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Atlanto-axial instability or AAI describes an increased
flexibility between the first and second bones of the
neck. Most individuals with Down syndrome have some increased
flexibility of joints, called ligamentous laxity, which
can affect any of their joints. AAI refers to this condition
when it affects the joint between the first and second
cervical vertebrae.
Since the vertebrae surround and protect the spinal cord,
instability of the joint could place the spinal cord at
risk for injury.
Screening for AAI involves both x-rays and physical examination.
The physical examination looks for any changes that might
suggest pressure on the spinal cord. X-rays of the head
and neck are taken from the side (lateral view) with the
head in a normal position as well as with the head bent
forward (flexed) and tilted back (extended).
A space between parts of the first and second cervical
vertebrae (atlanto-dens space) of more than 5 millimeters
is considered suggestive of atlanto-axial instability.
85% of individuals with Down syndrome have no evidence
of atlanto-axial instability. 13-14% show evidence of
instability by x-ray only and have no symptoms. This is
called asymptomatic atlanto-axial instability. Only 1-2%
have symptoms that may require treatment. These individuals
are referred to as having symptomatic atlanto-axial instability.
Symptoms may include neck pain or persistent head tilt,
intermittent or progressive weakness, changes in gait
pattern or loss of motor skills, loss of bowel or bladder
control, increased muscle tone in the legs, or changes
in sensation in the hands and feet.
A child with symptoms that might be caused by pressure
on the spinal cord should be examined and x-rayed IMMEDIATELY!
Most physicians who are knowledgeable about children with
Down syndrome recommend that all children with Down syndrome
be screened with x-rays during the preschool years. Screening
before age 2 or 2 1/2 may be confusing because the bony
structures may not show up clearly.
If x-ray evidence of instability is found but the individual
has no signs or symptoms of spinal cord pressure after
careful examination by his/her physician, no special treatment
is needed.
The 13-14% of individuals who have asymptomatic atlanto-axial
instability require no special medical or surgical treatment.
However, these individuals may want to avoid activities
that may put extra strain on the neck. High risk activities
include gymnastics (especially tumbling and trampoline),
diving, swimming the butterfly stroke, high jump, soccer,
and collision sports (such as football). Individuals with
asymptomatic AAI should have more frequent medical and
x-ray follow-up.
For the 1-2% of individuals with symptomatic atlanto-axial
instability, surgical stabilization of the vertebrae is
necessary. Such surgery should be performed by a neurosurgeon
or orthopedic surgeon who is familiar with Down syndrome
and who has experience treating atlanto-axial instability.
Re-screening of the 85% group of children with Down syndrome
who have normal x-rays and no symptoms is a matter of
debate. However, since there have been reports of such
individuals who were later found to have AAI, a common
recommendation is to re-screen once each decade.
All individuals should be screened before surgery that
will involve the use of a breathing tube since there have
been rare reports of neck injury during placement of the
breathing tube.
Please quote fully and reference National Down Syndrome
Congress,
Prepared for and Approved By:
The Professional Advisory Committee,
National Down Syndrome Congress
January, 1991
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