appearance2. Lateral distraction3. Lateral dislocation4. Transverse process or rib fracture5. Linear oblique (windswept) array of fragments on CT

APPEnDIX 4: “Fingerprints” of Rotary Injuries

1. Rotation2. Dislocation3. Disrupted posterior vertebral body line4. Facet or pillar fracture or dislocation5. Transverse process or rib fracture6. Spinous process fracture7. Rotary array of fragments on CT


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APPEnDIX 5: Major Injuries

1. Hyperflexion a. Hyperflexion sprain b. Hyperflexion dislocation (1) Without facet lock (2) With unilateral or bilateral facet lock c. Comminuted (“teardrop”) body fracture d. Burst fracture e. Chance-type fracture f. Hyperflexion fracture–dislocation g. Occipitoatlantal dislocation or subluxation h. Atlantoaxial dislocation i. Anterior fracture–dislocation of dens j. Lateral fracture–dislocation of dens

2. Hyperextension a. Hangman’s fracture b. Hyperextension sprain c. Hyperextension dislocation d. Posterior atlantoaxial dislocation

3. Shearing injury a. Thoracolumbar shear injury

4. Rotary injury a. Rotary atlantoaxial dislocation (fixation) b. Rotary atlantoaxial subluxation c. Rotary (“grinding”) thoracolumbar injury

5. Cervical axial compression a. Bursting Jefferson’s fracture b. Vertical and oblique fractures of axis body c. Occipital condyle type 3 fracture

APPEnDIX 6: Minor Injuries

1. Hyperflexion a. Spinous process fracture b. Wedge-like compression of body (simple fracture) c. Transverse process fracture (isolated) d. Uncinate process fracture (isolated) e. Articular pillar fracture (isolated) f. Laminar fracture g. Lateral wedge fracture of body

2. Hyperextension a. Horizontal fracture of anterior arch of atlas b. Anterior inferior margin of C2 (“teardrop”) c. Spinous process fracture d. Posterior arch of atlas fracture (isolated)

3. Shearing injury— None

4. Rotary injury — None

5. Axial compression a. Lateral mass of atlas (isolated) b. Occipital condyle types 1 and 2 fractures

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