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Patients with concomitant oc-cipitalization of the atlas or basilar impression accompanying instabili-ty of the upper cervical spine are more likely to have symptoms of an-terior cord co

Cervical Spine Instability

in Children

Abstract

The upper cervical spine begins at the base of the occiput, continues caudally to the C2-C3 disk space, and includes the occipitoatlantal and atlantoaxial joints Nontraumatic upper cervical spine instability can result from abnormal development of osseous or ligamentous structures or from gradually increasing ligamentous laxity associated with connective tissue disorders Such instability can lead to compression of the spinal cord during movement of the cervical spine Establishing a correct diagnosis includes performing a thorough physical examination as well as evaluating radiographic relationships and measurements

Appropriate management of syndromes associated with instability

of the upper cervical spine includes preventive care and recommendations for sports participation Surgical treatment for the upper cervical spine includes a posterior surgical approach, used for instability, and the use of rigid plate implants, wiring, and bone graft materials to achieve a solid spinal fusion

The upper cervical spine runs from the occiput to the C2-C3 disk space and includes the occipi-toatlantal and atlantoaxial joints

Nontraumatic instability of this seg-ment is relatively rare in the pediat-ric population However, familiarity with the effective evaluation and treatment of upper cervical spine in-stability is important because per-manent neurologic compromise can result from this condition Addition-ally, orthopaedic surgeons who un-derstand the unique aspects of the developing upper cervical spine are better able to make sports participa-tion recommendaparticipa-tions for children with conditions such as Down syn-drome

Nontraumatic upper cervical spine instability can result from the abnor-mal development of osseous or

liga-mentous structures Alternatively, in-stability can develop as a result of the gradually increasing ligamentous lax-ity associated with connective tissue disorders Instability resulting from either cause can lead to compression

of the spinal cord during movement

of the cervical spine Such compres-sion may be present at the occipitoat-lantal joint, atlantoaxial joint, or both Instability of the upper cervical spine

in a child presenting clinically is largely variable and can range from a complete absence of signs and symp-toms to frank quadriparesis For ex-ample, in Down syndrome, radio-graphic evidence of instability in an asymptomatic patient is a common finding; by contrast, in Morquio’s syn-drome, myelopathy frequently ac-companies radiographic evidence of upper cervical instability

Brian P D Wills, MD

John P Dormans, MD

Dr Wills is Resident, Department of

Orthopedics and Rehabilitation,

University of Wisconsin, Madison, WI.

Dr Dormans is Chief of Orthopaedic

Surgery, The Children’s Hospital of

Philadelphia, Philadelphia, PA, and

Professor of Orthopaedic Surgery,

University of Pennsylvania School of

Medicine, Philadelphia.

None of the following authors or the

departments with which they are

affiliated has received anything of value

from or owns stock in a commercial

company or institution related directly or

indirectly to the subject of this article:

Dr Wills and Dr Dormans.

Reprint requests: Dr Dormans, The

Children’s Hospital of Philadelphia,

Second Floor, Wood Building, 34th and

Civic Center Boulevard, Philadelphia,

PA 19104.

J Am Acad Orthop Surg

2006;14:233-245

Copyright 2006 by the American

Academy of Orthopaedic Surgeons.

Instability of the upper cervical

spine often is accompanied by other

pathology involving the structures

in this anatomic region, including

spinal stenosis, basilar impression,

occipitalization of the atlas,

Klippel-Feil syndrome, and central nervous

system abnormalities (eg,

Arnold-Chiari syndrome malformation)

In-stability of the upper cervical spine

and stenosis often are two major

fac-tors in the development of

myelopa-thy Neurologic signs and symptoms

can result from any of a

constella-tion of anomalies that may be

present in a child with instability of

the upper cervical spine Further,

such instability also is associated

with a number of syndromes and

conditions, such as those related to

ligamentous laxity or abnormal

bone development In such

instanc-es, these cervical anomalies may be the first indication of other organ ab-normalities, which should be evalu-ated with appropriate screening strategies Because orthopaedic sur-geons often are the first to evaluate these patients, the surgeon should begin such assessment with a full history and clinical examination; fo-cusing only on the neck may delay accurate diagnosis of other condi-tions

Developmental and Functional Anatomy

Much has been learned recently about the development of the mam-malian spine An example is the

dis-covery that homeobox (Hox) genes

play a significant role in regulating the development of the axial and ap-pendicular skeletons These genes di-rect the embryonic differentiation and segmentation along the cranio-caudal axis by activating and repress-ing various DNA sequences and en-coding transcription factors and proteins.1Development of the base of the skull, the basiocciput, is similar

to that of the atlas (C1) and axis (C2): all arise from medial and lateral com-ponents of sclerotomes and the perinotochord in a manner that dif-fers from the remainder of the verte-bral column The basiocciput2 devel-ops from somites 1 to 4, whereas the atlantoaxial column develops from somites 5 to 7 (Figure 1) Organogen-esis occurs simultaneously with de-velopment of the axial skeleton This temporal relationship explains, in part, the frequent association re-ported between spinal and visceral anomalies It is important to be aware of these potentially associated anomalies to ensure that they are identified and treated appropriately The atlas develops from three os-sification centers, one for each

later-al mass (present at birth) and one for the body (developing by age 1 year) The posterior arches fuse at age 3 to

4 years; the lateral masses fuse to the body by age 7 years3(Figure 2) The axis is formed from five primary os-sification centers: two lateral

mass-es, two vertically oriented halves of the dens, and the body Two second-ary ossification centers include the tip of the odontoid (ossiculum ter-minale) and the inferior ring apophy-sis The odontoid process is

separat-ed from the body by the dentocentral synchondrosis, which closes be-tween the ages of 5 and 7 years4 (Fig-ure 2) Orthopaedic surgeons should know these ossification centers and the approximate ages at which they fuse so that sites of bone growth are not mistaken for fractures during ra-diographic evaluation

Stability at the atlanto-occipital junction is provided by the cup-shaped joints between the occipital

Figure 1

Embryologic development of the spine Unsegmented presomitic mesoderm (PSM)

matures into somites, pairs of segments on either side of the future spinal cord, in

a process called somitogenesis The somites further differentiate into sclerotome,

which forms the adult vertebrae, and dermomyotome, which forms the axial

musculature and also contributes to the adult dermis This maturation occurs in a

craniocaudal direction as shown by the coronal section on the right The three axial

views to the left demonstrate the stages of maturation (Reproduced with

permission from Tracy MR, Dormans JP, Kusumi K: Klippel-Feil syndrome Clin

Orthop 2004;424:187.)

condyles and the superior articular

facets of C1, as well as by the

capsu-lar ligaments that surround and

an-chor these joints The tectorial

membrane, a continuation of the

posterior longitudinal ligament, also

provides considerable support At

the atlantoaxial joint, the bony

in-tegrity of the odontoid process and

the integrity of the transverse

liga-ment provide most of the support

Paired alar ligaments connect the

odontoid to the occipital condyles,

and together with the apical

liga-ment, which runs from the odontoid

to the foramen magnum, act as

sec-ondary stabilizers and check

liga-ments during rotation5(Figure 2)

The mobility of the cervical spine

at the occipitoatlantoaxial complex

can be separated into

flexion-extension, lateral bending, and

rota-tion In the mature spine, range of

motion between the occiput and the

atlas is 15° in flexion-extension, 10°

in lateral bending, and negligible in

rotation.5Between the atlas and axis,

range of motion is 10° in flexion and

extension, negligible in lateral

bend-ing, and 50° in rotation.5The

biome-chanics of the developing cervical

spine, which are likely to change

during maturation of the cervical

spine, have not been fully studied

Clinical Presentation

and Evaluation

Children with instability of the

up-per cervical spine may present for

any of a number of reasons The

or-thopaedic surgeon often is consulted

to evaluate children with syndromes

or conditions known to have

fre-quent involvement of the

muscu-loskeletal system, as well as to

assess children with incidental

ra-diographic findings of cervical spine

anomaly In such cases, the surgeon

should evaluate the cervical spine as

part of the initial evaluation,

includ-ing orderinclud-ing flexion-extension

radio-graphs Occasionally, patients will

present with a history of head or

neck trauma, neck pain, torticollis,

loss of neck range of motion, or

oth-er clear signs of uppoth-er spinal cord in-volvement More often, however, the presentation of this involvement

is less obvious, and the constellation

of signs and symptoms may lead the surgeon to sites of spinal cord com-pression (Table 1)

Frequently, multiple tracts in the spinal cord are involved along with associated vertebral artery and cere-bellar signs and symptoms, which can make locating the site of com-pression difficult Perovic et al6

re-ported on a series of children with instability of the atlantoaxial joint, a condition in which the earliest sign

of myelopathy is a gradual loss of physical endurance, which occurs before signs of pyramidal tract in-volvement This development of progressive weakness with the ab-sence of other neurologic findings is especially frequent with the instabil-ity of the upper cervical spine

report-ed in Morquio’s syndrome

With posterior cord impinge-ment, changes in proprioception and

Figure 2

Anatomy and ossification centers of the atlas (A) and axis (B) C, The relationship

of the apical, alar, and transverse ligaments to the odontoid (Reproduced from

Copley LA, Dormans JP: Cervical spine disorders in infants and children J Am Acad

Orthop Surg 1998;6:204-214.)

pain perception, as well as vibratory

sense, can occur as a result of the

in-volvement of the posterior spinal

columns When the cerebellum is

involved, ataxia, incoordination, and

nystagmus also may be observed

Posterior cord compression can be

caused by the posterior rim of the

fo-ramen magnum or the posterior ring

of C1 In addition to spinal cord

involvement, vertebral artery

com-pression, which can occur without

spinal cord involvement,7,8can lead

to syncopal episodes, decreased

mental acuity, dizziness, and sei-zures Patients with concomitant oc-cipitalization of the atlas or basilar impression accompanying

instabili-ty of the upper cervical spine are more likely to have symptoms of an-terior cord compression resulting from odontoid impingement.7,9 Damage to the anterior pyramidal tracts can result in muscle weakness and atrophy, pathologic reflexes (eg, hyperreflexia, spasticity, clonus), and ataxia.7,9 Indentation of the brainstem has been found at autopsy

to result from the abnormal odon-toid.9

Cranial nerve involvement may result from instability of the upper cervical spine Compression of the lower cranial nerves as they exit the medulla may occur from the insta-bility itself or from associated anom-alies, such as basilar impression or Arnold-Chiari malformation.10The cranial nerves involved most often are the trigeminal (V), glossopharyn-geal (IX), vagus (X), accessory (XI), and hypoglossal (XII) However, in-volvement of other cranial nerves has been reported.9,10

Given the wide range of

neurolog-ic signs and symptoms that may be seen in a patient with instability of the upper cervical spine, it is impor-tant to perform a complete and thor-ough neurologic examination and to clearly document results at each pa-tient visit Subtle changes between clinical visits may be the first sign of impending spinal cord compromise

Radiographic Assessment

Initial imaging to evaluate for insta-bility of the upper cervical spine should include lateral neutral, an-teroposterior, and open-mouth odon-toid views Flexion-extension views should be obtained only when the spine is clearly stable and there is no recent history of trauma The rela-tionship of the foramen magnum to the atlas and odontoid can be mea-sured by the McGregor, McRae, Chamberlain, Wackenheim, and Wiesel-Rothman lines as well as by the Power ratio (Figure 3) McRae’s line often is the easiest to discern for basilar invagination because the an-terior and posan-terior rims of the fora-men magnum usually are visible on radiographs, regardless of film qual-ity McRae’s line connects the poste-rior rim of the foramen magnum to the anterior lip of the most caudal aspect of the foramen magnum (the basion) Chamberlain’s line is drawn from the posterior aspect of the hard

Table 1

Possible Neurologic Findings of Upper Cervical Spine Instability

Posterior spinal column

involvement

Changes in pain, proprioception, vibratory sense

Anterior spinal column

involvement

Muscle weakness and atrophy, pathologic reflexes (hyperreflexia, spasticity, clonus), ataxia

Cerebellar involvement Nystagmus, ataxia, incoordination

Vertebral artery compression Syncopal episodes, decreased mental

acuity, dizziness, seizures Cranial nerve involvement

III (oculomotor) Ptosis, diplopia, strabismus

V (trigeminal†) Decreased facial sensation, weakness

with mastication

VII (facial) Paralysis of muscles of facial

expression, loss of taste VIII (vestibulocochlear) Vertigo, nystagmus, hearing loss

IX (glossopharyngeal†) Dysphagia, absent gag reflex

X (vagus†) Hoarseness, dysphagia, dysphonia,

decreased gag reflex, uvular deviation, cardiac and gastrointestinal abnormalities (parasympathetic input)

XI (accessory†) Paralysis of sternocleidomastoid and

trapezius XII (hypoglossal) Asymmetrical tongue protrusion

* It is common for children to present with combinations of findings.

† Cranial nerves most commonly affected

palate to the posterior rim of the

fo-ramen magnum McGregor’s line is

drawn from the most caudad point

of the occipital curve of the skull to

the posterior edge of the hard palate

Wackenheim’s line runs down the

posterior surface of the clonus, with

its inferior extension just touching

the posterior tip of the odontoid The

atlantodens interval (ADI), the space

between the posterior aspect of the

anterior ring of C1 and the anterior

border of the odontoid, should be

<4 mm in children younger than age

8 years and become <3 mm in

chil-dren age 8 years and older through

adulthood11,12 (Figure 3) The ADI

measures maximally in flexion and

can decrease in extension; therefore,

measurements should be performed

for both positions Children with

chronic instability at the

atlantoax-ial joint often have an ADI that is

in-creased In these instances, the space

available for the spinal cord (SAC)

should be measured Steel’s rule of

thirds should be used at C1, with the

odontoid, the spinal cord, and

addi-tional space each occupying one

third of the spinal canal.11

In 2001, Wang et al13 evaluated

the development of the pediatric

cer-vical spine radiographically, thus

providing reference values to

objec-tively assess the developing cervical

spine, including the SAC Their data

show that the spinal canal markedly

increases in diameter from birth to

age 8 years; growth then slows but

continues through adolescence In

contrast, the ratio of canal diameter

to the corresponding vertebral body

width linearly decreases from birth

through adolescence.13 Because

ca-nal diameters are correlated between

adjacent levels, comparing the canal

diameter above and below the

sus-pected anomalous vertebrae is a

highly sensitive approach to

detect-ing spinal stenosis when it is

sus-pected

Interpretation of plain

posteroan-terior and lateral radiographs can be

difficult in patients with conditions

such as spondyloepiphyseal

dyspla-Figure 3

Lateral craniometry A, Lines used to determine basilar invagination and

measurements of atlantoaxial instability ADI = atlantodens interval, SAC = space

available for the spinal cord B, Method for calculating the Wiesel-Rothman line for

atlanto-occipital instability A line connecting the anterior and posterior arches of the atlas (points 1 and 2, respectively) is drawn Two perpendicular lines to this line are then drawn, one through the basion (the line intersecting point 3) and the other through the posterior margin of the anterior arch of the atlas The distance (x) between these lines should not change by more than 1 mm in flexion and extension

C,The Power ratio is calculated by drawing a line from the basion (B) to the posterior arch of the atlas (C) and a second line from the opisthion (O) to the anterior arch of the atlas (A) The length of line BC is divided by the length of line

OA A ratio≥1.0 demonstrates anterior atlanto-occipital dislocation (Reproduced from Copley LA, Dormans JP: Cervical spine disorders in infants and children

J Am Acad Orthop Surg 1998;6:204-214.)

sia because the

mucopolysacchari-doses have abnormal bone

Radio-graphs of a child with multiple

congenital anomalies of the upper

cervical spine can be equally

chal-lenging to interpret; however,

mag-netic resonance imaging (MRI) can

be effective in diagnosing anomalies

with instability of the upper cervical

spine MRI provides the additional

benefit of allowing evaluation of the

spinal cord and other soft tissues,

in-cluding the spinal ligaments and

disks, which can be only indirectly

evaluated by computed tomography

(CT) Dynamic MRI, in which

imag-es are taken with the cervical spine

in flexion and extension, can provide

evidence of cord compression in

pa-tients who have signs and symptoms

suggestive of cord compression but

have normal plain radiographs.14CT

also is useful to visualize osseous

anomalies of the upper cervical

spine that are difficult to interpret

using plain radiographs In addition,

CT has been used dynamically to

evaluate instability.15Occasionally,

fluoroscopy and cineradiography

also are indicated

When evaluating the pediatric cervical spine radiographically, it is important to keep in mind a number

of features that are unique to the de-veloping spine Increased neck mo-tion is seen in children younger than age 10 years for the following rea-sons: relative ligamentous laxity, rel-ative muscle weakness, incomplete ossification of cartilaginous ele-ments, wedge-shaped vertebral bod-ies leading to decreased cervical lor-dosis (Figure 4), a more horizontal orientation of shallow facet joints, or decreased tensile strength of liga-ments and facet capsules.16

Apparent subluxation, termed pseudosubluxation, may be observed

in radiographs of the cervical spine

of healthy children Pseudosublux-ation at C2-C3 (and less commonly

at C3-C4) measuring up to 4 mm can

be seen in 40% of children younger than age 8 years with normal cervi-cal spines.16Also, when comparing flexion-extension radiographs, a pseudosubluxation should reduce in extension, whereas an actual sublux-ation will be maintained because of guarding and muscle spasm Cattell

and Filtzer16also noted that, during extension in young children, appar-ent overriding of anterior arch of the atlas relative to the odontoid may occur (Figure 4) This is a result of the nonossified ossiculum

termina-le and also of the anterior body of C1, which may be only partially os-sified, depending on the child’s age

Syndromes and Conditions Associated With Instability

Children with one or more of the syndromes and conditions

frequent-ly associated with anomalies and in-stability in the upper cervical spine should be routinely followed to pre-vent neurologic compromise (Table 2) Aside from the careful attention that must be given to the upper cer-vical spine, it also is important to maintain a high index of suspicion for serious underlying pathology in any child presenting with

atraumat-ic neck pain and/or signs of myelop-athy The threshold for ordering cer-vical spine radiographs in these cases should be exceedingly low

Conditions Associated With Connective Tissue

Abnormalities

Down syndrome (trisomy 21) oc-curs in 1 in 700 to 1,000 live births and is associated with a number of medical conditions, including con-genital heart disease and leuke-mia.17 Instability of the cervical spine at both the atlanto-occipital and atlantoaxial levels, and hyper-mobility at one or both of these lev-els, is common However, most of these patients remain

asymptomat-ic In a prospective study of 236 chil-dren with Down syndrome, instabil-ity at C1-C2 was noted in 17% of patients; however, only 18% of these patients were reported to be symp-tomatic Thus, approximately 3% of children with Down syndrome, most of whom will present between the ages of 5 and 15 years, develop symptomatic atlantoaxial

instabili-Figure 4

A,Lateral neutral radiograph of a normal cervical spine in a 3-year-old child Note

the wedge-shaped vertebral bodies and apparent high-riding atlas B, Lateral

neutral radiograph of a normal cervical spine in a 40-year-old patient for

comparison The vertebral bodies are rectangular in shape, and the anterior arch of

the atlas no longer appears to override the odontoid

ty.18Orthopaedic surgeons generally

agree that children with Down

syn-drome who have overt symptomatic

instability of the upper cervical

spine should undergo surgical

stabi-lization Preoperatively, all potential

levels of instability should be

evalu-ated Before undertaking a

stabiliza-tion procedure, we obtain

flexion-extension MRI scans in all patients

with suspected instability of the

up-per cervical spine in order to look for

dural sac impingement

In the asymptomatic patient with

upper cervical spine instability,

indi-cations for surgical stabilization are

less clear At our institution,

poste-rior arthrodesis is usually performed

on asymptomatic Down syndrome

patients with >8 to 10 mm of

atlan-toaxial instability and dural sac

im-pingement on flexion-extension

MRI However, before proceeding

with arthrodesis in Down syndrome

patients with significant

asympto-matic upper cervical spine

instabili-ty, the importance of individualized

patient assessment in deciding

whether to perform occipital

cervi-cal arthrodesis cannot be

overem-phasized Postoperative

complica-tions such as incision and pin-site

infection, and a reported 60% rate of

pseudarthrosis,19are more common

in patients with Down syndrome

than in the general population.19

The connective tissue defects

re-ported in Marfan syndrome result

from abnormalities in the protein

fibrillin, predisposing patients to

lig-amentous and bony abnormalities in

the cervical spine These defects also

predispose patients to increased risk

of dissecting aortic aneurysm,

ectop-ic lentis, and kyphoscoliosis In a

prospective series, atlantoaxial

hy-permobility was noted in 18% of

pa-tients and basilar impression in

36%.20 Similarly, patients with

Ehlers-Danlos syndrome (EDS),

par-ticularly type IV, may develop

insta-bility of the upper cervical spine

be-cause atlantoaxial subluxation has

been reported in two of three

pa-tients with this type of

Ehlers-Danlos syndrome.21 Although Lar-sen syndrome is more commonly associated with cervical spine ky-phosis, which responds to early pos-terior spinal fusion, these patients also may develop instability of the upper cervical spine resulting from

the underlying ligamentous lax-ity.22

It also is important to evaluate for cervical stenosis when assessing a child with known ligamentous lax-ity because the space available for the spinal cord is affected by both

Table 2

Conditions Associated With Pediatric Upper Cervical Spine Instability

Syndromes Down syndrome (trisomy 21) Skeletal dysplasias

Kniest dysplasia Chondrodysplasia punctata Metaphyseal chondrodysplasia Diastrophic dysplasia

Kozlowski spondylometaphyseal dysplasia Metatropic dysplasia

Spondyloepiphyseal dysplasia congenita Pseudoachondroplasia

Campomelic dysplasia Mucopolysaccharidoses Morquio’s syndrome Maroteaux-Lamy mucopolysaccharidosis syndrome Hurler syndrome

Mucopolysaccharidosis VII Klippel-Feil syndrome Marfan syndrome Hajdu-Cheney syndrome Goldenhar syndrome DiGeorge syndrome (22q11.2 deletion syndrome) Larsen syndrome

Ehlers-Danlos syndrome Shprintzen-Goldberg craniosynostosis syndrome Dyggve-Melchoir-Clausen syndrome

Marshall-Smith syndrome Weaver syndrome Spondylocarpotarsal synostosis syndrome Others

Infectious/Inflammatory Conditions Pyogenic atlantoaxial rotatory subluxation (AARS; Grisel syndrome) Juvenile rheumatoid arthritis

Juvenile ankylosing spondylitis Others

Conditions With Acquired Instability Trauma

Os odontoideum Cerebral palsy Others

stenosis and instability In our

expe-rience, children with ligamentous

laxity often have secondary cervical

spine stenosis, a result of spinal cord

compression both from the

instabil-ity and from an underlying tight

spi-nal caspi-nal

Skeletal Dysplasias

The skeletal dysplasias are a

col-lection of more than 200 conditions

that have in common abnormalities

in the development and remodeling

of bone and cartilage Dysplasias that

commonly involve the cervical spine

are spondyloepiphyseal dysplasia,

di-astrophic dysplasia, Kniest dysplasia,

chondrodysplasia punctata,

metatro-pic dysplasia, and metaphyseal

chon-drodysplasia Patients with a skeletal

dysplasia should undergo a skeletal

survey and flexion-extension lateral

cervical spine radiographic views

during the initial visit to screen for

the osseous anomalies.23

The mucopolysaccharidoses are

included in the International

Classi-fication of Skeletal Dysplasias.24

These include Morquio’s syndrome,

in which odontoid aplasia or

hypo-plasia causing C1-C2 instability is

nearly universal; however, the

insta-bility can be effectively treated by

posterior occipitocervical

arthrode-sis.25 In our experience, patients

with Morquio’s syndrome with

C1-C2 instability nearly always require

surgical fusion of C1 to C2 or of the

occiput to C2 when the arch of C1 is

incompetent, or when or there is

oc-cipitalization of C1

For children with instability of the

upper cervical spine and an

underly-ing diagnosis of skeletal dysplasia,

the patient evaluation and treatment

algorithm used is similar to that used

for children with syndromes of

liga-mentous laxity Before any surgical

stabilization procedure, children

with radiographic evidence of

insta-bility of the upper cervical spine

should undergo flexion-extension

MRI to assess any spinal cord

im-pingement

Inflammatory and Infectious Conditions

Instability of the upper cervical spine can result from the inflamma-tory reaction that follows adenoton-sillectomy and from other conditions that cause swelling of the soft tissues around the upper cervical spine Oc-casionally, pyogenic atlantoaxial ro-tatory subluxation (AARS; Grisel’s syndrome) leading to atlantoaxial in-stability can result from adenotonsil-lectomy because of pathogens enter-ing the periodontoid vascular plexus after the procedure With early recog-nition, isolation of the infectious or-ganism and treatment with appropri-ate antibiotics, and immobilization

of the cervical spine, most patients fully recover At our institution, pa-tients with inflammatory AARS of less than 1 week’s duration are usu-ally treated with nonsteroidal anti-inflammatory medication and fitted with a loose hard cervical collar un-til symptom resolution When the AARS does not improve after 1 week, the patient is admitted for soft-halter traction Patients with AARS that persists for >4 weeks are treated with traction until resolution followed by

a cervicothoracic orthotic or halo ring and vest; skeletal traction may

be needed to obtain resolution for these more resilient or for delayed presentation cases At the occipito-cervical junction, tuberculosis infec-tion leading to instability also has been reported and should be consid-ered in the differential diagnosis, es-pecially in children with a history of international travel or with high-exposure risk.26

Children with juvenile rheuma-toid arthritis may present with an increased ADI as a result of inflam-mation of the transverse ligament and erosion of the odontoid because

of synovial hypertrophy As a result

of chronic inflammation, lateral ra-diographs may show an apple core appearance of the odontoid in pa-tients with long-standing juvenile rheumatoid arthritis Actual insta-bility is uncommon in this

popula-tion, and neck pain and neurologic manifestations are infrequently as-sociated with juvenile rheumatoid arthritis The thinning of the odon-toid does, however, make it more susceptible to fracture.27

Juvenile ankylosing spondylitis most commonly presents with the sacroiliac joint and back pain or with peripheral arthritis Atlantoaxial in-stability occurs infrequently, even in patients with chronic juvenile anky-losing spondylitis However, atlanto-axial instability has been described

as a presenting manifestation.28 Thus, when patients with juvenile ankylosing spondylitis complain of neck pain or similar symptoms, in-stability of the upper cervical spine should be considered

Klippel-Feil Syndrome

Klippel-Feil syndrome is charac-terized by congenital fusions and anomalies of the cervical spine.29 Stenosis also is commonly seen in the cervical spine of these patients; the combination of stenosis and in-stability is the major factor in the de-velopment of myelopathy Klippel-Feil syndrome often is associated with other musculoskeletal and or-gan anomalies, including scoliosis and renal and cardiac maldevelop-ment Renal ultrasound and echocar-diogram should be performed on these children for further assessment Auditory anomalies, neurologic ab-normalities (synkinesis, or uncon-scious mirror movements), and skel-etal anomalies (Sprengel’s deformity, cervical ribs) also may be present The classic clinical presentation is

a triad of low posterior hairline, short neck, and limited neck mobility; however, this triad occurs in less than half of patients with Klippel-Feil syndrome.30 Patterns of malforma-tion associated with a high risk for instability are those that limit cervi-cal motion at one level; these include atlanto-occipital fusion with C2-C3 block vertebrae, abnormal atlanto-occipital junction with several distal block vertebrae, and a single open

in-terspace between two block

seg-ments.31 Children with these

pat-terns of malformation should be

monitored closely with annual

phys-ical examination and

flexion-extension plain radiographs until age

10 years, then followed every 2 to 3

years through adulthood (Figure 5)

Os Odontoideum

Trauma is thought to be the most

likely cause of os odontoideum

Damage to the basilar synchondrosis

results in the separation of the

odon-toid from the body of the axis.32

At-lantoaxial instability then develops

because the odontoid is not a

func-tional stabilizer These patients

of-ten present in late adolescence with

complaints of atraumatic local neck

pain Open-mouth odontoid views

demonstrate an oval ossicle located

in place of the normal odontoid

tip.32 CT is useful to confirm os

odontoideum when plain

radio-graphs are questionable

Management of

Nontraumatic Upper

Cervical Spine

Instability

Preventive Care, Injury

Prevention, and Sports

Participation

Patients with syndromes

associ-ated with instability of the cervical

spine (Table 2) should undergo

screening studies consisting of lateral

neutral, anteroposterior, and

open-mouth odontoid views Flexion and

extension views should be obtained

only when the patient is

neurologi-cally stable, there is no history of

re-cent significant trauma, and there are

no findings in the history or physical

examination to suggest gross cervical

spine instability These children

should be routinely seen by an

ortho-paedic surgeon for a careful history,

physical examination, and repeat

ra-diographs, in addition to regular

vis-its to the pediatrician Although

treatment should be individualized,

children younger than age 10 years

usually should be seen annually and then, from age 10 years through adulthood, every 2 to 3 years By age

10 years, the cervical spine has largely taken on adult characteristics, which decreases the likelihood that stability will develop

Patients with congenital syn-dromes, such as Morquio’s syndrome, may benefit from multidisciplinary care programs The orthopaedic sur-geon should educate patients and their families about the natural his-tory of the condition and potential medical problems, emphasizing that,

if any neurologic symptoms develop,

the child should be seen immediately

by a physician trained in the detec-tion of instability of the cervical spine (Table 1) Symptomatic patients should undergo additional workup, such as CT and MRI, in addition to plain radiographs Flexion-extension MRI should be obtained in sympto-matic patients who demonstrate in-stability on plain radiographs When these imaging studies demonstrate dural sac compression, spinal fusion usually is indicated

As discussed, asymptomatic pa-tients who initially present with ev-idence of instability are challenging

Figure 5

A and B, Lateral flexion-extension preoperative radiographs of a 3-year-old with

Klippel-Feil syndrome demonstrating a block vertebrae of C2-C3 and assimilation

of C1 with occiput The atlantodens interval is grossly widened, indicating instability

of C1-C2 C and D, Postoperative lateral flexion-extension postoperative

radiographs taken 16 months after occipitocervical arthrodesis demonstrating solid fusion of the occiput to C2-C3

to treat These children often have a

baseline ADI greater than is

accept-able for normal children, which

makes establishing a guideline for

prophylactic fusion difficult

Chil-dren with particular syndromes

as-sociated with instability of the upper

cervical spine, such as Down

syn-drome, will remain unstable but

asymptomatic throughout their

life-times Other conditions, such as

Morquio’s syndrome, frequently

have progressive instability;

there-fore, these patients should undergo

preventive fusion before neurologic

symptoms develop However, most

patients fall somewhere between

these two ends of the spectrum in

terms of risk for developing

symp-tomatic instability Thus, for those

in whom upper cervical spine

insta-bility is suspected, determining the

degree of instability at the initial

vis-it is important in order to make

baseline radiographic

measure-ments, which are then repeated at

each follow-up visit and compared

with the baseline Patients whose

upper cervical spine instability is

progressing are candidates for

pre-ventive surgical stabilization

Sports participation remains

con-troversial for children with

asympto-matic instability of the cervical

spine Children with congenital

fu-sions resulting from Klippel-Feil

syndrome are in this category For

such children, contact sports and

sports that involve excessive

bend-ing; twistbend-ing; or axial loading of the

neck, such as diving and gymnastics,

could lead to catastrophic

neurolog-ic injury We recommend that

chil-dren with demonstrated instability

of the upper cervical spine be

dis-couraged from participating in these

high-risk activities, although the

de-cision to participate in these sports

must be made on an individual basis

In addition, patients who have

un-dergone surgical stabilization of the

cervical spine should not participate

in high-risk sports

In 1983, the Special Olympics

mandated cervical spine screening

with plain lateral and flexion-extension views in all Down syn-drome patients participating in high-risk sports However, the American Academy of Pediatrics Committee

on Sports Medicine has concluded that “lateral plain radiographs of the cervical spine are of potential but un-proven value in detecting patients at risk for developing spinal cord injury during sports participation.”33 In-stead, the committee recommended,

as the greater priority, identifying pa-tients with signs or symptoms con-sistent with symptomatic spinal cord injury.33In our opinion, children with possible upper cervical spine instabil-ity should be screened radiographi-cally for several reasons.34Screening radiographs not only allow for assess-ment of cervical spine instability but also establish a baseline for future reference; thus, screening radiographs allow for evaluation for possible con-genital bony anomalies Further-more, they provide reassurance for families of patients with normal studies They also provide helpful in-formation for patients with poor communication skills or those un-able to cooperate with a history and physical examination.34

Surgery

The posterior surgical approach, which allows for cord decompres-sion when that is indicated, is most commonly used for treatment of in-stability of the upper cervical spine

Several techniques of stabilization using rigid plate implants, wiring techniques, and bone graft materials have been described For isolated at-lantoaxial instability, the technique

of Brooks-Jenkins is the most com-monly used method of arthrodesis at our institution.35Recently, transar-ticular C1-C2 fixation with facet screws has been reported with good results in a large series

predominant-ly made up of adults, but including some children.36However, this pro-cedure historically has not been per-formed in children, and there are no reported pediatric series The

prox-imity of the vertebral artery and C2 spinal nerve makes transarticular C1-C2 fixation technically demand-ing, and the relatively small bone mass of C1 and C2 in young children greatly increases risk to these struc-tures In skeletally mature children, however, transarticular facet screws provide rigid fixation and in selected cases may eliminate the need for halo ring and vest immobilization after arthrodesis The use of lateral mass plates and screws for rigid in-ternal fixation may be appropriate, especially in older children and when the lower cervical spine will

be incorporated into the fusion Patients with occipitoatlantal in-stability and those in that group with atlantoaxial instability who require more extensive fusion (ie, because of

a coexisting incompetent posterior atlantal arch or occipitalization of C1) are treated with occipitocervical arthrodesis Two techniques of occip-itocervical arthrodesis (Figures 5 and 6) have been developed, both of which can be adapted for abnormal osseous anatomy seen in some con-genital conditions.37,38 Instrumenta-tion using a Luque rectangle, as well

as other methods of rigid internal fix-ation using screws with rods and/or plates, also have been described.39 Al-though their use is usually indicated only in the setting of an intraspinal tumor or infectious process, tech-niques involving anterior or transoral approaches for upper cervical spine instability in children have been de-scribed In children with a history of intraspinal tumor or with a condition

in which future MRI is anticipated, the use of MRI-compatible titanium instrumentation is preferred to stain-less steel because the ferromagnetic properties of stainless steel can make future MRI studies difficult to inter-pret.40

For intraoperative positioning and prolonged postoperative cervical spine immobilization, the halo ring and vest offer better immobilization and positioning with fewer skin complications They also allow for