1552
CHAPTER 30
|
The Child with a Limb Deficiency
or both. As the child grows, it is a good idea to begin shift-
ing some of the weight bearing to the proximal structures to
prepare the child for the time when full weight bearing on
the end may not be possible. Failure to shift weight bearing
proximally with age usually leads to fitting difficulties result-
ing from tolerance issues. This discomfort probably arises
from the small distal weight-bearing surface seen in many of
the congenitally deformed limbs. This may be partially alle-
viated with a Boyd amputation, which is generally broader
than the Syme amputation. This is an especially important
consideration in the bilateral amputee, in whom dispropor-
tionate weight shifting to the sound side is not possible for
comfort.
As with most amputations done at a young age, the con-
dyles will be small at the time of amputation, will not grow to
normal size, and therefore, do not require trimming as in the
adult. The proximal brim of the socket is designed with supra-
condylar (SC) medial and lateral trim lines, in an effort to con-
trol any knee valgus instability and/or patellar instability. The
type of suspension will depend on the size of the distal end of
the residual limb. If it is very large, an obturator or window
may be necessary. With further growth, the distal end may not
be sufficient for suspension, and a different design will be nec-
essary. These are discussed later.
To best utilize the current prosthetic feet in children who
are older and large enough to take advantage of them, it is nec-
essary that at least 4 cm of space be available at the distal end.
If the prosthetist is to offer the latest in energy-storing feet,
greater residual limb-length differences will be required. This
need can be anticipated, and an arrest of the distal or proximal
tibial and fibular physes performed at the appropriate time.
This length differential is usually not a problem in children
with congenital limb deficiency, because the deficient limb will
usually be shorter than the other limb. However, it can be an
issue in children with acquired deficiency treated by Syme or,
more often, Boyd amputations. Although the longer lever arm
of the Syme amputee tends to compensate for the lack of more
elaborate prosthesis components, when fit is possible, they can
be an advantage.
Authors Preferred Recommendations.
For patients
with a functional foot with at least 3 rays and a predicted
discrepancy of <20 cm, the authors suggest retaining the foot
with the goal of limb-length equalization. If the discrepancy
is projected to be 5 cm or less, a contralateral pan genu epi-
physiodesis at the appropriate time is the treatment of choice.
For greater discrepancies, limb lengthening is added to the
treatment plan. Lengthening is done with a monolateral
external fixator unless there is secondary angular or rotational
deformity that is being corrected at the same time. In those
cases, a circular fixator is preferred. A Boyd amputation is
suggested for patients with >17 cm of predicted discrepancy
or in patients with a nonfunctional foot. In rare instances
where the calcaneus is significantly hypoplastic, or if it is
proximally displaced in the posterior calf, a Syme amputation
is performed.
For patients with planned lengthening and distal femo-
ral valgus, the authors prefer to correct the valgus simultane-
ously with femoral lengthening. If no femoral lengthening is
planned and the deformity is >10 degrees in a patient with
at least 2 years of distal femoral growth remaining, a medial
distal femoral reversible hemiepiphysiodesis, with removal of
implants when the angulation has resolved. A distal femoral
angular osteotomy is reserved for the skeletally mature adoles-
cent with prosthetic fitting difficulties and genu valgum.
Tibial anteromedial bowing is corrected at the time of
amputation if it will interfere with prosthetic fitting. In the
authors’ experience, this is generally true if the angulation
is >30 to 40 degrees. In the young child who is undergo-
ing amputation at the same time, the authors fix the oste-
otomy by running the threaded Steinman pin that crosses the
calcaneus and tibia more proximally to fix the osteotomy and
engage the proximal anterior tibial cortex. For the older child,
we prefer crossed Steinman pin fixation Finally, fibular anlage
resection is reserved for the rare patient who has recurrent
anteromedial tibial bowing after osteotomy or progressive
bowing over time.
Pearls/Pitfalls.
The authors have treated several patients
who demonstrated a recurrent or progressive anteromedial tib-
ial bow after correction with osteotomy. In these cases, surgical
exploration with resection of the fibular anlage has proved a
successful treatment.
When initially evaluating the patient with fibular lon-
gitudinal deficiency, it is important to carefully examine the
contralateral extremity. It can be easy to miss a case of bilateral
deficiency when the deficiency on one side is mild. Make sure
not to focus on the more abnormal limb and to examine the
entire patient.
Complications
Amputation.
One of the major complications of the Syme
amputation is migration of the heel pad off the end of the
residual limb (Fig. 30-20). This is particularly true in con-
genital limb deficiencies, in which the heel may be on the
back of the tibia, making repositioning of the heel pad on the
end of the limb difficult or impossible. Heel pad migration
can be addressed with prosthetic modifications, but the con-
sequence is that it is no longer an end-bearing amputation.
Most other problems in patients with Syme amputation are
caused by other effects of the underlying disorder (90, 91,
109, 111).
With regard to the Boyd amputation, the main complica-
tion is the migration of the calcaneus if successful arthrodesis
is not achieved. Arthrodesis is difficult because both the dis-
tal tibial epiphysis and the calcaneus are largely cartilaginous
at the time of amputation. This can be addressed by remov-
ing the distal tibial epiphysis and fusing the calcaneus to the
distal tibial metaphysis, as mentioned previously. However,
if pseudarthrosis with calcaneal migration occurs, this can
require an additional surgery, which is often conversion to a
Syme amputation.
