[,n,q.nxrNcro Ger AnouNn
The physicalcharacteristicsjust listed not only help explain why motor
developmenrmay be delayed but, in addition, help explain unusual
movement strategies that are often seen in children with
achondroplasia. Many children with achondroplasiado not pass
through the customary stagesof ambulatory developmentthat lead to
iearninghow to walk. Often, a child's chosenmethodsof gettingaround
causeworry for parents,and often for the child's doctors,too. Both
physicii ns and parents tend to expect a particular sequenceof
development in all babies. This includes, for example, traditional,
reciprocalcrawling. [Crawling on handsand kneesseemsso universal
that, in fact, a discredited and untrue theory postulatedthat children
who failed to learn to crawl would have, as a consequence,serious
developmentaland behavioral problems later in life.l
But many children with achondroplasiachoose alternative methods
of getting around.Many never crawl in the traditional fashion.Indeed,
only about 20Voof children with achondroplasiaever crawl in that
traditional way. Crawling often is not a very efficient way to get around
tbr a child with achondroplasia.Short arms and short legs meansthat
children with achondroplasiawho try to crawl in the traditional way
rnay find that their plump bellies are still dragging on the floor. And,
traditionai crawling requires a child to be able to hold the head up.
Becausechildren with achondroplasiahavelzrge andheavyheads,as
weli as hypotonia and instability of the neck, holding the headup in a
crawling position for an extendedperiod is difficult.
Instead,many infants and young children with achondroplasiachoose
alternative strategies that circumvent the problems that arise with
traditional crawling. Many may choose 'snowplowing', 'reverse
snowplowing'or'spider crawling'.
I
In both snowplowingandreversesnowplowingthe large,heavyhead
servesas a balancing tool while the legs and feet push the child
forward:
I
I
snowplowing
reversesnowplowing
More than half of children with achondropiasiachooseto snowplow
at somepoint and nearly half usereversesnowplowingas a way of
moving from place to place.
Spider crawling is almost never
seen in children of average
stature but is used by about a
quarter of children with
achondroplasia.Spidercrawling,
in contrast to traditional
crawling, which is on the hands
and knees,involves support by
the handsandfeet. Although the
head needs to be supported,
spider crawling more easily
allows the belly to be cleared
tiom the floor.
PosrrroNTuNsrtrons
The combinationof short limbs, excessivelymobile hips and'trunk,
unstable knees and a large head often results in children with
demonstratingunusual,but adaptive,ways of getting
achondroplasia
from sitting to standing.Children of averagestaturemost often will
transition by first going to a squatting or kneeling position and then
standing up. In contrast,many children with achondroplasialearn to
'jackknife'.
spider crawling
In addition to theseunusualmethodsof getting around,many children
with achondroplasiawill show long preference for army crawling,
logrolling or seatscooting.Logrolling may be particularly common in
children with achondroplasia(and is the preferredmeansof locomotion
logrolln0
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stabilization
and
muscle strength
in the arms and
legs.Likewise,
afm}
CfaWling
allows the weight
to be distributed
to the hands,
arms, stomach,
legs and feet and
allows the head to be periodically restedon the floor; this is probably
helpt'ul in a child with hypotonia, joint hypermobility and a heavy
head.
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Jackknifing begins with the child
fully extending the legs while
sitting. Next, bending only at the
waist, the body is fully flexed and
the head is placed on the floor.
Using the head for balance, the
child next wedges up over fully
extendedlegs- pushingwith the
legs, followed by extensionof the
torso. Remarkably, this results in
transition from sitting to standing
without everbendingtheknees.We
suspectthat this strategyis chosen
principally because of the
instability of the knees seen in
many children with achondroplasia. Jackknifing allows
transition with the knees straight
and locked, while rising from a
kneel or squat requires dynamic
stabilization of the knees something that is very hard for
many childrenwith achondroplasia.
'Wedgingup'is a
somewhat lessdesirable method of
t ra n- siti oni ng to
s t a ndi ng. Some
children will push
one leg our straight
and then use that
one straight leg ro
support all of the
body's weight in
getting to stand.
U n f or tun ate ly,
wedging up over one leg seemsto increasethe chanceof progressive
soft tissue instability at the knee and may make more likely the need
for surgicai intervention.
Dressingand undressingmay posea problem as well becauseof limb
shortening,limited elbow extension,a prominent bottom and a heavy
head. Some children
learn unusualways of
surmounting such
problems, taking advantage of trunk mobility to compensate
for ttreshortreach,and
figuring out a way to
stabilize the head at
the sametime.
Frun Moron Sru,ls
children with achondroplasiaoften useunusualmethodsto hold writing
implements. Becauseof the child's short fingers, the excessive
separationbetween the middle and ring fingers and hypermobility of
the finger joints, often crayonsor pencits win be used with a twofinger or four-finger grip rather than the more traditional pencil grip.
Thesegrips, while 'abnormal',are,in fact, adaptiveand shouldnot be
discouraged.Many adultswith achondroplasiausea two-finger method
without sacrificing quality or efficiency of handwriting.
Scissorsalsomay be problematic.
In addition to the hand
characteristics
described,children
with achondroplasiaoften have
excessiveelbow pronation(palm
down) and either limitation or
reluctanceto useelbow supination
(palm up). Such supination is
necessaryfor traditional scissor
use.
WHBn CeN I Expncr Mv Cnu,D To......
Principailybecause
of variousphysicalfeatures,
childrenwith achondroplasianot only have someunusualadaptiveways to perform
motor tasks,but, overall show delaysin attainingmany developnrentalskills.Suchdelaysusuallydo not reflectcognitivelimits.
The tablelists certainmilestonesthatparentsoftenobserve,the averageageat which averagestaturedchildrenattaintheseskills and
the rangesof agewithin which most childrenwith achondroplasia
accomplishthe sameskills.
Range (in Months)
for Children with
Achondroplasia
(25th-90th Voile)
Sit, without support*
Pull to stand
Stand alone
Walk
Reach
Passobject
Bang 2 objects
Scribble
9 - 20.5
1 2 -20
1 6 -29
1 4 -27
6 -15
8.5 -1 4
9-1 4
15-3 0
AverageAge in
Average Statured
Children (in
Months)
).)
7.5
11.5
t2
3.5
6
8.5
13.5
To CBISBRATE
PaLetits,pirl,sicilrrt, cariy chiklhooil eclucatol'sriltii thelapists
shoulcl i'cccignizciilai the dillercjntlltoveiliunr stratcqiesexhibited
by a cliiicl rr,'iih;rcituticlioirlasia are
r r ( ) t t r s t t l l l l ) ' i i , . ': t r r q i l {}l ' w ( }fr }/ l l ( ) f
should tirei' be tiiuugirt of as abrloftttill.Tirt- cirii'-ris sirnlily adaptirrg to liis .ri'hi-r plivsicii dift-ercnccs. ln iucl. lire:,ririiitl, of chilch'enrvith aulioiitii'uirlasiirtu invent
and utiiizc ulteciiri,- aitciiiative
rrraysof doiirg il.riirgsiciiccts thcir
i'cstrurccti|lnc)ssaii(l problern sr-rlviirg skills and, tlreii,is sornething
to t'clebrotc.
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*We activcly tiiscouage
unsuppoftd sitting prior to ar le6r 12- 14 months of age tn babies with rchotrdroDlasia.
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(ithr-r R(.;ourcas:
If your child's development is substantially outside of the ranges
given you shouldtalk more with your child's physician.
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