CHAPTER 30
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The Child with a Limb Deficiency
1585
knees. Traditionally, an articulating knee would be introduced
in a congenital amputee at approximately 3 to 4 years of age.
This age was determined, in part, by the limitations in the
size and function of the components. In the experience at the
authors’ center, as well as others, introduction of a prosthetic
knee without a locking feature can be used as the first pros-
thesis when the child first pulls to stand. A recent report dem-
onstrated the benefits of early fitting with articulated knees in
children as young as 17 months. All children learned to walk
with an articulated knee, despite their age differences (157).
As the child develops and grows, more sophisticated con-
trol systems (e.g., hydraulic knees) can be incorporated into the
prosthesis. Most components carry specific weight guidelines,
and many children reach these ranges well before adulthood.
For example, an adult hydraulic polycentric knee is routinely
used on 8-year-old boys whose weight has surpassed 100 lb.
This does not mean that every child of a certain age and weight
should have a particular knee. Placing a sophisticated knee and
control system on an individual who has neither the hip range,
muscle strength, nor residual limb length to activate the knee
often results in contralateral hip and lower back pain as well as
patient frustration.
Prosthetic Feet.
Variations in the materials, design, and
alignment of the foot can have profound effects on the perfor-
mance of the prosthesis. Functionally, prosthetic feet can be
categorized into five main groups (226):
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Solid ankle cushion heel (SACH)
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Single axis
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Multiaxis
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Elastic keel
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Dynamic response
The SACH foot [Therapeutic Recreation Systems, Inc. (TRS)]
contains no articulating parts, and foot motion depends on the
various compressive properties of the materials used between
heel-strike and toe-off (Fig. 30-52A). It is generally considered
when amputees require maximum late-stance stability because
of weak knee extensors, knee-flexion contractures, or poor mid-
to late-stance balance (227). The SACH foot is used in pedi-
atrics when the foot size is below 12 cm. The Little Feet is a
bolt on type SACH foot designed with unique energy dynamics
(Fig. 30-52B). The toes are very flexible because of the use of
an elastomer that more closely mimics the child’s foot. A special
removable heel core allows the foot to be used “barefoot.”
The single-axis foot usually contains rubber bumpers that
allow passive dorsi- and plantar flexion. By changing the hard-
ness of the bumper, the prosthetist is able to effectively change
the properties of the foot. The single-axis foot does not come
in a size suitable for the child amputee. This foot is best suited
for the transfemoral amputee, in whom full-foot contact with
the ground is necessary to increase stability. The multiaxis
foot allows passive dorsi- and plantar flexion, inversion, and
eversion. The multiaxis foot was once thought best suited for
the amputee who because of uneven terrain or a lifestyle that
includes golfing or various sports requires flexibility and some
rotational control: It has now found its way into the pediat-
ric population. The multiaxial foot (College Park Truper foot)
(Fig. 30-52C) allows controlled resistance in all planes—inver-
sion/eversion, dorsiflexion and plantar flexion, and transverse
rotation about the ankle joint. This class of foot has gained
wide acceptance within the pediatric arena, in part because of
its ability to absorb forces at the ankle and reduce transmission
of these forces to the socket. This is particularly useful when
fitting a very short residual limb.
Once the child’s activity level warrants a higher function-
ing foot, the prosthetist can move the child into a dynamic-
response foot. This group of feet is distinguished by a spring
mechanism in the keel that deflects during gait (Fig. 30-52D).
The dynamic-response foot has found its way into competi-
tive-level sports as well as day-to-day activities. Although the
variety of componentry for children is still much less than for
adults, there is a wide variety of feet with different perfor-
mance characteristics available. It is important to use compo-
nents that will maximize performance and at the same time be
appropriate for the patient (228).
0
10
20
30
40
70
90
100
50
60
FIGURE 30-51.
Four-bar linkage is an internal polycentric knee that
provides many advantages to the patient, including increased stabil-
ity and better ground clearance during swing phase. As indicated in
this illustration, the point of rotation varies with the degree of flexion.
With the knee flexed, the leg folds under the thigh segment and there-
fore is very useful for longer residual limbs. There is also a hydraulic
version of the four-bar linkage for children.
