Keywords Down's syndrome - articular instability - atlanto-axial joint - radiography
Palavras-chave síndrome de Down - instabilidade articular - articulação atlanto-axial - radiografia
Introduction
The Down Syndrome (DS) or Trisomy 21 is a genetic syndrome characterized by a chromosomal
abnormality (extra 21 chromosome). It was initially described in 1866 by Sir John
L. H. Down, as the first chromosomal abnormality detected in human kind and may occur
in three ways: Free trisomy, translocation or mosaicism[1 ]
[2 ].
Out of the several orthopedic changes found in this syndrome, the Atlantoaxial Instability
(AAI) is critical for otorhinolaryngology, and it is represented by a mobility that
is higher than the normal of two upper cervical vertebrae C1 and C2[2 ]. This occurs due to the insufficiency of the transverse ligament, the main stabilizer
of the flexo-extension movements between the first and the second cervical vertebra
and abnormality of the anatomy of this articulation[3 ].
The incidence of AAI in patients with DS varies from 10 to 30%[3 ]
[7 ], it is asymptomatic in most of these individuals and only in 1 to 2% of the cases
of AAI diagnosis we found signs and/or symptoms of such change, such as: cervical
discomfort, abnormal gait, change to the sphincter control, lesion of the upper motor
neuron, paralysis and death[4 ]
[7 ]. About 80% of the symptomatic patients evolve to chronic instability. AAI may be
preceded by a cervical trauma, damages caused by sport, orotracheal intubation and
head and neck surgery[5 ]. Urgent evaluation and treatment is required for symptomatic patients and regular
follow up with the physician associated to the prevention of cervical traumas is crucial
for asymptomatic individuals.
The definite diagnosis of cervical spine instability may be difficult. AAI may be
detected through the distance between the infero-posterior face of the C1 anterior
arc and the anterior process of the odontoid in lateral flexion or extension radiographies,
with a limit of up to 4.5 mm[8 ]. The patient with DS who has this measure exceeded will have restrictions for performance
of physical activities. However, there may be problems in the AAI radiographic tracking,
like: inadequate radiological technique and lack of accuracy to the atlantoaxial distance[6 ]
[7 ].
The objective of this work is to check the prevalence of Atlantoaxial Instability
in thirty patients with Down Syndrome who undergo service follow-up in the Clinical
Hospital of the UFPR [Federal University of Paraná] and review the need to carry out
routine cervical radiography in the patients with prescription to otorhinolaryngologic
surgery.
Method
We performed a prospective study in the population of individuals with Down Syndrome
in follow up at the Clinical Hospital of UFPR, in the city of Curitiba, in 2008.
The study was approved by the Ethics Committee in Research of the Clinical Hospital
of UFPR.
The parents or persons responsible for the children were duly informed and contacted
about the objective of the research and which exam would be made with diagnostic purpose.
30 patients were selected including 13 (43.3%) male and 17 (56.7%) female whose age
ranged from 2.5 years to 15 years with a mean age of 9 years old.
Upon authorization of the parents we carried out the application the questionnaire
that registered any type of symptomatology presented by the patient: general health
state, presence or not of cervical discomfort or torticollis, gait abnormalities,
spasticity, paralyses, members weakness, change of sphincter control, previous history
of trauma, orotracheal intubation, cervical surgery, recurrent UAI, sports activity.
In addition to details of the motor development.
The patients were submitted to radiographic exam of the cervical spine according to
the praxis used in the Radiology discipline of the Clinical Hospital and always reported
by the same researcher.
The complimentary exam used was the cervical radiography in the anterior, posterior,
profile, in flexion and extension for all patients. The radiographic criteria of instability
evaluation were based on the measure of the interval between the infero-posterior
face of the C1 anterior arc and the odontoid anterior process. We considered it to
be normal up to 4.5 mm, between 4.5 and 6 mm suggesting AAI and full AAI over 6 mm
at the atlanto-odontoid distance ([Figures 1 ] and [2 ]).
Figure 1. Neutral X-ray.
Figure 2. Flexion X-ray.
Results
Among the 30 patients with Down Syndrome evaluated through profile, in flexion and
extension and antero-posterior cervical spine radiography, we found all with the distance
between the infero-posterior face of the anterior C1 arc and the anterior process
of odontoid lower than 4.5 mm. Two patients had a distance on the upper limit of normality
and were asymptomatic. The average atlanto-odontoid distance in the population studied
was of 3.5 mm and there was no case of atlantoaxial instability.
Among the 30 patients submitted to the questionnaire on symptomatology we confirmed
that: 2 (6.6%) had cervical discomfort/torticollis, 5 (16.6%) had alterations of the
sphincter control (over 4 years of age) and 1 (3.3%) patient complained of pain from
the upper and lower ends. All had a delay in the motor development. Repetition airways
infection was observed in 50% of the patients.
However, there was no significant association between the signs and symptoms noticed
in these patients and the radiological measures.
The results are summarized in [Graphic 1 ].
Graphic 1. Complaints and symptoms presented.
Discussion
Non-traumatic AAI was first described by Berkheiser and Seidler in 1931; and the high frequency of atlantoaxial subluxation (AAS) in patients with
DS was described by Spitzer, in 1961.
Since 1983, the Members of the Medical Division of the Special Olympics, have determined
that all participants with DS must be evaluated by clinical and radiological exam
of the cervical spine so as to research the atlantoaxial instability, and if the atlanto-odontoid
distance is over 4.5 mm, such athletes must be left out of sports activities that
involve forced flexo-extension movements of the cervical spine, to prevent possible
neurological damages due to the medullar compression.
In 1995, the Pediatric American Academy inquired the validity of the AAI radiological
triage in DS because, besides the presence of symptomatic instability is rare, the
atlantoaxial distance generally regresses or stagnates in time.
Molin et al[9 ] confirmed that out of 36 patients with DS aged between 3 to 41 years old (16 of
the male sex and 20 of the female sex), only 5 cases, that is, 13.8% had AAI. Another
study, by Minatel et al[10 ], with 40 patients with DS, 15% of asymptomatic AAI were diagnosed with radiology
while 85% did not present with clinical-radiological evidence without limitation as
for the participation in physical education programs and sports activities.
A study carried out in Florianópolis by Nahas et al[1 ] researched the incidence of AAI in 17 children with DS aged between 5 and 15 years
old and asymptomatic AAI was diagnosed in 2 of them, that is to say, 11.76%. During
the work there was a confirmation in some children of neck extension or flexion limitation,
apathetic cervical posture, cervical hyperextensibility and reduction of the muscular
force and there was no clear association between the signs noticed and the radiological
measures.
Cros , Linares , Castro and Mansilla
[11 ] performed a study with 25 patients with DS that measured the atlanto-odontoid distance
(AOD) through radiographies of the cervical spine in flexion and profile followed
by computed tomography and tridimensional reconstructions. In 4.3% OAD was verified
equal or higher than 5 mm without variation between the measures in flexion and profile.
Through this research we conclude that the incidence of AAI has shown quite variable
findings of 19 to 30% according to the literature. Therefore, the need for deeper
researches on the subject is justified, since in this study the AAI incidence was
of 4.3%. Such data are compatible with the findings of this study, in which no atlantoaxial
instability was diagnosed in 30 patients with Down Syndrome submitted to cervical
spine radiography.
Morton et al[12 ], in a 5-year follow-up, did not find the development of AAI in the children studied
with admeasurements.
In a prospective study[13 ], of 1993, the practice of sports was seen not to influence the appearing of neurological
changes and exclusion of these patients from sports has no scientific base.
Taylor et al[14 ] concluded the diameter of the medullar canal has a stronger relevance for the AAI
evaluation than the atlantoaxial distance, and when the canal is smaller than 13 mm,
it suggests a higher risk of medullar lesion. The most adequate complimentary exam
to evaluate AAI is Computed Tomography and Magnetic Resonance may be also used. But
its use as screening is not frequent due to the need to provide anesthetic induction
and its high cost[15 ]
[6 ].
The AAI research in patients with DS, even asymptomatic ones, is recommended when
they had been submitted to intubation for general anesthesia or procedures that involve
hyperflexion or hyperextension of the neck or extreme rotation of the head[16 ].
In fact, the patients with Down Syndrome frequently need upper airways procedures,
such as: adenoidectomy and tympanostomy. During these procedures a suitable position
of the neck is required for the surgeon to operate, which consists of an important
extension of the cervical spine for adenoidectomy and rotation of 90 degrees for tympanostomy.
According to the literature review by Harley and Collins in 1994, it is strongly recommended that all patients submitted to otorhinolaryngologic
surgeries be submitted to a preoperative screening to check for AAI, which is justified
by the low cost of such screening[17 ]
[18 ]. Cohen ,[19 ], in turn, considers screening not to be cost-effective nor specific or reliable
to determine which individuals with AAI have a risk to develop subluxation or spinal
compression.
The literature does not provide a consensus as for the actual validity of the radiological
triage to research the Atlantoaxial Instability in all patients with Down Syndrome.
However, it suggests that doctors performing risk procedures in patients with Down
Syndrome (anesthesia, surgery with cervical manipulation like the otorhinolaryngological
procedure) must treat all as susceptible cases and take universal precautions[19 ].
Conclusion
The Atlantoaxial Instability is a peculiar alteration of the Down Syndrome to which
there is no scientific evidences of the need to request radiological routine such
as provided by the Medical Division of the Special Olympics.
New studies must be accomplished to define the actual importance of the AAI radiological
research in patients with DS and the regular clinical control should always be made
in search of the appearing of neurological alterations that form the main trace of
medullar compression in the presence of AAI.
