Cervical spine trauma in children: Part I. General concepts, normal anatomy, radiographic evaluation

Reviews

Cervical Spine Trauma in Children: Part I. General Concepts, Normal Anatomy, Radiographic ivaluation WILLIAM A. BONADIO, MD It is frequently the responsibility of emergency physicians to perform the initial assessment of trauma victims and evaluate for possible cervical spine injury (CSI). In these cases, defining the anatomic and functional status of the cervical spine takes precedent after performing any necessary resuscitative measures. It requires a skill based on both knowledge and experience to accurately and expeditiously evaluate for possible cervical spine injury while ensuring controlled spinal alignment in a neutral position. The consequences of an unrecognized CSI can obviously be disastrous. It has been shown that as many as 60% of all cervical spinal cord lesions are initially incomplete postinjury, and that 5% to 10% of lesions occur after the traumatic event during the early phases of emergency care.‘-4 In a series of 300 multiple trauma victims with CSI, 11 victims had an initially unrecognized lesion and experienced neurologic deficit or death as a result of inadequate neck immobilization during the course of emergency management.’ In order to maximize the outcome of trauma victims with CSI it is incumbent on the managing physician to have a thorough understanding of the anatomy and biomechanics of the normal cervical spine and of the pathologic manifestations of CSI that can result from a myriad of traumatic events. This two-part article will review anatomic and biomechanical aspects of the cervical spine, describe common pediatric CSIs, demonstrate associated mechanisms and radiographic manifestations of CSIs, and propose guidelines for the initial clinical assessment and management of trauma victims evaluated for possible CSI. DEMOGRAPHICS The National Spinal Cord Injury Data Research Center has estimated that each year in the United States approximately 15,000 to 20,000 individuals sustain traumatic spinal cord injury, with about 70% of lesions involving the cervical spine.’ Approximately 65% of CSIs are associated with mul-

From The Medical College of Wisconsin, Children’s Hospital of Wisconsin, Milwaukee, WI. Manuscript received July 2, 1992; revision accepted October 15, 1992. Address reprint requests to Dr Bonadio, 1240 Pioneer Trail, Waukesha, WI 53188. Kev Words: Cervical spine, trauma, parapleoia, fracture. Copyright 0 1993 by W.B. Saunders Company 07358757/93/l 102-0014$5.00/O 158

tiple trauma: in children and adolescents, motor vehicle accidents are most common (50% of cases), followed by sports-related accidents (20% to 25% of cases) and falls from a significant height (10% to 20% of cases); in the inner city, penetrating trauma accounts for a significant percentage of cases of CSI.‘*4*5 Cervical spine injuries occur in approximately 5% of all victims of multiple trauma, in one of every 300 victims of severe motor vehicle accidents (15% riding motorcycles), and in one of every 14 occupants ejected from a motor vehicle.4,6*7 A pp r oximately 60% of pediatric CSIs are associated with a significant head injury.5 Traumatic spinal cord injuries are most common in males aged 20 to 34 years. Cervical spine injuries are relatively uncommon in children; overall, only about 10% of all such injuries are suffered by those younger than 16 years.‘*’ At one institution fractures and dislocations of the spine in children accounted for only 0.2% of all pediatric fractures and dislocations and only 3% of all spinal injuries encountered.” Combining the results of two large series of over 7,000 traumatized children who received radiographic evaluation of the cervical spine shows that only 1% had an identified lesion.5s’1 The age distribution of children with CSI is younger than 8 years in 10% to 15% of cases, 8 to 12 years in 20% to 25% of cases, and older than 12 years in 60% to 70% of cases.s’1* NORMAL ANATOMY A thorough knowledge of cervical spine anatomy is the foundation on which is built a conceptualization of mechanisms and manifestations of traumatic CSI. A basic knowledge of developmental anatomy is also important and is extensively reviewed elsewhere.‘* The components of the spinal column complex function to support and protect neural elements while allowing a specific physiologic range of motion. The major anatomic components of the cervical spine are the osseous structures, ligaments, intervertebral discs, inter-facet joints, neck musculature, and neural and vascular structures of the neck. Osseous Structures The major osseous structures of the cervical spine are the base of the occipital skull and the first eight vertebrae (Cl to Tl) of the spinal column. With the exception of Cl (atlas), each cervical vertebra is composed

these bony structures

are connected

of a body and an arch;

to form a ring configu-

WILLIAM A. BONADIO n CERVICAL SPINE TRAUMA IN CHILDREN

ration, which defines the boundaries of the spinal canal and contains the spinal cord and subarachnoid space (Figure 1). The vertebral body is elliptically shaped, with central cancellous bone aligned in vertical lamellae (thus giving a lightweight structure that tends to resist direct compression forces) encased by dense compact cortical bone. The C3 vertebra can resist compression forces of up to 300 lbs12; vertebral bodies increase in A-P diameter and compressionresisting strength caudally. The bilateral uncinate processes and transverse processes, which resist forces of lateral displacement, protrude dorsolaterally from the body. The arch is composed of paired pedicles, facets, laminae, and spinous processes. Facets, which provide articulating surfaces between vertebrae, arise from the superior and the inferior surfaces of each lateral arch and are connected anteriorly to the body by pedicles and posteriorly to the spinous processes by laminae. Figure 2 is a lateral view diagram of the osseous articulation of adjacent cervical vertebrae. The Cl vertebra is atypical in that it is composed of anterior, posterior, and bilateral arches; on the superior aspect of each lateral arch is an articulating surface for the occipital condyles (Figure 3). The C2 vertebra (axis) has transitional morphology, with characteristics similar to both the Cl vertebra above and the C3 to C7 vertebrae below (Figure 4). The odontoid projects cephalad from the superior aspect of the C2 vertebral body, and is tightly approximated to the inner surface of the anterior arch of Cl by the transverse ligament (Figure 5) (this complex is the most important structure in preserving stability of the atlanto-axial joint). The odontoid serves as the pivot point for Cl to C2 rotation.

Ligaments, Discs, and Joints The skull and vertebrae are connected by ligaments, indiscs, and interfacet joint capsules to provide the neck with a stable yet flexible framework. The seven major ligaments listed in Table 1 and depicted in Figure 6 are oriented longitudinally and preserve bony alignment of the spinal column during movement (these vary in tensile strength according to patient age, ligament type, and cervical tervertebral

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Disc <

Lateral view of the osseous articulation of two lower cervical vertebrae. (Reprinted with permission.“)

FIGURE 2.

segment location).

At the Cl to C2 articulation

the thick

transverse ligament courses behind and inserts on the pos-

terior aspect of the odontoid, and is the most important of the four ligamentous supports of the odontoid (termed the cruciate ligament complex) in preserving stability of the atlanto-axial complex (Figure 5). Intervertebral discs provide support to the spinal column during bending, and absorb up to 80% of compression loads applied to the cervical spine.12 Each intervertebral disc has four components: the interior nucleus pulposus, two cartilaginous end-plates on opposing (superior and inferior) vertebral body surfaces, and the annulus fibrosus. Facets and interfacet joints limit flexion and absorb approximately 20% of compression loads applied to the cervical spine. l2 The interfacet joint has a typical synovial membrane and fibrous capsule.

Vertebral Articulation As depicted in Figure 6, all of the cervical vertebrae articulate in the same general manner. The vertebral bodies are connected anteriorly by the anterior longitudinal ligament and intervertebral disc, and posteriorly by the posterior longitudinal ligament. The transverse processes are connected

Anterior Arch

Articular Facet / For Odontoid Process

Transverse Process

p&J-Y/‘

ylasnaen

Lamir ra

ii \ j

w 1ii,, h L \\vp

Spinous Process

FIGURE 1. Anatomy of a typical cervical vertebra.

Superior Articular Facet FIGURE 3.

,rch Anatomy of C 1 (atlas).

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TABLE1. The Ligamentous Supports of the Cervical Spine Anterior and posterior longitudinal ligaments join adjacent vertebral bodies and intervertebral discs. lnterspinous and supraspinous ligaments join adjacent spinous processes. lntertransverse figaments join adjacent transverse processes. Ligamenturn flavum joins adjacent laminae. lnterfacet capsular ligaments join adjacent facets.

Normal Range of Motion

Process FIGURE 4.

Anatomy of C2 (axis).

by the intertransverse ligaments. The vertebral arches are connected by the facet capsules and ligaments of the interfacet joints, and the ligamentum flavum. The spinous processes are connected by the supraspinous and interspinous ligaments. Figures 7 and 8 show cervical vertebral alignment in anteroposterior and posterior-oblique projections, respectively.

The occipito-atlanto-axial complex functions to support the head and protect the spinal cord and adjacent vital structures while allowing the neck a physiologic range of motion. The occiput to Cl articulation permits 15” of cervical flexion/ extension, 8” of lateral bending, and no rotary motion. 12*16,17 The Cl to C2 articulation permits 15” of flexion/extension and 50” of axial rotation (this joint accounts for 50% of total cervical rotary motion). The combined movement of the C3 to C7 vertebrae permits 60 to 75” of flexion/extension and accounts for the additional 50% of cervical rotary motion. ‘* Lateral bending of 10” to 12” occurs at each cervical segment between C2 to C5, and 4” to 8” at the C7 to Tl articulation.‘* The cervical spinal canal is lengthened during flexion and shortened during extension.13 Under normal conditions, the ligaments permit very little motion between vertebrae. In adults, the maximum extent of A-P mobility between Cl and C2 can be up to 3 mm; extension beyond this limit consistently results in rupture of the transverse ligament. 18*19 In younger-aged children, the maximum extent of anteroposterior mobility between Cl and C2

BIOMECHANICS Ligamenturn / Flavum

A thorough understanding of spinal kinematics is essential to conceptualizing the mechanisms and manifestations of traumatic CSI. The stability of the spinal column depends on maintaining spatial and functional relationships between vertebrae such that there is no damage to, or compromise of, the neurovascular structures (spinal cord and nerve roots) resulting in neurologic deficit or incapacitating pain. The details of this subject are extensively reviewed elsewhere’2-‘5; some of the more essential aspects are reiterated here.

Facet Capsular I Ligament

‘Interspinous Ligament

Odontoid Process

Supraspinous Ligament

AnferiorLongitudinal Ligament

FIGURE 5. ment.

Cl to C2 articulation

+ transverse

ligament attach-

1 I Ill

FIGURE 6. Multi-layered section of cervical spine anatomy with anterior and posterior compartments delimited by posterior longitudinal ligament.

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FIGURE 7. Normal alignment of cervical vertebrae in anteroposterior projection.

can be up to 5 mm due to a relative laxity of the transverse ligament.” Between two adjacent lower cervical vertebrae anteroposterior mobility usually does not exceed 3.5 mm, and angular displacement with flexion/extension usually does not exceed ll”.” The greatest degree of mobility at each of the cervical spine joints in children is age dependent, being located at C2 to C3 in those younger than 8 years, C3 to C4 in those aged 3 to 8 years, C4 to C5 in those aged 9 to 11 years, and CS to C6 in those aged 12 to 15 years.” In cadaver studies of the neonate it has been shown that the spinal column can be longitudinally stretched approximately 2 inches without disruption, while the spinal cord itself can be stretched only about 0.25 inches before rupture occurs.21

The Two-Compartment Theory To conceptualize its response to applied stresses, the cervital spinal column can be anatomically divided into two compartments by the posterior longitudinal ligament (Figure 6)22:

The anterior compartment contains all structures anterior to the posterior longitudinal ligament: anterior longitudinal ligament, vertebral body, and intervertebral disc. These components act as a tension band to limit extension and as a support system to prevent excessive flexion. The posterior compartment contains all structures posterior to the posterior longitudinal ligament: pedicles, facets, interface1 joints, facet joint ligaments, transverse processes, laminae, spinous processes, interspinous and supraspinous ligaments, and ligamentum flavum. These components act as a tension band to limit flexion and as a support system to prevent excessive extension. If one considers the posterior longitudinal ligament as the anatomic “still point” for flexion and extension motion, it then becomes apparent that a simultaneous reciprocal re-

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FIGURE 8.

Normal alignment of cervical vertebrae in

posterior-oblique projection.

sponse of anterior and posterior compartments occurs during applied flexion and extension stresses to the cervical spine, as depicted in Table 2. Flexion and extension forces result in “mirror image” lesions to the anterior and posterior compartments of the cervical spine; a specific description of TABLE2. Two-Compartment Reciprocal Response of the Cervical Spine to Flexion and Extension Forces Flexion Force Compression of the anterior compartment Distraction posterior

+ of the compartment

Extension Force Distraction of the anterior compartment

+ Compression of the posterior compartment

each type of lesion will be subsequently given in part II. In general, it is predominantly on the integrity of the posterior compartment (whose components form the surrounding support system for the spinal cord) that the stability of the cervical spinal column depends. An understanding of these biomechanics can often aid in determining the nature of the traumatic event that was responsible for the CSI.

THE PEDIATRIC CERVICALSPINE It is important to distinguish the unique characteristics of the pediatric cervical spine as a function of patient age. Table 3 lists the characteristics of the cervical spine in those younger than 8 years of age. 23,24 These anatomic features can predispose to an increased susceptibility for (1) hyperextension

and hype@exion

injuries due to greater

elasticity

WILLIAM A. BONADIO n CERVICAL SPINE TRAUMA IN CHILDREN

TABLE3. Anatomic Characteristics of the Pediatric Cervical Spine (Especially Prominent in Children Younger Than 8 Years) Hypermobility due to laxity of intervertebral ligaments, disc annulus, and transverse ligament of the odontoid Horizontal orientation of articular surfaces of vertebral bodies, facet joints, and uncinate processes Anterior wedging of vertebral bodies (especially prominent at C3) Presence of epiphyses Incomplete ossification of odontoid with a cartilaginous base Relatively large and heavy head with underdeveloped neck musculature

of ligaments and joint capsules; (2) subluxation due to horizontal orientation of vertebral bodies, facets, and uncinate processes; (3) fracture due to relative weakness of cartilaginous structures compared with ligaments (eg, fracture of the odontoid usually occurs prior to disruption of the transverse ligament); and (4) high cervical lesions due to the C2 to C3 anatomic fulcrum of cervical spine. In children older than 8 years of age the cervical spine acquires adult characteristics, making for more effective resistance of externally applied stresses that”*26 (1) anterior wedging of vertebral bodies disappears; (2) articulating planes of the facets become more vertically oriented, changing from 30” to 60” in the upper cervical spine and 55” to 70 in the lower cervical spine; (3) uncinate processes increase in vertical height; and (4) ligaments and facet capsules increase in tensile strength. RADIOGRAPHIC

EVALUATION

OF THE CERVICAL

SPINE

Accurate radiographic evaluation of the cervical spine is essential in the clinical assessment of possible CSI. The conventional radiographic series routinely evaluated in trauma cases is the three-view plain film analysis, which includes the cross-table lateral (CTL) neck view, anteroposterior neck view, and anteroposterior open-mouth view. The ancillary radiographic studies that can augment the ability to define cervical spine anatomy are discussed below. Limitations

of Radiographic

Evaluation

“One view = no view” is a common dictum regarding the ability of plain film radiographic analysis to “clear” the patient of risk for CSI.*’ Although the CTL neck view is the single most effective radiograph in identifying CSIs, up to 15% of spinal lesions are not evident on this view alone.*’ On CTL neck view it can be difficult to clearly visualize lesions at both the Cl to C2 segment (Jefferson fractures, nondisplaced or laterally displaced fractures of the odontoid, rotary subluxations of Cl to C2) and the C6 to C7 segment (due to muscle spasm, overlap of bony and soft tissue structures of the shoulder). In a series of patients with cervical spine injuries, all lesions that were not identified on CTL neck view were visualized on either anteroposterior neck view or anteroposterior open-mouth view.29 It is, therefore, essential to obtain a minimum three-view plain film radiographic analysis that clearly exhibits all aspects of all seven cervical vertebrae in two dimensions when

evaluating

for cervical

spine injury. If this complete

series

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cannot be adequately obtained during outpatient evaluation, cervical spine immobilization in neutral alignment should be maintained until proper radiographic evaluation is accomplished. The absence of radiographic abnormalities on three-view analysis does not necessarily eliminate risk for CSI. Since

soft-tissue structures vital to maintaining stability of the spinal column (ligaments, facet joints, discs) and the spinal cord itself are not visible on plain film radiography, injury to these elements can usually only be inferred by the presence of indirect evidence, like osseous malalignment, prevertebral soft-tissue swelling, avulsion fracture, or neurologic deficit. Therefore, any evidence of CSZ, whether it be clinical or radiographic, should be considered indicative of an unstable lesion until proven otherwise, and should prompt immediate neurosurgical consultation. In a series3’ of preadolescent

children (younger than 8 years of age) with severe spinal cord injury, 67% manifested the syndrome of spinal cord injury without radiographic abnormality (SCIWORA [ie, traumatic myelopathyl). In 50% of cases spinal cord lesions were complete, and in 52% of cases the onset of paralysis was delayed from the time of initial evaluation. A specific example of this phenomenon is the “central cord syndrome,” which results from hyperextension injury, causing buckling of the ligamentum flavum and circumferential “pinching” of the cord with neurologic deficit (cervical spine radiographs in these cases often do not exhibit abnormalities). This emphasizes the importance of maintaining immobilization of the cervical spine in neutral alignment whenever the clinical condition is in any way suggestive of cervical spine injury despite a normal three-view radiographic analysis. Radiographic

Analysis

A methodic, stereotyped routine must be used in assessing the four general aspects of cervical spine radiographic appearance, which are termed the “ABC’S”3’ (A, alignment; B, bones; C, cartilage; and S, soft tissues). Alignment. On CTL neck view, assess longitudinal alignment of the four smooth lines of lordotic curvature to the (1) anterior vertebral body margins, (2) posterior vertebral body margins (defining the anterior aspect of the spinal canal), (3) anterior margin of the bases of the spinous processes (defining the posterior aspect of the spinal canal), and (4) tips of the spinous processes (Figure 9). The laminae should align from C2 to C7 like “shingles on a roof ‘*‘; widening along the anterior spinal canal line can indicate facet dislocation. Assess longitudinal alignment for step-offsisubluxations (the upper limit of normal vertebral malalignment is <3 mm), and for straightening or reversal of the normal lordotic curvature (may indicate muscle spasm associated with CSI). The superior tip of the odontoid should align with the anterior margin of the foramen magnum. On anteroposterior neck view, assess symmetry of longitudinal alignment of vertebral bodies, facets, pillars, and spinous processes of C2 to T3 (stepoffs, subluxations, malalignments, or directional changes are abnormal). On anteroposterior open-mouth view assess alignment of the atlanto-occipital and atlanto-axial joints, the margins of the lateral arches of Cl with C2, and symmetric positioning of the odontoid between the interior margins of the lateral arches of Cl.

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the C2 vertebral body) above the level of the glottis and is usually less than 14 mm (or about equal to the anteroposterior diameter of the C3 vertebral body) below the level of the glottis.32 In general, the normal anteroposterior diameter of prevertebral soft tissues below the level of the glottis is double that above the glottis. An abnormal degree of widening of prevertebral soft tissues may be indicative of hemorrhage/ edema associated with an anterior compartment structure injury (eg, disruption of the anterior longitudinal ligament), and can sometimes be the solitary radiographic manifestation of an anterior cervical spine lesion.32 Ancillary

Radiographic

Studies

The performance of ancillary radiographic studies may be useful when the standard three-view analysis fails to adequately define cervical spine anatomy or substantiate the presence of a cervical spine lesion in a symptomatic patient; for example: The anteroposterior open mouth view is usually not possible to perform on a noncompliant young child; also, it can be difficult to clearly visualize the odontoid on this view in compliant older children because of superimposed central incisor teeth and the occipital skull. The Water’s view is performed to allow visualization of the odontoid “through” the foramen magnum. Flexion and extension (stress) views can exhibit subluxation or other instability of vertebral body or facet articulation due to ruptured ligaments. Supine oblique views can more clearly define the posterolateral aspects of vertebral bodies, pedicles, laminae, and intervertebral foraminae.

(11

(2)

0)

FIGURE 9. Normal lordotic curvature and alignment of cervical vertebrae. (Reprinted with permission.3’) Bones. On CTL neck view evaluate vertebral bodies for loss of axial height, abnormal degree of anterior wedging (in children there should be <3 mm difference in height between anterior and posterior aspects),32 and fracture. On anteroposterior neck view assess for loss of axial height of vertebral bodies (indicative of a burst compression fracture). Examine each of the pedicles, facets, laminae, and spinous processes for fracture. On anteroposterior open-mouth view assess the odontoid and lateral arches of C 1 and C2 for fracture. Cartilage. On CTL and anteroposterior neck views assess for uniformity of height and length of disc and interfacet spaces. Soft tissues. On CTL neck view evaluate anteroposterior diameter and configuration of prevertebral soft tissues (radiographic exposure must be during the inspiratory phase of respiration), which in young children is usually less than 7 mm (or about two thirds of the anteroposterior diameter of

Thin-secfion tomography (<3- 5-mm sectioning) of the cervical spine in anteroposterior and/or lateral projections can augment anatomic definition, especially at the Cl to C2 segment. In one series, thinsection tomography revealed lesions in 40% of patients with CSI and neurologic deficit whose standard three-view analysis was interpreted as normal, and disproved the existence of lesions suspected on three-view analysis in 25% of cases.33

5. Computerized tomography and magnetic-resonance imaging of the cervical spine are useful modalities in defining soft tissue details (especially disc and spinal cord morphology), anatomic relationships of structures in proximity to the spinal canal, and the location of foreign bodies. In one series of adult trauma victims, computerized tomography was 97% to 100% sensitive in identifying lesions of the cervical spine.4,34735 It must be understood that the first three ancillary radiographic studies listed above require positioning of the head and neck from neutral alignment, and should only be performed under direct physician supervision in patients who are fully alert and compliant and manifest no neurologic deficit or preceding radiographic abnormalities. Stress views should never be performed if there is any preceding clinical or radiographic evidence of CSI (especially vertebral body

WILLIAM A. BONADIO m CERVICAL SPINE TRAUMA IN CHILDREN

fracture), since maneuvering of the head and neck from neutral alignment can exacerbate or induce spinal cord compression and neurologic compromise. REFERENCES 1. Garfin S, Shackford S, Marshall L: Care of the multiply injured patient with cervical spine injury. Clin Orthop 1989;239: 19 2. Bohlman H: Acute fractures and dislocations of the cervical spine. J Bone Joint Surg 1979;61-A:1119 3. Rogers W: Fractures and dislocations of the cervical spine. J Bone Joint Surg 1957;39-A:341 4. Gerrelts B, Petersen E, Mabry J, et al: Delayed diagnosis of cervical spine injuries. J Trauma 1991;31 :1622 5. Dietrich A: Pediatric cervical spine fractures: Predominantlv subtle oresentation. J Pediatr Sura 1991:26:995 6,‘Guthkeich A, Fleisher A: Patterns of cerv/cal spine injury and their associated lesions. West J Med 1987;147:428 7. Huelke D, O’Day J, Mendelsohn R: Cervical injuries suffered in automobile crashes. J Neurosurg 1981;54:316 8. Kewalramani L, Kraus J, Sterling f-l: Acute spinal cord lesions in a pediatric population: Epidemiologic and clinical features. Paraplegia 1980;18:206 9. Hill S, Miller C, Kosnick E: Pediatric neck injuries: A clinical study. J Neurosurg 1984;60:700 10. Henrys P, Lyne E, Lifton C: Clinical review of cervical spine injuries in children. Clin Orthop 1977;129:172 11. Rachesky I, Boyce T, Duncan B, et al: Clinical prediction of cervical spine injuries in children. Am J Dis Child 1987;141: 199 12. Maiman D, Yoganandan N: Biomechanics of the cervical spine. In Black P (ed): Clinical Neurosurgery. Baltimore, MD, Williams 8 Wilkens, 1991, pp 543-570 13. Panjabi M, White A: Basic biomechanics of the spine. Neurosurgery 1980;7:76 14. Roaf R: A study of the biomechanics of spinal injuries. J Bone Joint Surg [Br] 1950;42-B:810 15. Panjabi M, White A, Johnson R: Cervical spine mechanics as a function of transection of components. J Biomech 1975;8: 327 16. Garber J: Abnormalities of the atlas and axis vertebraeCongenital and traumatic. J Bone Joint Surg 1974;49-A:1792

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