Impression Techniques and
Model Modification of a
Custom-Molded Ankle-Foot
Orthosis for the Idiopathic
Clubfoot.
James N. Athearn, CO
Justina S. Case, CO
John M. Roberts, MD
ABSTRACT
With careful impression techniques and
model modification methods, a custom
ankle-foot orthosis (AFO) may be fabricated to meet the requirements of a
physician prescribing noninvasive treatment for postsurgical clubfoot care. The
impression is obtained with maximum
achievable correction and modified using three-point pressure systems that
overcorrect the clubfoot deformity.
This AFO, in the experience of the authors, is effective in protecting the surgical corrections from undue stresses early on as well as helping to prevent postoperative recurrence of the deformity.
The postoperative time in a cast also
may be shortened if proper orthotic
treatment is achieved. Some advantages
of a shorter cast period include convenience for patient and family and less
risk of skin breakdown.
Introduction
Congenital clubfoot is a deformity noted at birth that includes both idiopathic and nonidiopathic clubfeet (1). The
deformity has been found to occur in
one to three cases per 1,000 live births
(1-3) with a ratio of 2.5 males to 1 female (1).
Although the causes of clubfoot are
generally thought to be multifactorial,
it has been suggested the uterine environment may interfere with normal
embryologic development in these patients (3,4). Other possibilities include a
lesion of the peroneal or tibial nerve
systems, heredity, bone anomalies and
subluxation of the talo-navicular joint
(1-4).
More recent information seems to
indicate arrested development of the
limb in early fetal life results in clubfoot (5-7). The normal fetus passes
through a stage of "physiologic clubfoot" during the ninth intrauterine
week (8). Factors that indicate a possible arrest in development at this stage
include a high rate of associated arterial dysgenesis; the discovery of myofibroblasts, postnatally, on the posterior
and medial aspects of the clubfoot; and
the diagnosis by ultrasound of the
deformity in utero as early as 13 weeks
(5-7).
In the idiopathic clubfoot, the foot is
the only deformity; the musculoskeletal
system is otherwise normal (1,3). The
nonidiopathic clubfoot may be present
at birth as a local manifestation of other neuromuscular disorders such as
arthrogryposis, Larsen's Syndrome, diastrophic dwarfism, myelomeningocele
and muscular dystrophy (1-3,9,10). The
deformity also may become apparent
after birth in pathologies such as cerebral palsy, spina bifida and hydro
cephalus (1). The clubfoot deformity
seen in association with arthrogryposis,
myelomeningocele, muscular dystrophy and other neuropathic diseases
tends to be more resistant to treatment
even though its cause is understood
(1,2). This may be due to muscular imbalances and ligamentous hypertrophy
(1,2,4).
A diagnosis of clubfoot can be described as talipes equinovarus. This can
be divided into four main deformities:
- short medial column (adduction
and cavus of the foot)
- hindfoot supination (varus)
- equinus
- medial spin (medial transverse rotation of the foot relative to the shin)
with lateralization of heel
Treatment for any kind of clubfoot is
started as soon as possible after birth
(2,4,11). The goal of treatment is to obtain a lasting correction and a foot that
is functional and cosmetically accept
able (1). Treatment goals also should
include making the maximum attempt
to maintain normalcy in the lives of the
patient and the patient's family (1).
There are many methods of treatment (1,2,4,11,12). The following methods are used at the Shriners Hospital
Springfield Unit, where 419 patients
with idiopathic clubfoot were under
treatment at the time of this study.
Shortly after birth, treatment with serial manipulations and plaster casting is
begun. The patient is evaluated after
undergoing three months of weekly
cast changes with more correction attempted at each cast change.
If a foot seems to correct rapidly, it is
probably a nonstructural clubfoot. An
ankle-foot orthosis (AFO) is fabricated
during the final two weeks of casting
and is fit and delivered when the final
holding cast is removed. It is worn for
12 out of 24 hours for three to six
months with convenience to the family
dictating which hours of the day or
night it is worn. A Denis-Browne
splint for night wear may be indicated
to treat persistent medial spin. Follow-up continues on an as-needed basis for
at least five to 10 years.
If correction of adduction and
supination proceeds rapidly, but the
heel remains high and a midfoot breach
occurs, a complete posterior release
may be indicated. If more than one element of deformity persists after three
months of casting, more comprehensive
surgery is performed. Postoperative
casting continues for at least two
months after surgery, followed by application of an AFO.
Postoperatively the foot is placed in
an "0" splint, in which it is held in the
corrected position with the knee flexed
to 90 degrees. The foot and leg are first
wrapped with Webril Undercast
Padding. Plaster bandage is wrapped
around the foot and continued up the
medial and lateral sides of the leg and
over the knee in a fashion similar to
"Robert Jones strapping" as described
by Lehman (2). The Webril then is split
anteriorly from knee to toes to allow
for swelling, and the entire splint is
re-wrapped with Kling to hold it in
place.
At one week, the splint is removed,
the wound is inspected, dressings are
applied and a definitive full leg cast is
applied. If complete correction is not
obtained at this time, serial casting ma
be indicated. Postoperative casting continues for two months, and an impression for an AFO is obtained at fly
weeks. The AFO is fit and delivered a
the time of removal of the final cast
Again, if medial spin persists, a Denis
Browne splint may be used in conjunction with the AFO.
Methods
One orthosis that is commonly prescribed and fabricated at the Shriners'
Hospital as part of both the noninvasive regime and postoperative treatment of the clubfoot is a custom-mold
ed AFO with corrective forces based
on three-point pressure systems aimed
at specific clubfoot deformities (see
Figure la
and Figure 1b
). The AFO is fabricated from 4-mm (5/32-inch) or 4.8-mm
(/6-inch) polypropylene, depending on
the size of the child, with a 4.8-mm (3/16inch) Pelite varus prevention pad
placed just proximal to the lateral
malleolus. It is delivered with Velcro
pretibial and ankle straps. The ankle
strap may be extended over the dorsum
of the foot medially to prevent the
great toe from overriding the medial
wall. The AFO may be worn at night in
conjunction with a Tibial Torsion Transformer or a Denis-Browne bar for
treatment of persistent medial spin.
The impression technique for this orthosis is of utmost importance. Maximum correction is desired. Molding
with plaster bandage or a synthetic material such as Scotchcast' is acceptable,
and landmarks should be outlined.
The impression position should be as
follows: If the left foot is being molded,
the practitioner's right hand should be
holding the calcaneus in a neutral position while pressing the thumb proximal
to the lateral malleolus to produce a
medially directed force to prevent
varus at the ankle. The index finger
should create a depression proximal to
the insertion of the Achilles tendon to
the calcaneus. This will create a pocket
in the impression for the heel, which
will transfer to the AFO and help prevent the heel from rising into an equinus position relative to the forefoot.
The practitioner's left hand should be
pushing the forefoot into as much abduction as possible while maintaining
the ankle at 90 degrees, and the forefoot should be at a neutral position of
pronation/supination.
Model modifications are based on
three-point pressure systems for maximum overcorrection. One three-point
pressure system consists of a varus prevention pad above the lateral malleolus, the medial border of the foot, and
the proximo-medial area of the calf
(see Figure 2
). This three-point pressure system acts on the ankle joint and
the subtalar joint to prevent or block
varus. The modification of the varus
prevention pad is accomplished by removing approximately 3 mm (1/8-inch)
of plaster from the model at the position of the thumbprint left from the impression procedure proximal to the lateral malleolus. Wrapping the excavation anteriorly (toward the tibial crest)
will result in a varus pad that will reduce the tendency of the AFO to rotate
medially around the leg; otherwise medial spin will not be controlled.
A second three-point pressure system (see Figure 3
) consists of two
forces directed laterally-one in the
area of the first metatarsal head, the
other at the medial side of the calcaneus-and a medially directed counterforce just proximal to the base of the
fifth metatarsal and cuboid. This three-point pressure system increases the
length of the medial column through
the midtarsal, talo-navicular and calcaneo-cuboid joint(s). This is achieved
through plaster removal at the medial
forefoot of the model. Beginning at the
space between the second and third
digits, plaster is removed to a point just
proximal to the metatarsal heads (essentially removing the first two toes)
(see Figure 4a
).This places the forefoot
and midfoot in an abducted position in
the AFO, which is fabricated with a
high medial wall. This overcorrection
should be maximal (to the extent tolerable by the patient). The tendency is
that the younger the child, the more
overcorrection possible. Plaster removal to the third digit is appropriate
on an infant. The 5-year-old, on the other hand, may tolerate plaster removal
only partially through the first digit.
Approximately 3 mm (1/8-inch) of
plaster also must be removed from the
model at the medial border proximal to
the first metatarsal head to provide relief for the metatarsal head. The plaster
removal on the medial side must be
compensated for on the lateral side by
the addition of an amount of plaster
equal to that removed (see Figure 4b
).
Plaster buildups also are added over
the malleoli for the older child. The infant normally has enough extra tissue
that buildups produce only a sloppy fit.
Addition of plaster over the heel is
avoided to maintain good calcaneal
control in the neutral position.
The third three-point pressure system employed maintains the foot at a
90-degree angle to the shin (see Figure
5
). This three-point pressure system
works through the ankle joint to resist
equinus. This is the standard force system seen in most AFOs, which directs
one upward force at the plantar aspect
of the metatarsal heads, another anteriorly directed force at the proximal-posterior calf and a third obliquely directed force at the instep (provided by an
ankle strap and/or shoe laces).
The toe plate is extended to encompass the full plantar surface of the foot
to ensure the medial wall of the footplate will extend to the end of the toes;
this provides the pressure for the overcorrected, abducted position in which
the foot is held.
Once the plaster buildups are added
and plaster removal is completed, the
model is checked to be sure the hindfoot (subtalar joint) is in a neutral inversion/eversion position, the ankle
joint is at 90 degrees, and the medial
column is lengthened. The model is
then smoothed, the trim lines are
drawn and the cast is prepared for plastic vacuum-forming with the Pelite
varus prevention pad in place over the
aforementioned excavation.
Complications
Complications in performing this procedure have included slippage of the
AFO distally due to recurrent equinus/heel rise, skin rash and/or breakdown, and shoe-fitting problems.
Slippage has been addressed with the
addition of a molded anterior tongue of
1.5-mm (1/16-inch) polyethylene , extending proximally from the top of the
varus prevention pad distally to the
dorsum of the midfoot. This may be
used in conjunction with a 3.2-mm (1/8k
inch) Thermofoam pad adhered to the
inside of the AFO in the area of the
Achilles tendon. Skin rash and breakdown is most often caused by the 23- to
24-hour per day wear of a plastic orthosis. This problem has been alleviated by
instructing parents to dress their children in white cotton socks and to
change them frequently. A ventilation
or "weep" hole may be placed in the
posterior-distal area of the calcaneus.
To prevent problems of shoe fit, soft
Blucher-type sneakers with the innersole(s) removed are recommended.
Conclusion
The authors have found the impression
procedures and model modification
techniques described herein have been
effective in producing an orthosis that
maintains the correction of clubfoot
deformities that have been effected
through manipulation, serial casting
and/or surgery. The described AFO has
been acceptable to the physician, the
patient and the patient's family for preventing recurrence of the clubfoot deformity. The modifications address all
aspects of the deformity: shortened medial column, hindfoot supination, equinus and medial spin. The method described herein is recommended as an
option for the treatment of clubfoot.
JAMES N ATHEARN, CO, is assistant director of orthotics at Shriners Hospital for
Crippled Children, 516 Carew St., Springfield, MA 01104.
JUSTINA S. CASE, CO, was a staff orthotist at Shriners Hospital, Springfield,
Mass., during the research and writing of
this paper, and is currently employed as a
staff orthotist at CEL. Prosthetics and Orthotics, 43 N. Cleveland, Memphis, TN
38104.
JOHN M. ROBERTS, MD, is chief of
staff at Shriners Hospital, Springfield, Mass.
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