Radiographically subtle soft tissue injuries of the cervical spine

John H. Harris, Jr., M.D., D&z., obtained his degree in medicine from Thomas Jefferson University, Philadelphia in 1953 and completed his radiology residency at the Hospital of the University of Pennsylvania in 1957, during which time he also earned the MSc. and D.Sc. degrees from the University of Pennsylvania Graduate School of Medicine. Dr. Harris had a private practice in radiology in Carlisle, Pennsylvania from 1957 to 1979, during which time he held clinical appointments in radiology at the Hospital of the University of Pennsylvania and at Thomas Jefierson University. He served on the faculty of the Michigan State University School of Medicine from 1979 until 1980, when he joined the faculty of the University of Texas Health Science Center at Houston KITHSC-HI as Chief of Emergency Radiology in Hermann Hospital. In 1982 he was appointed Professor and Chairman of the Department of Radiology at UTHSC-H and Radiologist-in-Chief at Hermann Hospital, positions which he holds curren tly.

Joel W. Yeakley, M.D., received his M.D. degree from the University of Texas Medical Branch in Galveston in 1965. He completed his internship at Los Angeles County Harbor General Hospital, 2965 to 1966. Afler completing a residency in neurology at the University of Florida in 1973, he was a resident in radiology at that same institution from 1973 to 1976. Dr. Yeakley completed a Fellowship in Neuroradiology at the University of Te,xas Medical School in Houston, 1982 to 1983. Dr. Yeakley is presently Associate Professor of Radiology and Chief of Neuroradiology at the University of Texas Medical School, Hermann Hospital in Houston. 166

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RADIOGRAPHICALLY SUBTLE SOFT TISSUE INJURIES OF THE CERVICAL SPINE*

The purpose of this presentation is to describe and illustrate, as completely as possible, the current understanding of two relatively common cervical spine injuries that are radiographically subtle, poorly understood by many radiologists and, when not recognized, associated with major adverse medical consequences. The injuries to be discussed are anterior subluxation (a hyperflexion injury) and hyperextension dislocation (a hyperextension injury). The pathophysiologic feature common to both anterior subluxation and hyperextension dislocation is that each is a soft tissue injury. The radiographic feature common to each is that their recognition depends on soft tissue changes on the lateral radiograph of the cervical spine. In anterior subluxation, there is widening of the interlaminar and interspinous spaces at the level of the ligamentous injury; in hyperextension dislocation, there is diffuse prevertebral soft tissue swelling caused by hemorrhage and/or edema secondary to disruption of prevertebral soft tissues in the causative hyperextension. Each of these injuries is well recognized by the majority of orthopedic and neurologic surgeons, a result of extensive docuementation in their literature. The radiologist involved in the early management decision-making process regarding patients sustaining acute cervical spine trauma has the responsibility of providing the formal interpretation of the radiographic examinations, including those *Supported Foundation.

in part

by a grant

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the

John

S. Dunn

obtained on patients who have anterior subluxation or hyperextension dislocation. It is, therefore, incumbent upon radiologists to be completely conversant with all of the radiologic manifestations of these injuries and to be cognizant of their clinical presentations, pathophysiology, and complications.

~~RIORSUBL~~ATI~N(HW~FLEXION SPRAIN) GENERAL Anterior subluxation (hyperflexion sprain) results from tearing of the posterior ligament complex and is one of the hyperflexion “family” of injuries (Table 1). Many radiologists, however, held in disrespect or frankly rejected the radiographic diagnosis of anterior subluxation of the cervical spine until precise and accurate descriptions of its roentgen signs appeared in the recent literature.lP3 Referring to anterior subluxation as “hyTABLE HVperflexion

1. Injuries*

Flexion Anterior subluxation (hyperflexion sprain) Bilateral interfacetal dislocation Simple wedge (compression) fracture Clay-shoveler (coal shoveler) fracture Flexion teardrop fracture ‘From Harris JH Jr, Ed&ken-Monroe B, Kopaniky OR: Orthop Clin North Am 1986; 17:15-30. Used by permission.

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perflexion sprain,” Braakman and Penning4 prepared a classic and detailed description of this injury in 1968. Anterior subluxation has long been recognized by orthopedists and neurosurgeons.5-g Stringa, lo Holdsworth,l’ and Selecki5 described the mechanism of injury and the pathophysiology of the lesion in great detail. Cheshire” reported 21% delayed instabiliy following anterior subluxation, as against 5% to 7% delayed instability associated with all other types of cervical spine injuries. It is currently estimated that the incidence of delayed instability following anterior subluxation may be as high as 50%. Jackson7 cited the development of localized degenerative changes following anterior subluxation as evidence of soft tissue trauma at the time of injury. Tear of the posterior ligament complex may occur either as an isolated injury (anterior subluxation, hyperflexion sprain) or as an integral component of any cervical spine injury in which flexion is a major vector force. MECHANISM OF INJURY AND PATHOPHYSIOLOGY Anterior subluxation is caused by a flexion force of less than 490 kg/cm2.5 The pathophysiology of anterior subluxation consists of disruption of the

posterior ligament complex (the supraspinous and interspinous liagments, the interfacetal joint capsules, the ligamenturn flavum, and the posterior longitudinal ligament.)5-11 The posterior portion of the annulus fibrosis and, to varying degrees, the posterior aspect of the intervertebral disc, are torn while the greatest part of the disc and the anterior portion of the annulus as well as the anterior longitudinal ligament remain intact (Fig 1). As a result of disruption of the posterior ligament complex, the vertebra immediately above the level of the soft tissue injury may (1) rotate anteriorly pivoting on its anterior inferior corner, or (2) glide (translate) anteriorly with respect to the immediately subjacent vertebra. In the latter instance the annulus, anteriorly, and the anterior longitudinal ligament are stretched but not disrupted. The pathology of anterior subluxation, in which the subluxated vertebra is anteriorly displaced, is schematically represented in Fig. 2. This figure illustrates the concept of anterior subluxation as described by Holdsworth,= with minimal (1 to 3 mm) anterior displacement of the involved vertebra and consequent subluxation, but not@ank dislocation of the intervertebral joints. Because the skeletal stability provided by the normal anatomy of the interfacetal joints is maintained, although subluxated, and because the intervertebral disc is not completely disrupted and the anterior longitudinal ligament remains intact, anterior subluxation is considered to be initially mechanically stable.

FIG 1. Schematic drawing of the pathology of anterior subluxation. a indicates the supraspinous ligament; b indicates the interspinous ligament; c indicates the apophyseal joint capsule; and d indicates the posterior longitudinal ligament. The ligamentum flavum is not represented. 168

FIG 2. Schematic representation of anterior subluxation the posterior ligament complex and very slight of the subluxated vertebra according to the worth.” Curr

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FIG 3. A, lateral radiograph demonstrating (B) demonstrates diffuse reversal

RADIOGRAPHIC

normal cervical of lordosis.

lordosis.

The

lateral

DIAGNOSIS

Whitley and Forsyth13 described some of the radiologic signs of “partial dislocation” (anterior subluxation) in 1960. However, the radiologic signs of anterior subluxation were neither accurately nor completely described until 1978,14 and subsequently in 198015 and 1981.l Prior to 1978,16 the radiologic signs of anterior subluxation were described as “reversal of normal cervical lordosis,” or “straightening of the cervical spine .” Approximately 17% of the normal adult population has some degree of straightening or reversal of cervical lordosis. Normal cervical lordosis (Fig 3,A) is physiologically reversed in the “military” or “chin-on-chest” position (see Fig 3,B) It is frequently reversed in the supine position (Fig 41 and may also be reversed by muscle spasm (Fig 51. It is clear, therefore, that simple reversal of cervical lordosis could not reliably be used as the radiologic sign of anterior subluxation. Physiologic reversal of cervical lordosis in flexion is a continuous uninterrupted kyphosis throughout the cervical area, greater in the upper than in the lower cervical segments as the translation of each segment increases at each successively higher level (Fig 6). Forward translation of individual cervical vertebrae occurs physiologically in one of two distinct patterns. In one instance, the cervical straightenCur-r Probl

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cervical

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ing or lordotic reversal occurs as a smooth, uninterrupted continuum from C7 through Cl (see Fig 6). In the second pattern, each cervical vertebra appears to translate anteriorly as a separate independent unit with each successively higher vertebra moving anteriorly at a proportionately greater distance in a “step-wedge” configuration (Fig 7). It is critically important to realize that forward translation of one cervical segment with respect to its subjacent member may be as much as 4 mm, physiologically. This observation has been clearly demonstrated experimentally by White and Panjabi.r7 Such intervertebral movement is, therefore, normal and physiologic and, when part of a continuum of flexion, must not be interpreted as pathologic subluxation. The radiographic signs of anterior subluxation are (1) a localized kyphotic angulation at the level of injury; (2) anterior rotation, with or without anterior displacement, of the subluxated vertebra; (3) anterior narrowing and posterior widening of the disc space; (4) widening of the space between the subluxated vertebral body and the subjacent articular masses; (5) displacement of the inferior articulating facets of the subluxated vertebra with respect to their contiguous subjacent facets and incongruity of the facets; and (6) widening of the interspinous or interlaminar space (“fanning”) .l Careful evaluation of the lateral radiograph in neutral, flexion, and extension positions with strict 169

FIG 4. Physiologic

reversal

of cervical

lordosis

in recumbent

position.

FIG 5. Diffuse reversal of cervical lordosis secondary to muscle associated with the clay-shoveler’s fracture of C6.

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FIG 6. Lateral radiograph demonstrating the typical appearance of the cervical spine in flexion. The reversal of normal lordosis is smoothly continuous throughout the cervical spine with progressively greater anterior rotation of the vertebrae at each successively higher segment from C7 through C3.

adherence to the criteria of anterior subluxation are necessary to minimize “over-reading.” For example, the patient illustrated in Figure 8 was the passenger in an automobile that was struck from behind. She complained of severe, diffuse pain and

moderate limitation of motion ir, the cervical area. There were no localizing nourologic signs or symptoms. In the neutral lateral radiograph, the normal cervical lordotic curve is uniformly and smoothly reversed throughout the length of the

FIG 7. Lateral radiograph the physiologic segments which

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of a normal adult cervical “step-wedge” relationship may occur in flexion.

spine demonstrating of adjacent vertebral

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FIG 8. A, lateral

radiograph of the cervical spine sion (C) cervical radiographs demonstrate cludes anterior subluxation

demonstrating only normal,

smooth, physiologic

continuous reversal of cervical lordosis. Lateral flexion intervertebral movement, and the flexion view (B),

(B) and extenparticularly, ex-

FIG 9. In this horizontal-beam lateral radiograph, the physiologic anterior translation of individual vertebrae is, in the recumbent position, coupled with anomalous hypertrophy of the uncinate processes of C3 (and C4), and creates the illusion of hyperkyphotic angulation at C3-4 and, therefore, anterior subluxation. However, careful analysis of the C3-4 relationship demonstrates that none of the other signs of anterior subluxation is present. Specifically, there is no “fanning,” the contiguous facets are congruous, the inferior facets of C3 completely cover the superior facets of C4, the interval between the posterior cortex of the body of C3 and the superior articular process of C4 is normal, as is the third cervical disc space. Therefore, this patient does not meet the criteria of anterior subluxation.

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FIG 10. Anterior subluxation of C5. In the lateral radiograph (A), a localized hyperkyphotic reversal of cervical lordosis is present at C5-6. The fifth cervical vertebra is both rotated and translated anteriorly. The C5-6 interspinous and interlaminar distances are abnormally wide (“fanning”). The C5-6 apophyseal joints are subluxated anteriorly, resulting in a large area of the superior facet of C6 being uncovered (arrowheads) by the inferior facet of C5 (“naked” facet). The asterisk denotes the abnormally wide distance between the anterior cortex of the superior articular process of C6 and the posterior cortex of the body of C5, and the posterior aspect of the fifth intervertebral space is widened posteriorly and narrowed anteriorly. In the frontal projection (B), the C5-6 interspinous distance (arrow) is abnormally wide, reflecting the “fanning” seen in the lateral radiograph in A. Right (C) and left (0) anterior oblique projections demonstrate subluxation of the articular masses of C5 (arrows). Consequently, the normal “shingles-on-the-roof” alignment of the laminae is distorted as the laminae of C5 (arrowheads) and articular masses are “perched” with respect to those of C6 (stemmed arrows).

cervical spine. The interspinous spaces are of similar width, and the relationships of the articular facets and their contiguous posterior cortical margins are normal and uniform. Flexion and extension views demonstrated only physiologic movement of the vertebral bodies and their posterior elements with respect to each other. Thus, although Curr

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the patient sustained a flexion injury of the cervical spine, and experienced pain, some limitation smooth, &fise, uninof motion, and generalized, terrupted (i.e. physiologic) reversal of the cervical lordosis in the neutral lateral radiograph, none of the criteria of anterior subluxation were present, even when the spine was “stressed” by flexion. 173

FIG 11. Anterior subluxation of C3 with hyperkyphotic angulation limited to the C3-4 level with “fanning,” subluxation, and loss of parallelism of the C4-5 facets and slight, but definite, anterior translation of C3.

Therefore, although this patient may have experienced a soft tissue injury in the cervical region, there is no radiographic evidence of anterior subluxation. The importance of careful analysis of the cervical vertebrae and of strict adherence to the radio-

graphic signs of anterior subluxation is particularly well illustrated in Figure 9 in which congenitally hypertrophied uncinate processes of C3 create the impression of a hyperkyphotic angulation at the C&3 level due to anterior subluxation of CL However, careful analysis of the posterosuperior aspect of the C3 vertebral body (also C4) and recognition that none of the other radiographic signs of anterior subluxation exist exclude the diagnosis. The clinical condition of the patient is extremely important in the evaluation of the radiographs. Patients with acute anterior subluxation typically have severe pain, marked limitation of flexion and extension, and point tenderness over the involved interspinous space(s). An abrupt change in cervical lordosis characterized by localized hyperkyphotic angulation limited to the level(s) of posterior ligament tear* is the cardinal radiographic feature that distinguishes anterior subluxation from the physiologic attitude of the cervical spine in the straight (“military”) or flexed position. The entire spectrum of radiographic signs of anterior subluxation is demonstrated in Figures 10 through 12, from the most obvious (see Fig 10) to the most subtle (see Fig 12). At the level of subluxation, the interspinous and interlaminar spaces are abnormally wide as a result of disruption of the supraspinous and interspinous ligaments. The principal sign of disruption of the posterior ligament complex is the increase in height of the interspinous space referred to as “fanning” by Fielding.18 The vertical height of the interspinous spaces is frequently difficult to evaluate because of the common variation in size and configuration of the spinous processes. In

FIG 12. Anterior subluxation of C3. Focal hyperkyphotic angulation at C3 interspace is subtle, lordotic curve of the posterior cortical margins of C2 and C3 caudally and the same radiograph (A). “Fanning” (arrowheads) is present at this level, and the third vertebra imately 1-2 mm. The findings seen in the neutral lateral projection (A) are accentuated 174

but it can be clearly established by projecting the curve from C4 to Tl rostrally in the neutral lateral is anteriorly translated with respect to C4, approxin flexion (B) and reduced in extension (C). Cum

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contrast, the laminae are more constant in shape and vertical height and, consequently, the interlaminar distance is normally more constant than the interspinous distance. Abnormal widening of the interlaminar space is, therefore, a more reliable sign of “fanning” than is widening of the interspinous space although, obviously, those spaces are continuous and are both widened in “fanning” (see Figs 10-12). As the involved vertebra rotates and translates anteriorly, its articular masses are distracted from those of the subjacent vertebra. Consequently, the inferior facet of the subluxated vertebra may no longer be parallel to the superior facet of the subjacent vertebra nor cover it completely, thus producing the partially “exposed” or “naked” facet. The magnitude of these important signs of anterior subluxation is directly proportional to the magnitude (or severity) of the subluxation. The intervertebral disc space subjacent to the subluxated vertebra becomes widened posteriorly and narrowed anteriorly as a result of forward rotation of the involved vertebral body. The involved vertebra (see Figs 10 through 12) may or may not be anteriorly displaced (translated) with respect to

the subjacent vertebra. When subtle in the neutral lateral radiograph (see Figs 10 and ll), the signs of anterior subluxation are accentuated in flexion (see Fig 12). Magnetic resonance imaging (MRI) provides a means for resolving one of the perplexing clinical and radiologic ambiguities related to the diagnosis of acute anterior subluxation. Because anterior subluxation was frequently unrecognized and consequently inadequately treated in the past and because of its high incidence of impaired or failed ligamentous healing (“delayed instability”), it is not uncommon that a patient sustains an acute “whiplash” injury to the neck, complains of only diffuse mild to moderate neck pain, and has radiographic signs of anterior subluxation. The patient may or may not recall having sustained previous cervical spine trauma, which could have resulted in prior anterior subluxation with delayed instability. The diagnostic problem is the acuteness of the soft tissue changes reflected by the plain-film signs of anterior subluxation. Resolution of this dilemma is critical to subsequent management since many advocate posterior fusion as the most conservative treatment of acute disruption of the posterior liga-

FIG 13. Anterior subluxation of C4 with all classic signs demonstrated on the lateral radiograph, A. The GRASS (TR 1000, TE 25) sequence image, 0, demonstrates “fanning” of the interspinal space (asterisk), disruption of the posterior longitudinal ligament and annulus at C5-6 (arrowhead) with the high intensity signal of blood and/or edema extending rostrally posterior to C5 and C4 (arrows), as well as the anterior rotation and slight anterior translation of the entire fifth vertebra. C, the TPweighted (TR 2000, TE 70) image, demonstrates the high-intensity signal of acute posterior ligamentous injury (asterisk) and minor anteroposterior compression of the cord posterior to the fifth disc. The GRASS (TR 1000, TE 25) second echo image, D, demonstrates focal edema of the spinal cord (arrowhead) at this level.

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ment complex. Conversely, if the injury is old and was asymptomatic prior to the acute trauma, no treatment may be indicated. Magnetic resonance images depict the typical plain-film signs of anterior subluxation. More importantly, magnetic resonance demonstrates and confirms the soft tissue pathology of anterior subluxation only indirectly seen on the plain neutral lateral cervical radiograph, such as the high-intensity signal of edema in the acutely torn posterior ligament complex, separation of the posterior longitudinal ligament from the subluxated vertebra, disruption of the posterior annulus of the involved disk and, when present, blood at the site of the annular and disk tear. These injuries might intu-

itively be expected to occur in anterior subluxation, but have not been previously described or illustrated. The high intensity signal of blood and/or edema in the widened interlaminar and interspinous space (Figs 13 and 14) is indicative of an acute injury. The absence of this magnetic resonance finding in a patient with plain-film signs of anterior subluxation indicates that the injury is old (Fig 15). Anterior subluxation usually occurs at a single level but, depending on the magnitude and direction of the causative force, may involve more than one cervical segment (Fig 16). In the recumbent patient, anterior subluxation may be even more difficult to identify than usual

FIG 14. A, lateral radiograph demonstrating subluxation of C2 and cervicocranial prevertebral soft tissue swelling associated with a clay-shoveler’s type fracture of its spinous process (arrow). Disruption of the posterior annulus of the C2 disc (arrowhead) and separation of the posterior longitudinal ligament (curved arrow) from the posterior cortex of the axis vertebra by blood or edema (arrow) are demonstrated on the T, weighted (TR 800, TE 20) image (8). The first echo GRASS image (C), confirms the soft tissue injuries seen in B and, in addition, demonstrates a high intensity signal (asterisk) in the C2-3 interspinous space reflecting edema and/or blood and an acute injury. The second echo GRASS image (D), reveals the dark signal of blood in both the interspinous space and the posterior aspect of the second intervertebral disc (arrows). 176

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FIG 15. Subtle signs suggesting anterior subluxation of C4, present in the neutral lateral radiograph (A), prompted a lateral flexion view(B), which confirms disruption of the posterior ligament complex. The T,-weighted (TR 800, TE 20) (C) and the first and second echo T,-weighted (TR 2000, TE 80) images (D and E, respectively) are all negative. The absence of magnetic resonance signs of edema or hemorrhage or of ligamentous disruption indicates that the anterior subluxation is not acute.

and may be heralded primarily by a widened interspinous distance (“fanning”) (Fig 17). If the supine lateral radiograph is equivocal, a lateral examination made in flexion-even recumbent if dictated by the clinical circumstances-should establish (Fig 18) or exclude the diagnosis. When anterior subluxation occurs in a patient with preexistent degenerative arthritis, the subluxation usually occurs in that portion of the cervical spine not involved by the degenerative process (Fig 19). All of the roentgen signs of anterior subluxation are accentuated in flexion and diminished in extension (see Figs 12, 16, and 18). Widening of the interspinous distance in the anteroposterior radiograph of the lower cervical spine is an important sign of a flexion injury, inCurr

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eluding anterior subluxation. The increased interspinous distance on the anteroposterior radiograph (Fig 20) confirms subtle “fanning” on the lateral radiograph or may indicate posterior ligamentous tear when, on the lateral radiograph of the cervical spine, the involved segments are obscured by the density of the shoulders (Fig 21). The radiographic signs of delayed or failed ligamentous healing, (delayed instability) are seen in Figure 22. The morbidity of delayed instability is sufficient to warrant repeated emphasis: (1) delayed instability is commonly a complication of “minor” acute cervical spine injuries, i.e., anterior subluxation or “simple” wedge fracture, and (2) the incidence of delayed instability following subluxation ranges from 21% to 50%? 177

FIG 16. Anterior subluxation at multiple levels. The neutral radiograph, (A), demonstrates diffuse reversal of cervical lordosis, presumably due to muscle spasm since the mandible is not in the “military” attitude with respect to the cervical spine. “Fanning” is present at both the C4-5 and G-6 levels; the interfacetal joint surfaces are not congruous and the superior facets of C6 are only partially covered; the fourth disc space is widened posteriorly and narrowed anteriorly and C4 is anteriorly translated approximately 2-3 mm. The fifth disc space is normal and C5 IS translated only 1 mm anteriorly. All these signs are accentuated in flexion (6) and reversed in extension (C).

FIG 17. In this supine lateral radiograph, anterior subluxation is indicated by “fanning” at the C4-5 interlaminar and interspinous spaces (arrow) and also by changes in the positional relationships of the facets of the involved apophyseal joints described in the text.

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FIG 18. A, ini itial supine lateral radiograph of the cervical the occiput establishes ing fc9ded sheets beneath

spine equivocal the presence

subluxation. Supine flexion radiograph, for anterior (arrow) and, therefore, anterior of (Z3-4 “fanning”

B, obtained subluxation.

by plac-

FIG 19. Ante :rior subluxation

of C4 rostra1

to severe

degenerative

arthrosis.

FIG 20. Widening of the interspinous reflects “fanning.”

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distance

(arrows)

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FIG 21. Increased interspinous distance (arrow) in the frontal radiograph, A, was the only indication of anterior subluxation tion of this patient in whom the shoulders obscured the lower cervical segments in the lateral projection (B). The tained during upper extremity traction (C) confirmed anterior subluxation of C5.

Although anterior subluxation is a specific injury, disruption of the posterior ligament complex is an integral component of other cervical injuries in which flexion is a major vector force in the mechanism of injury. When associated with the “simple” wedge fracture (Fig 23) failure of the posterior ligament complex tear to heal results in delayed instability and may become of greater clinical significance than the fracture itself, which invariably heals .I Disruption of the posterior liga-

in the initial examinalateral radiograph ob-

ment complex is an integral component of total ligamentous disruption characteristic of both bilateral interfacetal dislocation and the flexion teardrop fracture. The posterior ligament complex is also disrupted in unilateral interfacetal dislocation, which is the result of simultaneous flexion and rotation. Conversely, the intact posterior ligament complex is the basis for the avulsion fracture of a cervicothoracic spinous process--“clay shoveler’s” fracture-also a flexion injury.

FIG 22. A, anterior subluxation of C3-4 on the initial lateral rigid immobilization with asterisk indicating grossly 160

radiograph. widened

B, “delayed instability” interspinous space.

of failed

ligamentous

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FIG 23. Simple fracture motion

HYPEREXTENSION

wedge fracture of (2.5 in initial lateral radiograph (A). Eleven months post-trauma, the had healed, but failure of the posterior ligament complex to heal resulted in abnormal during flexion (B) and extension at C5-6 (C), i.e., “delayed instability.”

DISLOCATION

The term hyperextension dislocation is a paradox, since a fundamental condition of the diagnosis is that the cervical vertebrae be normally aligned. Indeed, this injury has been described as the “syndrome of the paralyzed patient with norrefers to malappearing spine. “1s--21 “Dislocation” the posterior displacement of a vertebra and those rostral to it, with respect to its subjacent segment at the time of a posterior force delivered to the face. The absence of dislocation on the initial, and subsequent, lateral radiograph(s) of the cervical spine is the basis for the reluctance of the radiologic community to acknowledge the injury and the term “hyperextension dislocation.” In recent literature, some authors have referred to the hyperextension dislocation in terms that vary from the original pathologic description, e.g., “hyperextension sprain (momentary dislocation) with fracture”‘” and “hyperextension sprain.“z3 However, based upon autopsy findings, animal experiments,24-26 and in keeping with the generally accepted clinical usage, the traditional term “hyperextension dislocation of the cervical spine” should be reserved specifically for this injury though even, by definition, the dislocation is not radiographitally present on post-trauma lateral radiographs of the cervical spine. GENERAL

Hyperextension dislocation acute cervical spine injury Curr

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“family” of injuries caused by a predominantly hyperextension mechanism of injury (Table 21. Hyperextension dislocation is frequently not recognized radiographically because the vertebrae are uniformly normally aligned; there is no dislocation. Hence, the significance of the characteristic avulsion fracture fragment present in approximately two thirds of the patients with hyperextension dislocation is frequently not appreciated. The diagnosis of hyperextension dislocation is usually established by the presence of an acute central cervical spinal cord syndrome in a patient who has sustained facial or craniofacial trauma and in whom the lateral cervical radiograph reveals normally aligned cervical vertebrae and diffuse prevertebral soft tissue swelling.“’ 27-2s MECZWNISM

OF

INJURY

Although any circumstance that delivers a posteriorly directed major force to the face may cause TABLE Injuries

2. Caused

by a Hyperextension

Mechanism*

Hyperextension Hyperextension dislocation Avulsion fracture of anterior arch of atlas Extension teardrop fracture of axis Fracture of posterior arch of atlas Laminar fracture Traumatic spondylolisthesis (hangman’s fracture) Hyperextension fracture-dislocation *From Harris JH Jr, Ed&en-Monroe Orfhop C/in North Am 1986; 17:15-30.

B, and

Kopaniky

DB:

Used by permission. 181

the dislocation, hyperextension dislocation of the cervical spine is usually the result of a high velocity, abrupt deceleration, motor vehicle accident. The true incidence of hyperextension dislocation is not known, in part at least, because the radiographic signs have not been generally recognized or appreciated. PATHOPHYSIOLOGY Hyperextension dislocation of the cervical spine was first defined pathologically by Taylor and Blackwoodzg in 1948. Their patient suffered an acute injury of the cervical spine “in which damage to the cervical part of the spinal cord appears without radiographic evidence of vertebral injury or displacement.” Autopsy of this patient revealed that the anterior longitudinai ligament was ruptured between the sixth and seventh cervical vertebrae, the column had been torn through by detachment of the intervertebral disc from the lower surface of the sixth vertebral body. The upper segment of the column, carrying with it the intact posterior longitudinal ligament, could be displaced backward on the lower segment with great ease, the disc remaining attached to the upper surface of the seventh vertebra and the posterior longitudinal ligament being lifted from its posterior surface. In discussing this patient, Taylor and Blackwood stated, “A backward thrust applied through the head does cause dorsal dislocation or fracture at the lower levels of the cervical spine” and that injury causing the syndrome of a paraplegic patient with normally aligned, intact cervical vertebrae is “extension dislocation with immediate spontaneous reduction.” The identical combination of clincal, radiographic, and autopsy findings was described in four additional patients included in a study of 45 patients with hyperextension injury of the cervical spine reported by Mara? in 1974. As part of his study, Marar demonstrated that the application of a “backward rotation” force with simultaneous “strong posterior displacement (shearing) force” on the head and neck of cadavers produces “definite backward subluxation.” Of six patients over 60 years of age reported by Borovich et al.,3o one developed acute central cervical spinal cord syndrome subsequent to a fall. The lateral cervical radiograph was negative for fracture or dislocation. The patient died, and autopsy revealed that the anterior longitudinal ligament was torn, the disc was disrupted horizontally, and the posterior longitudinal ligament was avulsed from the posterior aspect of the subsequent vertebra, i.e., hyperextension dislocation. 182

The pathologic lesion of hyperextension dislocation seen at autopsy by Taylor,31 Marar,l’ and Borovich et aL3’ has been produced in anesthetized monkeys in studies by MacNab,24 Cintron et al .,32 and Gosch et aLz6 Even prior to the cadaver and animal research just cited, earlier authors had postulated just such an injury. Extension (hyperextension) dislocation of the cervical spine was first described by Wilson and Cochran in 1920.33 In 1941, Mixter34 hypothesized such a case by stating that “posterior dislocation is rare on account of the strong supporting structures, and, if it does occur, I believe that

spontaneous

reduction

might easily take place.”

Post-traumatic tetraplegia without cervical fracture or dislocation was explained by Courville35 and Watson-Jones36 using the “recoil theory,” defined as “momentary extreme vertebral dislocation causing cord damage with immediate spontaneous reduction of the dislocation.” Pancoast and Pendergrass37 defined the recoil theory as “sudden massive dislocation of a vertebral body, which then reduces itself by antagonistic muscle action.” Forsyth” referred to this injury as hyperextension dislocation, while Gehweiler et al.” referred to it as “hyperextension sprain (momentary dislocation) with fracture” and Braakman and Penning as “hyperextension sprain.” The pathology of hyperextension dislocation described by Taylor and Blackwoodzs and subsequently by Marar” has been produced in anesthetized monkeys.24-26 The pathologic lesion of hyperextension dislocation consists of rupture of the anterior longitudinal ligament and either avulsion of the involved vertebra from the subjacent disc or horizontal rupture of the disc. Continued posterior excursion of the involved vertebra strips the posterior longitudinal ligament from the subjacent vertebral body, allowing the dislocating vertebra to impinge upon the ventral surface of the spinal cord. Simultaneously, kyphotic angulation occurs posteriorly at the level of dislocation, causing the ligamentum flavum and dura to impinge upon the posterior aspect of the cord. Magnetic resonance images provide in vivo confirmation of the pathologic changes of hyperextension dislocation described at autopsy and produced experimentally in animals and cadaver specimens. The pathology demonstrated by magnetic resonance also provides the basis of the soft tissue signs seen on the lateral cervical spine radiograph. The pathologic changes due to hyperextension dislocation so clearly demonstrated by MRI include disruption of the anterior longitudinal ligament, disruption and increase in the vertical height of the intervertebral disc, hemorrhage Cum

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into the disc space, as well as separation of the posterior longitudinal ligament from the posterior aspect of the subjacent vertebra and, when present, rostrally. Narrowing of the anteryoposterior diameter of the spinal canal between the posteriorly translated vertebral body and the posterior laminar line of the subjacent vertebra, which is the basis for cord compression and the acute central cervical cord syndrome, is clearly demonstrated. The etiology of the diffuse prevertebral soft tissue swelling, which is the principal plain-film sign of hyperextension dislocation, is explained by the high intensity magnetic resonance signal, which represents blood and edema in the prevertebral (retropharyngeal) fascial space.3s In addition, MRI uniquely, and for the first time, accurately depicts the location, the extent, and even the histopathology of the spinal cord injury associated with hyperextension dislocation in vivo. Edema, hemorrhage, or a combination of the two, correlate with their magnetic resonance images and the clinical outcomes of patients with acute spinal cord injuries.40-42 More recently, this correlation has been established by relating the histopathology and the magnetic resonance images of experimentally induced spinal cord injuries in a rat mode1.43 In the past, metrizamide computed tomography was the best way to demonstrate epidural hemorrhage and cord swelling associated with hyperextension dislocation. That same information is more accurately and clearly recorded in both sagittal and axial planes by magnetic resonance without the introduction of intrathecal contrast and without the patient discomfort and inconvenience associated with cervical myelography. The unique contribution of magnetic resonance to the radiologic evaluation of hyperextension dislocation is, as previously described, the accurate in vivo identification and delineation of the extent of spinal cord injury, and magnetic resonance signal characteristics that have a direct correlation with the cord histopathology. The spectrum of MRI features of hyperextension dislocation is illustrated in Figures 24 through 27. Anteroposterior compression of the spinal cord (Fig 28) results in the acute central cervical spinal cord syndrome characterized by sensory changes below the level of dislocation and motor impairment that is greater in the upper extremities than in the lower extremities. Bladder dysfunction, resulting in urinary retention, may be present. Depending on the type and degree of central cord damage, tetraplegia may be transient, permanent, or cause death.27J 3o There may be little correlation between the radiologic and neurologic findings.38 Cur-r

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FIG 24. All the classically described soft tissue changes of hyperextension dislocation are clearly documented in the sagittal T, weighted (TR 2000, TE 30) image. From anterior to posterior, these include blood and/or edema in the retropharyngeal space producing prevertebral soft tissue swelling (asterisk), disruption of the anterior longitudinal ligament and annulus (arrow), increase in vertical height of the disc, blood in the disc (arrowhead), disruption of the annulus posteriorly (curved arrow) and stripping of the posterior longitudinal ligament (open arrow) from the posterior cortex of the subjacent vertebra, and narrowing of the anteroposterior diameter of the spinal canal with cord compression between the “dislocated” vertebral body and the lamina of the subjacent vertebra.

The extent of neurologic recovery is related to the extent and nature of the cord damage.“’ 27, 3o RADIOGJ3APHZC DIAGNOSIS The radiographic signs of hyperextension dislocation have been described as diverse44-46 and subtle.lg’ “, 47 Many authors have described various radiographic signs of hyperextension “inju49 ~~~~~~~~ untfi the recent ries. r14-16,22,29,32,45.48> article by Edeiken-Monroe et al.,5o there had not been a comprehensive description of the radiographic signs of the specific injury, hyperextension dislocation. Rupture of the anterior longitudinal ligament, which may occur with a force of as little as 340 psi,5l is manifested radiographically by diffuse widening of the prevertebral soft tissues and blurring of the air-soft tissue interface secondary to hemorrhage and edema associated with the ligamentous tear (Fig 291.45 Weir4’ established the normal width of the prevertebral soft tissues at the level of the anterior inferior border of C3 in adults to be 2.6 to 4.8 mm with a target-film distance of 6 feet (2.0 ml. Therefore, prevertebral soft tissue shadow exceeding 5 mm at this level is abnormal. The shortest target-film distance used in obtaining lateral cervical spine radiographs at our institution is 40 inches (1.0 m), which results in a maximum magnification factor of 1.4 and a normal adult prevertebral thickness of 7 mm as measured 183

FIG 25. Hyperextension dislocation of C3 characterized by normally aligned and intact cervical vertebrae, widening of the third disc space and diffuse prevertebral soft tissue swelling on the lateral radiograph (A). The sagittal GRASS (TR 1000, TE 9) cardiac-gaited first echo image (B) and the spin-echo T, weighted (TR 2400, TE 70) image (C) demonstrate the high intensity signal (asterisk) of edema and/or hemorrhage in the prevertebral space, disruption of the anterior longitudinal ligament and annulus (arrow) at the third disc, increased vertical height of the third disc, and high intensity signal of blood in the anterior part of the disc, (arrowhead). The GRASS (TR 1000, TE 25) second echo axial image (D) shows the high intensity signal of edema and/or hemorrhage (asterisk) in the retropharyngeal space anterior to the vertebral body and to the longus colli and longus capitis muscles (arrows), which causes the diffuse prevertebral soft tissue swelling seen on the lateral radiograph (A). The GRASS (TR 1000, TE 25) second echo sagittal image (E) demonstrates, in addition to the soft tissue abnormalities recorded in B and C, anteroposterior narrowing of the cord at the C3 level with separation of the posterior longitudinal ligament from the posterior cortex of the body of C3 (arrow). The GRASS (TR 1000, TE IO) first echo axial image F obtained through the midplane of the body of C3 confirms separation of the posterior longitudinal ligament (arrowheads) from the posterior cortex by blood and/or edema.

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FIG 26. The initial supine lateral radiograph of the cervical spine (A) is normal. A subsequent lateral radiograph obtained in hyperextension 1 (B) tonstrates slight widening of the fifth disc space anteriorly and prevertebral soft tissue swelling at this level. The T,-weighted (TR 800, TE 5!O) sagittal image (C) is normal, but the cardiac-gaited T2 (TR 3000, TE 70) sagittal image (D) demonstrates a high intensity sigr lal of na in the spinal cord (arrows).

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FIG 27. The sixth intervertebral disc space is slightly, but definitely, widened anteriorly, and localized prevertebral soft tissue swelling is present at this level in the lateral radiograph (A) of a patient with hyperextension dislocation. The T,-weighted (TR 800, TE 20) sagittal image (B) confirms the localized prevertebral soft tissue swelling and increased height of the disc space and demonstrates disruption of the annulus and the anterior longitudinal ligament as well as posterior bulging of the disc with displacement of the posterior annulus and the posterior longitudinal ligament (arrowhead). All of these findings are confirmed in the cardiac-gaited GRASS (TR 1000, TE 9) sagittal image (C).

Posterior ,longitudinal Anterior

Avulsion Sharpey’s

fragmen fibers

Spinal cord

ilbs

FIG 28. Schematic representation of the pathophysiology of hyperextension dislocation. This illustration depicts the characteristic fracture fragment avulsed by the intact Sharpey’s fibers and both anterior and posterior compression of the spinal cord, which results in the central cord syndrome. 186

at C3. The prevertebral soft tissue shadow at this disloca1level in all patients with hyperextension tion reported by Edeiken-Monroe et a.L5' ranged from 9 to 19 mm. Furthermore, in a majority of these patients, the width of the prevertebral soft tissue was more than double the 7 mm upper limit of normal. In all patients with hyperextension dislocation, except adolescents, the prevertebral soft tissue swelling is diffuse and involves the entire cervical region, extending even to the nasopharynx and the clivus. In adolescents in whom the ununited ring apophysis is avulsed (Fig 301, the soft tissue swelling is localized. Avulsion of the apophysis, limited soft tissue swelling, and minimal neurologic findings all suggest that these injuries were less severe than those occurring in adults who have diffuse 1prevertebral soft tissue swelling. The avulsion fracture fragment of hyperextension dislocation is characteristic of this injury” and occurs in two thirds of the patients with hydislocation. The separate fragment, 1perextension which is avulsed by the intact Sharpey’s fibers of the annulus,52J 53 arises from the anterior aspect of the inferior end-plate of the involved vertebra. Typically, the horizontal dimension of the fragment is greater than its vertical height (Fig 31). Curr

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FIG 30. Lateral cervical spine radiograph of an adolescent with hype rextension dislocation. The arrow points to the avulsed ring apof ,hysis. Prevertebral soft tissue swelling is localized and confinec 3 to the area of the avulsion.

FIG 29. Horizontal-beam bra1 soft tissue bra in a patient

lateral radiograph demonstrating diffuse preverteswelling and intact, normally aligned cervical vertewith clinical signs of a central cord syndrome.

The fracture fragment caused by hyperextension dislocation must be distinguished from that of the extension teardrop fracture because of the significant clinical difference between these two injuries. The avulsion fracture of hyperextension dislocation (Fig 32,A) is characterized by its location and by the fact that its horizontal dimension is greater than its vertical height. Conversely, the vertical height of the extension teardrop fragment (Fig 32,B) equals or exceeds its horizontal dimension. Appreciation of the distinctive characteristic features of the separate fragment of hyperextension dislocation and extension teardrop fracture is of added ‘importance since both hyperextension and extension teardrop fractures commonly involve the axis vertebra. Widening of the intervertebral disc space (Fig 33) may become radiographically evident only when Curr

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FIG 31. Typical avulsion fracture of hyperextensron horizontal dimension exceeds its vertical

dislocation height.

(arrow).

The

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FIG 32. fracture of hyperextension dislocation (A) and the extension inferior aspect of the axis body, hyperextension dislocation fracture fragment as well as diffuse prevertebral soft tissue height of the separate fragment being equal to or exceeding

teardrop fracture (B). Although each of these fractures involves the is characterized by the typical location and the configuration of the swelling. The extension teardrop fracture (B) is characterized by the its transverse dimension and the relatively less soft tissue swelling.

the cervical spine is examined in extension. Cintron et a13’ emphasized that a widened disc space may indicate ‘a potentially unstable lesion.” The vacuum defect is a horizontal, oval lucency within the intervertebral disc space (Fig 34). This “lucent cleft” was first reported as a sign of cervical

disc injury or disease by Reymond et al.,48 who postulated that the lucency represented gas (probably nitrogen) diffused into the joint space by the negative pressure associated with avulsion of the inferior end-plate of the affected vertebra from the subjacent disc. A vacuum disc occurred in approximately one third of patients with hyperextension dislocation.50 When present, the vacuum disc of hyperextension dislocation has been located in the midplane of the disc space. Spinous process fractures resulting from hyperextension are secondary to compression of the involved spinous process between adjacent processes. The radiographic characteristics of the spinous process fracture associated with hyperextension dislocation ditfer from those of the clayshoveler’s fracture.

Avulsion anterior avulsion vertical

DIFFERENTLM

FIG 33. Hyperextension dislocation of C4 characterized by increase in vertical height of the fourth intervertebral disc space (open arrow) and diffuse prevertebral soft tissue swelling.

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DLAGNOSIS

Hyperextension dislocation is pathologically and radiographically distinct from the spinal cord compression injury that occurs in extension and is associated with cervical spondylosis, as described by Taylor3’ and Borovich et aL3’ i.e., the “Taylor mechanism.” In the latter type, in which the lateral cervical spine radiographs were all negative except for the presence of osteophytosis, the central cord syndrome was best explained by pinching of the cord by the osteophytes anteriorly and by the inbulging dura and ligamentum flavum posteriorly. At autopsy, Taylor3* reported that the spinal colCurr

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REFERENCES Green JD, Harle TS, Harris JH Jr: Anterior subluxation of the cervical spine. AJNR 1981; 2843. 2. McGahan JP, Benson D, et al: Intraoperative sonographic monitoring of reduction spinal fractures (abstract). Presented at Radiological Society of North America Scientific Assembly, Washington DC, 1984. celvical subluxation: An unstable 3. Scher AT: Anterior position. AJR 1979; 133275. sprain of the 4. Braakman R, Penning L: The hyperfIexion cervical spine. Radio1 Clin Biol 1968; 37:309. 5. Selecki BR, Williams HBL: Injuries to the Cervical Spine and Cord in Man. Menyn Archdall Medical Monograph Number 7, New South Wales, Australian Medical Publishing Co, 1970. 6. Cramer F, McGowan FJ: The role of the nucleus pulposus in the pathogenesis of so-called “recoil” injuries of the spinal cord. Surg Gynecol Obstet 1944; 79:516. 7. Jackson R: Up-dating the neck. Trauma 1970; 1:s. of the cervical 8. Rogers WA: Fractures and dislocations spine. J Bone Joint Surg lAmI 1974; 56:1675. 9. Taylor RG, Gleave JRW: Injuries to the cervical spine. Proc R Sot Med 1962; 55:1053. lesions of the cetical spine: Sta10. Stringa G: Traumatic tistics, mechanism, classification, in Proceedings of the Ninth Congress of the International Society of Othopaedic Surgeons and Traumatology. Brussels, Imprimerie des Sciences, 1963, pp 69-97. F: Fractures, dislocations and fracture: dis11. Holdsworth locations of the spine. J Bone Joint Surg 1970; 52A:1534. 1.2. Cheshire DJ: The stability of the cervical spine following the conservative treatment of fractures and fracture-dislocations. Paraplegia 1969; 7:193. of cervical 13. Whitley JE, Forsyth HF: The classification spine injuries. AJR 1960; 83:633. 14. Harris JH Jr: The Radiology of Acute Cervical Spine Trauma, ed 2. Baltimore, Williams &Wilkins, 1986. 15. Scher AT: Diversity of radiologic features in hyperextension injury of the cervical spine. S Afr Med J 1980; 58:27. 16. Harris JH Jr, Harris WH: The Radiology of Emergency Medicine, ed 2. Baltimore, Williams & Wilkins, 1981. of the 17. White AA III, Panjabi MM: Clinical Biomechanics Spine. Philadephia, JB Lippincott, 1978. 18. Fielding JW, Hawkins RJ: Roentgen diagnosis of the injured neck. AAOS lnstr Course Lect 1976; 25:149. injuries of the cervical spine: 19. Marar BC: Hyperextension The pathogenesis of damage to the spinal cord. J Bone Joint Surg [AmI 1974; 56:1665. HF: Extension injuries of the cervical spine. J 20. Forsyth Bone Joint Surg lAmI 1964; 46:1792. JA Jr, Miller MD, et al: Lateral hy21. Schaaf RE, Gehweiler perflexion injuries of the spine. Skeletal Radio1 1978; 3:73. JA Jr, Clark WM, Schaaf RE, et al: Cervical 22. Gehweiler spine trauma: Common combined conditions. Radiology 1979; 130:77. 23 Braakman R, Penning L: Injuries of the Cervical Spine. Amsterdam, Excerpta Medica, 1971. 24. MacNab I: Acceleration injuries of the cervical spine. J Bone Joint Surg lAmI 1964; 46:1797. 25. Harris W, Hamblen D, Ojemann R: Traumatic disruption of cervical intenrertebral disc from hyperextension injury. C/in Orthop 1968; 60:163. 26. Gosch HH, Gooding E, Schneider R: An experimental study of cervical spine and cord injuries. J Trauma 1972; 12:570. 1.

FIG 34. A and B, hyperextension dislocation of C4 characterized by normally aligned and intact cervical vertebrae, a “vacuum” defect in the center of the fourth intervertebral disc space (arrowhead) and diffuse prevertebral soft tissue swelling.

umn, including the anterior longitudinal ligament, was intact. Myelographic cadaver experiments demonstrated that, in hyperextension, a series of posterior indentations at the level of the interlaminar spaces narrowed the canal by as much as 30%, secondary to infolding of the ligamentum flavum differs from and dura.31 The Taylor mechanism hyperextension dislocation because of the absence of any radiographic abnormality of the cervical spine except the degenerative disease. Specifically, in the Taylor mechanism, the cervical prevertebral soft tissues are normal. ACKNOWLEDGMENT The authors acknowledge, with gratitude and appreciation, the exemplary photographic work of Susan Van Velzer, B.S. Without the secretarial support and assistance and the untiring efforts of Kathy Norred, this work would not have been completed. Curr

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spinal cord injury: A study using physical examination and magnetic resonance imaging. Spine 1988, in press. Mirvis SE, Geisler FH, Jelinek JJ, et al: Acute cervical spine trauma: Evaluation with 1.5 T MR imaging. Radiology 1988; 166:807-816. Weirich SD, Cotler HB, Narayana PA, et al: Histopathologic correlation of magnetic resonance image signal patterns in a spinal cord injury model. Presented at the 35th annual meeting of the Orthopaedic Research Society, Las Vegas, Nevada, Feb 6-9, 1989. Clark WH, Gehweiler JA, Laib R: Twelve significant signs of cervical spine trauma. Skel Radio1 1979; 3:201. Penning L: Prevertebral hematoma in cervical spine injury: Incidence and etiologic significance. AJNR 1981; 1:557; AJR 1981; 136653. Schneider RC, Cherry G, Pantek H: The syndrome of acute central cervical spinal cord injury. J Neurosurg 1954; 11:546. Scher A: Hyperextension trauma in the elderly: An easily overlooked spinal trauma. J Trauma 1983; 23:1066. Reymond RD, Wheeler RS, Parovic M, et al: The lucent cleft, a new radiologic sign of cervical disc injury or disease. C/in Radio1 1972; 23:188. Weir DC: Roentgenographic signs of cervical injury. Clin Orthop 1975; 109:9. Edeiken-Monroe B, Wagner LK, Harris JH Jr: Hyperextension dislocation of the cervical spine. AJNR 1986; 7:135. Davis A: New aspects of spinal injury. Arch Surg 1943; 46:619. Keller RN: Traumatic displacement of the cartilagenous vertebral rim: A sign of intervertebral disc prolapse. Radiology 1974; 110:21. Osteology, in Goss CM ted): Gray’s Anatomy of the Human Body, ed 29. Philadelphia, Lea & Febiger, 1973, p 320.

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