Injury Patterns in Vertebral Trauma

8/11/2019 Injury Patterns in Vertebral Trauma

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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 topredict 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 [14]. 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 [14].

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 Injuries

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

occur in four varieties: simple, burst, distraction, and dislocation [14, 7, 8].

Injury Patterns inVertebral TraumaRichard H. Daffner1


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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 occursalong 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 ismoved 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

D

Fig. 1Burst 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 superioraspect 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 Dshows sagittal cleavage through spinous process (arrow).

E

A CB


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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. 2Hyperflexion sprain in 22-year-oldman.A,Lateral radiograph shows slightanterolisthesis of C4 on C5 and widening ofinterlaminar space (asterisk).

B,T2-weighted MR image shows rupture ofposteriorlongitudinal ligament and diskherniation (arrow).

B

A C

Fig. 3Chance 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 andbelow this image (not shown) showed similar naked facets. Note fragmentation of pedicle on left.

B


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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 [14]. These find-

ings are summarized in Appendix 1.

Extension InjuriesExtension injuries occur in three distinct varieties: simple,

distraction, and dislocation [14, 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 hangmans 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 Injuries

Thoracolumbar 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. 4Unilateral facet lock at C5C6 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).

B


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A

C

Fig. 5Extension injuries in patients with rigid spinedisease.A,Lateral radiograph in 44-year-old man with ankylosingspondylitis shows widening of T9 disk space (asterisk). Noteanterior ankylosis and ky photic angulation at T11T12.B,Sagittal reconstructed CT image in same patient as inAshows wide disk space (arrow). Kyphotic angulation at

T11T12 is due to flexion injury at that level.C

and

D,Lateral radiograph (C) and sagittal reconstructedimage (D) in 72-year-old man with diffuse idiopathicskeletal hyperostosis (DISH) show widening of T8 disk space(asterisk). Wide disk space is hallmark of extension injury.

B

D

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 Injuries

Rotary 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, wherepatients 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, frequentlyposterior 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 C

Fig. 6Cervical 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 Bshows torn anterior disk space at C3 and significant cord hemorrhage ( arrow). These injuries typically producesevere central cord syndrome.

B


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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 agreater 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 Assessmentof Vertebral Stability

Stability of the vertebral column is defined as the ability of

the bones and ligaments that make up the column to protectthe 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

A

C

Fig. 7Shearing injury at L4L5 in 68-year-oldman.A,Frontal radiograph shows windsweptappearance of spine at L4L5. Note loss ofnormal anatomic boundaries between the twovertebrae.B,Lateral radiograph shows anterolisthesis of

L4 on L5. Note indistinctness of inferior marginof body of L4.CandD,Axial CT images show linearoblique distribution of bone fragments. Notetransverse process fracture on left. Windsweptappearance is characteristic of shearinginjuries.

B

D


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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 mayoccur 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

D

Fig. 8Rotary injury of L1 in 56-year-old man.A,Frontal radiograph shows severe disruption

of body of L1. Fracture extends through pedicleand transverse process on left (arrow).B,Lateral radiograph shows anterolisthesis of

T12 on L1. Note severe fragmentation of L1.C,Sagittal reconstructed CT image showsanterolisthesis (arrow) of T12 on L1. Note smallbone fragment from anterosuperior aspect ofL1 in its normal anatomic position.D,Axial CT image shows naked facet on leftside (arrow). Note concentric distribution ofbone fragments anteriorly.E,Axial CT image slightly lower showswidening of left facet (arrow).

E

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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.

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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 fracture

6. 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 fracturedislocation g. Occipitoatlantal dislocation or subluxation h. Atlantoaxial dislocation i. Anterior fracturedislocation of dens j. Lateral fracturedislocation of dens

2. Hyperextension a. Hangmans 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 Jeffersons 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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Injury Patterns in Vertebral Trauma