A Review of
Thermoplastic Ankle-Foot Orthoses
Adjustments/Replacements in Young
Cerebral Palsy and
Spina Bifida Patients
Terry J. Supan, CPO
Christopher F. Hovorka, CO
ABSTRACT
A retrospective study was performed to
determine how long a thermoplastic ankle-foot orthosis (AFO) will fit appropriately and when subsequent adjustment and replacement are indicated.
Clinical records of cerebral palsy and
spina bifida patients ages birth to 21
years who used six types of thermoplastic AFOs from 1982 to 1992 were reviewed. Neuromusculoskeletal functional status appears to determine the
AFO design prescribed and its replacement. Adjustments to thermoplastic
AFOs primarily involve heat flaring to
alter plastic contours and provide sufficient space for donning, doffing and
pressure relief over regions of bony
prominence. Further research is necessary to confirm the results obtained in
this study.
Introduction
Within the field of orthotics, no known
published studies have addressed the
nature and frequency of adjustments
and subsequent replacement of orthoses prescribed for the lower limb. A
retrospective review was designed to
provide data to document the timing of
orthotic intervention in a neuromusculoskeletally maturing patient population. Numerous factors of thermoplastic ankle-foot orthosis (AFO) adjustment and replacement were derived
from the review of this data.
Methodology
A database was created using a spreadsheet on the Apple Macintosh computer. Medical files of 198 patients
wearing thermoplastic AFOs from
communities of central Illinois and
northeastern Missouri treated at
Southern Illinois University School of
Medicine, Orthotic/Prosthetic Services
(SIUO/P) between July 6, 1982, and
June 30, 1992, were recorded. Only patients diagnosed with cerebral palsy or
spina bifida between birth and 21 years
of age were chosen for this review for
two reasons. First, the majority of
lower-limb musculoskeletal growth
and development was completed by
the twenty-first year of life, which ensured a patient population undergoing
musculoskeletal growth without the
need for radiographic confirmation
(1,2). Second, patients diagnosed with
cerebral palsy or spina bifida were the
two most prevalent patient referral
groups for orthotic treatment of the
lower limb at this institution.
Thermoplastic AFOs were reviewed
since these orthoses were prescribed
frequently at SIUO/P over the 10-year
period for the two diagnosis groups,
which provided a considerable amount
of data for this review. The only exception was a modular thermoplastic
knee-ankle-foot orthosis (KAFO) incorporating separate AFO and removable thigh sections, which was used by
patients fully assembled for nocturnal
use and disassembled for AFO daytime
use (see Figure 1
).
Supramalleolar orthoses (SMOs)
with trimlines terminating within the
immediate region of the malleoli were
excluded from this study. No unique
contours (i.e., tone-reducing modifications) were incorporated into the
AFOs studied. Lower-limb orthotic
treatment objectives for both the cerebral palsy and spina bifida patients
treated in this review were similar. The
primary orthotic objective was to
achieve optimum foot and ankle joint
positioning to reduce or terminate progression of contractures and secondarily, when indicated, to provide for stable body weight transfers and safe ambulation.
Patient demographics were tabulated consisting of the patient's medical
record number, name, gender, date of
birth, diagnosis and treated limb.
Orthosis variables, such as the orthosis
type and dates of new adjustments and
replacements to patients' AFOs, were
recorded.
The type of orthosis was labeled and
classified according to the Health Care
Financing Administration (HCFA)
Common Procedure Coding System
devised by the American Orthotic and
Prosthetic Association in conjunction
with the American Medical Association (3). The frequency of regional adjustments to orthoses by heat flaring of
the thermoplastics was studied. Heat
flaring consisted of changing the shape
of the thermoplastic to reduce excess
pressure where it contacted the patient's limb. These adjustments were
performed during a clinic or office visit
and deemed appropriate when skin irritation was reported by the patient, his
or her family, or health-care workers
involved with the patient's care.
An adjustment legend was created
that divided the AFOs into 10 corresponding anatomical lower-leg sections
described by the corresponding bony
anatomy and its related soft tissues and
vessels (see Figure 2
). The foot section
of the AFOs was divided into four
quadrants. Section A, the medial forefoot, contained the first, second and
medial half of the third metatarsals and
phalanges. Section B, the lateral forefoot, contained the lateral half of the
third and the entire fourth and fifth
metatarsals and phalanges. Section C,
the medial rearfoot, contained the medial half of the calcaneous, medial half
of the talus, the navicular, the medial
cuneiform, the middle cuneiform and
the medial half of the lateral cuneiform. Section D, the lateral rearfoot,
contained the lateral half of the calcaneous and talus, the entire cuboid and
the lateral half of the lateral cuneiform.
The ankle section of the AFOs was
divided into medial and lateral halves
encompassing the malleoli. Section E,
the medial ankle, contained the medial
malleolus extending to the midline of
the distal leg anteriorly and posteriorly, and Section F, the lateral ankle,
contained the lateral malleolus extending to the distal leg's midline anteriorly
and posteriorly. The proximal two-thirds of the leg extending from proximal to the malleoli up to the knee was
known as the leg section and was divided
into four quadrants. Section G, the medial and anterior quadrant, extended
from the anterior midline encompassing
the medial two-thirds of the tibia.
Section H, the lateral and anterior
quadrant, extended from the anterior
midline to the lateral midline encompassing primarily the fibula. Section I,
the medial and posterior quadrant,
contained superficially a large part of
the medial gastrocnemius and soleus
tissue extending from the medial midline to the posterior midline. Section J,
the lateral and posterior quadrant,
contained the remaining lateral aspect
of the gastroenemius and soleus tissue
from the lateral midline to the posterior midline.
Only three of the six thermoplastic
orthoses (solid, floor-reaction and articulated AFOs) were reviewed according to the site of heat flare modifications performed because these devices were used predominantly among
the patient population. The other three
orthoses (articulated floor-reaction,
Thermoplastic Elastomer (TPE) and
dorsiflexion assist AFOs) were not
considered in this aspect of the study
because they were rarely heat flared
(4). The articulated floor-reaction
AFO was used only for a short time
during the study, and the other two
devices (TPE and dorsiflexion-assist
AFOs) were prescribed infrequently
with little or no documented heat flare
adjustments performed.
The replacement of thermoplastic
AFOs was recorded according to re-
placement criteria based on either a
physiologic change in the patient or
change in the structure of the AFO (see
Table 1
). All patients were treated with
an initial orthosis and as many as four
subsequent replacements for both the
cerebral palsy and spina bifida patient
groups.
ResultsPatient Distribution by Diagnosis
Of the 198 patients reviewed, there
were 112 males and 86 females. One
hundred sixty-seven of these patients
(84 percent) were diagnosed with one
of three spastic types of cerebral palsy:
diplegia (38 percent), hemiplegia (22
percent) or quadriplegia (19 percent)
(see Figure 3
). A small group (5 percent) of patients was diagnosed with a
variety of other types of cerebral palsy
and was categorized as miscellaneous
types. Thirty-one of the 198 patients
(16 percent) were diagnosed with spina
bifida, of which 30 patients were diagnosed with a myelomeningocele and
one patient with a meningocele (see
Figure 4
). Eighteen of the 31 spina bifida patients (58 percent) had their spinal cord defect within the lumbar level
followed in order by 23 percent unspecified (seven patients), 13 percent
sacral (four patients) and 6 percent
thoracic levels (two patients).
Distribution of Orthosis Type
Six types of thermoplastic AFOs were
used to treat the patients (see Figure
5
). A total of 254 devices were prescribed, 83 percent for patients with
cerebral palsy and 17 percent for those
with spina bifida. For patients with cerebral palsy, the solid AFO was pre-
scribed for the majority (58 percent)
followed by the articulated (26 percent), floor-reaction (9 percent), dorsiflexion-assist (4 percent), articulated
floor-reaction (2 percent) and TPE (1
percent) devices (see Figure 6
).
Patients with spastic quadriplegia
usually were treated with a solid AFO
while those with spastic diplegia or
hemiplegia were usually treated with
either a solid or articulated AFO. All
other types of cerebral palsy were
treated less frequently and with other
types of devices.
The remaining 17 percent or 43
AFOs were prescribed for patients
with spina bifida. Within this group, 44
percent were treated with the floor-reaction AFO, followed by the solid (42
percent), articulated floor-reaction (12
percent) and dorsiflexion-assist (2 percent) devices. The majority (58 percent) of the spina bifida patients were
ambulatory, with their neural tube defect within the lumbar regions (see Figure 7
).
Replacement Timelines
The number of patients treated with
replacement orthoses reduced considerably with each successive AFO replacement. In addition, there was a
wide range in age for the group of patients fit with an initial AFO, which
reduced tremendously with each subsequent replacement (see Figure 8a
, Figure 8b
, Figure 8c
, and Figure 8d
).
Beyond the usual reasons (surgery,
transfer of care, etc.), patients underwent subsequent replacement of orthoses for one of two causes. First, the
older children no longer required replacement orthoses due to the lack of
growth, or the patient's existing orthoses were discontinued. Second, the
younger patients did not require as
many replacement orthoses since they
had not yet outgrown their existing
orthosis. This had a greater effect on
the data of the female patients than on
those of the male patients. The group
mean age of female patients actually
declined from the first to the second
replacement orthosis (see Figure 8b
and Figure 8d
). In all groups, males were older than their female counterparts except for females with spina bifida who
were older at their third and fourth
AFO replacements. Overall, males
with cerebral palsy had their orthoses
replaced an average of 0.9-year (10.8
months) intervals while those with
spina bifida had theirs replaced an average of 1.51-year intervals.
Distribution of Adjustments Performed
to Orthoses by Patient Diagnosis and
Type of Device
The reporting of heat flare adjustments
by anatomic location was the single
most common recorded modification
to a thermoplastic AFO over the 10year review. The three types of AFOs
used by patients diagnosed with cerebral palsy (solid, floor-reaction and articulated) and those patients diagnosed
with spina bifida using the solid or
floor-reaction AFOs displayed many
differences in the frequency of adjustments performed (see Figure 9a
, Figure 9b
, and Figure 9c
).
Solid and articulated AFOs were
most often adjusted at the foot, ankle
and proximal leg. Most adjustments
were performed at the foot's navicular
region except for spina bifida patients.
The fewest adjustments were performed at the proximal leg region. Patients using the floor-reaction AFO
had the greatest number of adjustments at the proximal leg and fewest
adjustments at the foot and ankle. The
floor-reaction AFO had more combined adjustments in the calf of the
proximal leg and the fewest adjustments at the ankle.
DiscussionDistribution of Orthosis Type by
Patient Diagnosis
When this distribution is compared to
the neuromusculoskeletal function of
those patients with cerebral palsy,
some generalizations may be made.
Patients, such as the spastic quadriplegic group, required control of the foot,
ankle and knee offered by the solid
AFO or modular thermoplastic KAFO
with removable thigh shell. These individuals, most of whom were nonambulatory, were prescribed those de
vices for prevention of joint contracture or lower-limb joint stabilization
during transfers (e.g., from wheelchair
to bed).
The spastic diplegic and hemiplegic
groups generally displaying less neuromusculoskeletal involvement of the
limbs were prescribed additional types
of orthoses. Patients with spastic hemiplegia were fitted with either a solid or
articulated AFO for select motion control about the foot, ankle and knee
when ambulation was achieved. Patients with spastic diplegia used the
greatest variety of devices.
In addition to the solid and articulated AFOs, a small number of the spastic
diplegic patients were prescribed floor-reaction and articulated floor-reaction
devices, the latter intended to control
excessive ankle dorsiflexion and
crouch during ambulation. The articulated floor-reaction AFO introduced in
the 1980s concurrently by Beverly Cusick, MS, PT (described as a hinged
crouch-control ankle-foot splint) and
Algis Maciunas, CPO, in conjunction
with James Gage, MD, (described as a
rear-entry hinged floor-reaction AFO)
recently was introduced at SIUO/P and
used during the last 10 months of this
study (5,6).
This distribution of orthosis type by
patient diagnosis also relates the spina
bifida patient's functional status to
type of orthosis prescribed. Because
spina bifida typically presents with paralysis at and below the level of neural
tube defect, those patients with high
levels of pathology (superior to the
lumbar level) were prescribed solid or
floor-reaction devices while patients
retaining greater distributions of muscular function through lower levels of
spinal cord involvement used the articulated floor-reaction device. The entire spina bifida group with the exception of one dorsiflexion-assist AFO
prescribed for a patient with a low-level myelomeningocele displayed the
importance of crouch control offered
by the two variations of floor-reaction
devices.
In effect, the spina bifida group was
treated for foot and ankle control in
addition to control of knee buckling
secondary to weak-knee extensors associated with the level of their pathology. The cerebral palsy group was treated for foot, ankle and knee control depending on each person's level of upper motor neuron pathology. This distribution comparison supported the
principle that the orthosis prescription
was related to the patient's functional
needs based on the level of his or her
neuromusculoskeletal involvement.
Replacements
The dwindling size of the patient populations when treated with subsequent
replacement orthoses was due to several factors. Fewer older patients required replacements due to discontinuance of the orthosis or reduced rate of
growth. The patient's moving from the
area, surgical intervention performed
for contracture (tendon and/or muscle
transfer or lengthening), spasticity
(dorsal rhizotomy), joint instability
(arthrodesis), nutritional status or
change of referring physician and/or
the orthotist also may have contributed
to this effect.
Distribution of Adjustments
Overall, adjustments to orthoses were
performed for multiple reasons, including limb growth, biomechanical
changes secondary to surgical procedures and progression of deformities
such as joint contractures or other
neuromusculoskeletal change. By corresponding anatomical site, heat flaring modifications in the proximal calf
region of floor-reaction AFOs were
performed to allow adequate malleoli
clearance for donning and doffing.
This procedure modified the existing
orthosis design so the foot and ankle
could pass through the proximal posterior section. Fewer adjustments were
performed in the proximal leg region of
solid and articulated AFOs than other
sites since the gastrocnemius and soleus tissues in this region are more accommodating for donning and doffing.
The similarity of adjustments within
the foot section points to the importance of providing adequate relief of
bony prominences, particularly at the
medial posterior region where the navicular tuberosity resides. This condition may be related to the great range
of motion through which the medial
longitudinal arch of the foot moves
during weightbearing in conjunction
with positional changes during musculoskeletal growth and development. In
the ankle region, adjustments were
performed to provide adequate clearance of the malleoli with varying distributions for each of the three devices.
Conclusion
Through a 10-year retrospective to determine how long a thermoplastic AFO
will last and when it requires adjustment and replacement, this study exhibited a host of factors involved. The
main variable determining type of
orthosis prescribed appears to relate to
the patient's neuromusculoskeletal
functional status. Replacement of
AFOs was related to the patient's neuromusculoskeletal functional status and
possibly the gender, but the latter
could not be determined in this study.
The anatomical site of adjustments involving heat flaring depends largely on
the type of orthosis and the patient's
anatomy. Adjustments were made to
provide sufficient space for donning
and doffing in addition to providing relief of the patient's bony prominences
and skin pressure tolerance.
A typical scenario of orthotic intervention as gleaned from this study may
be that a patient with spastic cerebral
palsy usually required a solid or articulated AFO, necessitated adjustment
mostly at the medial rearfoot section at
the navicular followed by adjustments
at the ankle and anterior leg sections
within the proximal third, with average
replacement in 10.8 months. A patient
with spina bifida and a neural tube defect in the lumbar region may be prescribed a floor-reaction or solid AFO.
The floor-reaction device required
most adjustment in the posterior calf
section at the proximal third followed
by the medial rearfoot section at the
navicular and least adjustment in the
ankle section. The solid ankle device
required adjustment mostly in the medial rearfoot section at the navicular
followed by the ankle and anterior leg
section at the proximal third. Both the
solid ankle and floor-reaction AFOs
worn by patients with spina bifida average replacement in 1.51 years.
Since this retrospective study considered only some of the many factors involved in lower-limb thermoplastic
AFO treatment patterns for a neuromusculoskeletally maturing patient
population, further research would be
needed to evaluate the results obtained.
A copy of the AFO adjustments and
replacements spreadsheet format is
available upon request by contacting
Christopher F. Hovorka, CO, Newington Orthotic and Prosthetic Systems,
Children's Hospital Center, 181 E. Cedar St., Newington, CT 06111.
Acknowledgements
The authors thank Stephen Hill for his review of the manuscript.
TERRY J. SUPAN, CPO, is director of Orthotic/Prosthetic Services and associate professor of the Division of Orthopaedics and Rehabilitation, Department of Surgery, Southern Illinois University School of Medicine, P.O. Box 19230, Springfield, IL 62794-9230.
CHRISTOPHER F. HOVORKA, CO, was an orthotic resident at Orthotic/Prosthetic Services Southern Illinois University School of Medicine during the time this study was conducted and is a staff orthotist/prosthetist at Newington Orthotic and Prosthetic Systems, Children's Hospital Center, 181 E. Cedar St., Newington, CT 06111.
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