A paradigm shift is underway, whereby ankle equinus deformity in
children is managed with three important factors in mind: 1) as a component of
a sensory deficit associated with problems of postural control; 2) as a
biomechanical element in single-limb stance whereby the rate of tibial
inclination is more significant than the ankle angle; and 3) in acknowledgement
of the necessity to protect foot joint alignment from deforming strains imposed
by weight-loaded tension from a calf muscle contracture.
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| The components of the new paradigm concept for AFOs includes a foot orthosis insert to protect alignment. |
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| Images: Beverly Cusick |
Within the new paradigm, ankle foot orthoses (AFOs) are made to align
the foot joints for optimum weight loading first, and to accommodate a
gastrocnemius muscle contracture while limiting early or excessive ankle
dorsiflexion (DF), as is seen in crouch posture. Premature tibial inclination
has gained attention, as opposed to limiting ankle plantarflexion (PF). The new
paradigm is exemplified in the principles and methods employed in the
specialized design of below-knee serial casts used for postural and gait
training and in the “tuning” of solid AFOs and foot wear
combinations.
Maintain verticality
All living beings are driven to achieve and maintain the upright
position, beginning in early infancy. The most basic mechanism for maintaining
verticality is a righting reaction which involves the recruitment of the
muscles on the side opposite a body sway. The somatosensory receptors –
proprioceptors, mechanoreceptors and pressure receptors in muscles, connective
tissue, joints, and skin – have direct links to the muscles along the
spine as well as to the cerebellum and the sensorimotor cortex. Despite having
an abundance of ankle DF range of motion (ROM), typically developing infants,
while standing and walking, load the whole foot, but because they have not
mastered the use of the antigravity flexors on the front of the body for
balance they tend to carry more body weight on the midfoot and forefoot than
the heel. In this way, they can rely on the more primitive and usually better
developed extensor muscles on the dorsal trunk and limbs to remain upright. The
weight-loading pattern matures, moving rapidly toward the heel, within 6 months
of walking. By age 4 to 5 years, developing children with well-aligned feet can
be expected to distribute 60% of body onto the heels and 35% onto the
metatarsal heads. This load distribution remains into adulthood.
Master control
Research on motor learning shows the magnitude of practice involved in
the process of learning to manage body weight over the feet subconsciously
while engaged in play. The somatosensory receptors in the feet and ankles
deliver vital information to the cerebellum and sensorimotor cortex that is
used in the process.
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| Proper intervention for equinus deformity involves aligning the foot joints for optimum weight loading. |
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A typically developing infant who is not yet walking unsupported can
practice shifting body weight onto and off of each foot more than 1,000 times
per waking hour, for hundreds of hours, before attempting to take his or her
first steps. The infant begins to master control of his or her body center of
mass (COM) — both in space, and in relation to his or her feet —
while gaining muscle strength to carry body weight on one foot at a time and
then while in motion. This fundamental skill can take as long as 10 years to
master fully.
In children with diplegic cerebral palsy (CP), the equinus gait
han to decelerate the tibia in midstance and contribute to propulsion. As long
as the foot is aligned in pronation, the body COM is drawn forward and medially
on the feet by virtue of the pronatory motions of the calcaneus and talus. Soft
tissue stiffness and contractures of the posterior and lateral leg compartment
musculature emerge over time via physiologic adaptation to the prolonged,
tonic, use history.
Comparative analysis
In a landmark gait study by Sisson et al in 1994, gait analysis and EMG
were used to record the activation of the medial gastrocnemius (MG) muscle
belly in two 10-year-old boys – one with diplegia and one without
diplegia. Each child walked with his body COM displaced anteriorly, and again
aligned more optimally. Both participants showed a tonic MG activation while
walking with weight line forward – such that the nondisabled boy might be
deemed spastic by the look of his EMG record – and both showed a
significant normalization of the activation pattern when walking with weight
line more posterior. The boy with diplegia showed evidence of continued tonic
– though diminished – recruitment of the MG with weight line back,
but he also showed evidence of an emerging propulsion power burst.
A major objective of revising the design of an AFO according to the new
paradigm is to retrain the child to move his or her body weight back to a more
normal and efficient orientation over the feet, and in so doing, to:
- deliver more normal and appropriate somatosensory input to the heels
and load-bearing limb joints; - relieve the triceps surae, toe flexors, and other dorsal muscles of
antigravity righting and balancing work; and - allow the posterior compartment muscles to relax and lengthen via
physiologic adaptation to the new history of use that featuresthe presence of a
more efficient postural alignment.
In an effort to determine the optimum candidates for effective tuning of
AFOs and footwear, in 2007 Penelope Butler et al, undertook a retrospective
review using video records of 21 independently walking children with CP. Using
real-time force vector and other forms of computerized gait analysis, all 21
children showed a ground reaction force vector (GRV) in front of the knee
during midstance when barefoot – they hyperextended the stance knee.
The effectiveness of AFO tuning was judged by optimization of the GRV at
the knee, and showed that there were two groups of prospective candidates based
on knee kinematics. Those who optimized the GRV showed knee flexion less than
or equal to 20° in the first third of stance combined with movement towards
knee extension in the second third of stance that brought the knee to less than
or equal to 10° degrees flexion. So, as is usually the case, the children
with milder postural and movement problems showed better tuning effects than
those with more significant kinematic deviations.
Improper treatment
In light of new information, equinus deformity has been mistreated for
as long as it has been treated at all. In my experience, and with few
exceptions, orthotists fill prescriptions from physicians for either solid or
articulated AFOs that block the ankle from plantarflexing past 0°,
presumably because they think that ankle PF is the problem.
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| Improper treatment for equinus deformity involves blocking the ankle from plantarflexing past 0. |
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Children with shortened gastrocnemius muscles are usually molded for
AFOs while sitting with the knees flexed and the gastrocnemius muscle off
tension. Then, wearing the AFOs that prevent PF, the child steps onto a
battlefield. Since the gastrocnemius is a competent knee flexor, short gastrocs
impede knee extension when the ankle is held at 0°. Efforts to stand
straight raise the heel in the AFO, which is built to resist just that. The
foot joints take the DF strain and usually pronate within the AFO. Foot
pronation brings – and keeps – the body COM forward anatomically and
biomechanically. Boney prominences rub against the plastic at the medial
midfoot and lateral forefoot. No one is happy – not the child, the
caretaker, the therapist, or the orthotist. Requests to revise the AFOs to
improve comfort are difficult to satisfy with the ankle limited to 0° PF.
AFOs that block ankle PF and impose foot pronation can cause additional
problems because they impede functional use of the feet and ankles, provoking
therapists to remove them during treatment sessions. If they limit optimum
function or hurt, the children might refuse to wear them, or complain enough
that caretakers remove them right after school.
A more effective orthotic strategy
Children with equinus deformity must learn to carry their body weight
less anteriorly. Designing an AFO to allow some degree of PF is appropriate as
long as the heels are taking more weight than the metatarsal heads in the
standing position and in the early stance phases of gait. If the ankle must be
positioned in greater than 10° PF in the AFO, it is preferable to prepare
the ankle and foot first with a short course of serial casting in which the
foot ankle angle, the shaft angle to the floor, and the plantar surface of the
cast are all designed (“tuned”) for optimum weight loading through
the foot. If serial casting is not possible, then the sole of the shoe that is
worn with a tuned AFO set in greater than 10° PF should be made stiff at
the toe end, and if possible, longer than normal, to resist early anterior
carriage of the body COM over a foot that has been effectively made too short
by the ankle plantarflexed position.
Setting the foot joints in stable alignment, the ankle with a shortened
gastrocnemius muscle in PF in an AFO, and filling the space under the heel with
a lift, improves the likelihood that the heel will be weight-loaded easily and
often, providing the foot with more normal proprioceptive input. Using an AFO
with the ankle set in PF will not increase equinus deformity if the orthoses
are used to support a postural retraining program designed to reduce day-long,
tonic calf muscle recruitment for balance. If body weight is better aligned
over the heels, the calf musculature – no longer needed primarily for
balance against falling forward – can recover a healthier length and
extensibility. The significant improvements in ankle DFROM due to serial
casting, undertaken as described above, are evidence of the potential influence
on DFROM of proper AFO and footwear tuning combined with weight-line
distribution and weight–shift training.
The time has come to regroup, to review the news about the somatosensory
system, the postural control mechanisms, and the influence of standing foot
position on body weight orientation over the feet, and to forge a new and more
effective orthotic strategy – one that normalizes weight loading through
the feet, particularly the heels – and promotes the acquisition of balance
control as a background function that supports effective movement.
For more information:
Adolph KE, Avolio AM, Barrett T, Mathur P, Murray A. Step counter:
quantifying infant’s everyday walking experience. Infant Behavior
& Development. 1998. 21: 43.Aharonson Z, Voloshin A, Steinbach TV, Brull MA, Farine I. Normal
foot–ground pressure pattern in children. Clin Orthop Relat Res.
1980; 150: 220-223.Bertsch C, Unger H, Winkelmann W, Rosenbaum D. Evaluation of early
walking patterns from plantar pressure distribution measurements. First year
results of 42 children. Gait Posture. 2004;19(3): 235-242.Butler PB, Farmer SE, Stewart C, Jones PW, Forward M. 2007. The
effect of fixed ankle foot orthoses in children with cerebral palsy.
Disabil Rehabil Assist Technol. 2007;2(1): 51-58.Cavanagh PR, Rodgers MM, Iiboshi A. Pressure distribution under
symptom-free feet during barefoot standing. Foot Ankle. 1987;
7(5): 262-276.Cusick B. Serial Casting and Other Equinus Deformity Management
Strategies for Children & Adults with CNS Dysfunction. Telluride, CO:
Progressive GaitWays, 2010. Available at: www.gaitways.comGrant-Beuttler M, Palisano RJ, Miller DP, et al. 2009.
Gastrocnemius-soleus muscle tendon unit changes over the first 12 weeks of
adjusted age in infants born preterm. Phys Ther.
2009;89(2):136-148.Hennig EM, Rosenbaum D. Pressure distribution patterns under the
feet of children incomparison with adults. Foot Ankle.
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kinematics especially when using ankle-foot orthoses. Prosth Orthot
Int’l. 2010; 34(3):254-269. Available at:
http://poi.sagepub.com/content/34/3/254.full.pdfOwen E. The importance of being earnest about shank and thigh
kinematics especially when using ankle-foot orthoses. Prosth Orthot
Int’l. 2010; 34(3):254-269. Available at:
http://poi.sagepub.com/content/34/3/254.full.pdfSisson GA Jr, Weck M, Prihoda W, et al. The effect on gait of an
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http://symposiet.files.wordpress.com/2010/05/bowers-presentation.pdf
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