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Nontraumatic Upper
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.
T
he 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 recommendations 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.
Volume 14, Number 4, April 2006 233
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.
1
Development 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 basiocciput

2
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 years
3
(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 years
4
(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.)
Nontraumatic Upper Cervical Spine Instability in Children
234 Journal of the American Academy of Orthopaedic Surgeons
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 rotation
5
(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.
5
Between the atlas and axis,
range of motion is 10° in flexion and
extension, negligible in lateral bend-

ing, and 50° in rotation.
5
The 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 ordering 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 upper 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 al
6
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. JAmAcad

Orthop Surg 199 8;6:204-214.)
Brian P. D. Wills, MD, and John P. Dormans, MD
Volume 14, Number 4, April 2006 235
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,
7,8
can 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.
10
The
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 posterior 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
Site of Compression Signs and Symptoms*
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
II (optic) Visual disturbances
III (oculomotor) Ptosis, diplopia, strabismus
IV (trochlear) Diplopia when looking downward
V (trigeminal
†
) Decreased facial sensation, weakness
with mastication
VI (abducens) Diplopia
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
Nontraumatic Upper Cervical Spine Instability in Children
236 Journal of the American Academy of Orthopaedic Surgeons
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
adulthood
11,12
(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 al
13
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.)
Brian P. D. Wills, MD, and John P. Dormans, MD
Volume 14, Number 4, April 2006 237
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.
14
CT
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.
15
Occasionally,
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.
16
Also, 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 Filtzer
16
also 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.
Nontraumatic Upper Cervical Spine Instability in Children
238 Journal of the American Academy of Orthopaedic Surgeons
ty.
18
Orthopaedic 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,
19
are 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
Brian P. D. Wills, MD, and John P. Dormans, MD
Volume 14, Number 4, April 2006 239
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 canal.

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. W ith 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 or thotic 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-
Nontraumatic Upper Cervical Spine Instability in Children
240 Journal of the American Academy of Orthopaedic Surgeons
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 multidisciplinar y
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.
Brian P. D. Wills, MD, and John P. Dormans, MD
Volume 14, Number 4, April 2006 241
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; twisting; 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 .
33
In our opinion, children with
possible upper cervical spine instabil-
ity should be screened radiographi-
cally for several reasons.
34
Screening
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.
35
Recently, 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.
36
However, 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
Nontraumatic Upper Cervical Spine Instability in Children
242 Journal of the American Academy of Orthopaedic Surgeons
more freedom of mandibular motion
compared with the Minerva cast. In

infants and very young children, a
CT scan of the head before halo ap-
plication can help to avoid cranial
sutures and other thin areas in the
skull during pin placement. In in-
fants, the halo should be held in
place with 8 to 12 pins inserted at
low torque (2 in-lb), and the pin in-
sertion angle should be perpendicu-
lar to the skull.
41
In older children
and adults with normal bone quali-
ty, four to six pins usually are insert-
ed, with a torque of 6 to 8 in-lb. At
our institution, children who have
upper cervical fusions usually are
immobilized in a halo ring and vest
until radiographic bony union. This
belt-and-suspenders approach in-
creases the likelihood of successful
union, especially in children who
may not be fully compliant. Others,
however, have reported successful
osseous union without the use of the
halo ring and vest, particularly when
Luque rectangle or transarticular
screw fixation are used.
42,43
Infection

of anterior pin sites is the most com-
mon complication from this method
of immobilization.
44
Comparative evaluation of halo
pin design and of the accuracy and re-
liability of torque wrenches from var-
ious manufactures has demonstrated
that wide-flanged, short-tipped halo
pins are optimal for use in the imma-
ture skull. In addition, spring-type
wrenches may have a design advan-
tage over adjustable wrenches for
halo application in children.
45
It is
important to remember that time to
bony union may be prolonged in
some syndrome and inflammatory
conditions; patients should remain
immobilized until solid fusion is doc-
umented radiographically.
Summary
Nontraumatic upper cervical spine
instability in children can be chal-
lenging to recognize because the pre-
sentation can be variable. Further,
such instability is often accompa-
nied by other bone pathology as well
as by central nervous system abnor-

malities. To effectively evaluate
such instability in children, the or-
thopaedic surgeon must have a thor-
ough understanding of the develop-
mental anatomy and history and
also perform a physical examination
that does not focus solely on the
neck.
Nontraumatic upper cervical
spine instability is associated with a
number of syndromes and condi-
tions, such as Down syndrome, in
which radiographic evidence of in-
stability in an asymptomatic pa-
tient is a common finding. Instabil-
ity is also associated in such
conditions as Klippel-Feil syndrome
and stenosis; the two may lead to
myelopathy. Skeletal dysplasias of
the cer vical spine include spondy-
loepiphyseal dysplasia, diastrophic
Figure 6
Wiring technique for occipitocervical arthrodesis using iliac crest graft. A, Four burr holes are drilled into the occiput, and a
trough is fashioned into the base of the occiput to accept the unicortical autograft. Luque wires are passed through the burr
holes and looped on themselves. Wires are placed either sublaminar or through the spinous process of C2 or C3. The graft is
contoured to lock in precisely. B, The wires are then crossed, twisted, and cut. The patient is immobilized in a halo ring and vest
until solid fusion occurs. C, Occipitocervical fusion technique using autologous rib graft and 16-gauge wires. (Panels A and B
adapted with permission from Dormans JP, Drummond DS, Sutton LN, Ecker ML, Kopacz KJ: Occipitocervical arthrodesis in
children. J Bone Joint Surg Am 1995;77:1236-1237. Panel C adapted with permission from Cohen MW, Drummond DS, Flynn
JM, Pill SG, Dormans JP: A technique of occipitocervical arthrodesis in children using autologous rib grafts. Spine

2001;26:826.)
Brian P. D. Wills, MD, and John P. Dormans, MD
Volume 14, Number 4, April 2006 243
dysplasia, Kniest dysplasia, chon-
drodysplasia punctata, metatropic
dysplasia, and metaphyseal chon-
drodysplasia. Instability also can re-
sult from the inflammatory reaction
that follows adenotonsillectomy
and other conditions that cause
swelling of the soft tissues around
the upper cervical spine, as well as
in os odontoideum, in which pa-
tients present with atraumatic local
neck pain. CT is useful to confirm
when plain radiographs are ques-
tionable.
The posterior surgical approach,
which allows for cord decompres-
sion, is most commonly used to
treat instability of the upper cervical
spine. Techniques include use of rig-
id plate implants, wiring, and graft
materials. For isolated atlantoaxial
instability, the technique of Brooks-
Jenkins is commonly used.
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Volume 14, Number 4, April 2006 245
Nontraumatic Upper Cervical Spine Instability in Children
246 Journal of the American Academy of Orthopaedic Surgeons