Ankle Foot Orthosis

Fixed AFOs interfere with the child's ability to feel the floor through their feet and may interfere with performance of transitional movements, such as moving from sitting to standing.

Orthoses for the Muscle Disease Patient

Ankle–foot orthoses (AFOs) are used in two ways: first as an aid for ambulation, providing both support and assistance and allowing the patient to move through the various stages of gait. The AFO can be articulated at the ankle with various types of ankle joints that will limit or assist dorsiflexion and plantarflexion as needed. Alternatively the AFO can have a solid ankle with no ankle joint (Fig. 32.1). Currently, most of these orthoses are thermoformed plastic to allow for corrections for any type of ankle deformity. With the ability to adjust ankle position (dorsi- and plantarflexion) you also have the ability to control the knee position through ground reaction forces during the stance phase of the gait cycle (Fig. 32.2). In a second capacity, AFOs are used as night splints to prevent contractures. These are normally plantarflexion contractures with some ankle varus. When AFOs are used throughout the day and night and when they are provided early in the disease process, the person's ability to ambulate can be prolonged.

Neuropathic Ulcers ORTHOSES

An ankle-foot orthosis (AFO) may be indicated for a patient with peripheral motor neuropathy sufficient to cause foot drop. ROM and structure of the foot and ankle are assessed for fitting. The typical off-the-shelf AFO is usually fixed with a 90-degree bend at the ankle, assuming that the patient can achieve a neutral ankle position. If the patient has musculoskeletal impairments or swelling that prohibit dorsiflexion of the ankle to neutral, the AFO may not fit well, and if the patient also has peripheral sensory neuropathy, insults to the foot and ankle caused by the AFO may not be perceived. The outcome of a poorly fitted AFO may be breakdown of the skin with resulting wounds. AFOs with adjustable ankle hinges are available for the plantarflexed foot.

Ankle–Foot Orthosis–Footwear Combination Tuning

AFO–footwear combination (AFO-FC) tuning is becoming widely recognized as a means for optimizing the alignment of GRFs, with respect to joint rotation centers, to enhance normalization of the joint kinematics and kinetics. The process of AFO-FC tuning can be accomplished objectively or subjectively depending on the technology available to the orthotic practitioner (i.e., three-dimensional gait analysis, video vector systems, or basic clinical observation and patient feedback). However, many orthotists have not yet incorporated this tool into their daily clinical practice.

A cross-sectional survey of registered orthotists in the United Kingdom identified that only 50% of participants use AFO-FC tuning as standard clinical practice and that there exists a lack of understanding regarding the key principles of AFO-FC tuning among those that participated in the study.

A prerequisite for successful interventions and tuning of AFO-FCs is an optimal angle of the ankle in the AFO (AA-AFO). Common beliefs are that the AA-AFO must always be 90 degrees or that dorsiflexion and plantigrade positions are acceptable, but plantarflexion is not. Optimal AFO-FCs use a variety of AA-AFO, and the use of plantarflexion may be essential. In addition, a plantarflexed AA-AFO may increase musculotendinous unit length, facilitate knee extension in gait, allow the musculotendinous unit to be at the optimum length for force production, and prevent the development of bony foot deformities caused by enforced supination or pronation within the AFO.

Identifying and understanding the subtalar neutral position of the foot in an individual with CP is a key starting point to guide AFO footplate design, footplate length, and AA-AFO. An orthosis must effectively control ankle motion, maintain appropriate calcaneal and forefoot positioning, and have an AA-AFO equal to the maximum length of the gastrocnemius muscle. The combined effect of the heel–sole differential of the footwear coupled with the AA-AFO can be described as the shank-to-vertical-angle (SVA). The SVA (i.e., the tibia inclination) is the angle between the anterior surface of the tibia and the vertical angle in the global sagittal plane. Adjusting (i.e., tuning) the AFO-FC's properties could affect this alignment, which may be guided by monitoring the SVA.

It is important to note that the AA-AFO and the SVA are considered independent of one another. The ankle angle within the AFO is determined by muscle length, whereas SVA refers to the angle of the anterior tibia in relation to the vertical during the gait cycle. Tuning the AFO-FC will increase or decrease the SVA but will not alter the AA-AFO. Tuning focuses on manipulating segment kinematics, in particular tibial kinematics, to improve the relationship of the vertical GRF vector to the knee and hip during stance.

According to Owen, important kinematic characteristics at midstance (e.g., thigh inclination) can only be preserved with an SVA ranging from 7 to 15 degrees, whereas an SVA of 10 to 12 degrees of incline is suggested to be optimal and a good place to start. The SVA can be altered by the addition of small wedges between the AFO and the shoe. Additional alterations can be accomplished with external heel and sole build-ups that may also be tuned to optimize shank kinematic and GRF alignment by varying profiles and locations of heel and toe rockers.

More complex cases (e.g., severe crouch gait) present greater challenges, and significant footwear modifications may be necessary. In addition, other forms of intervention such as contracture reduction, botulinum toxin, or surgery may be necessary for successful tuning.

Cerebral Palsy Orthoses

 Ankle foot orthoses (AFOs) are routinely used in children with cerebral palsy to minimize development of calf muscle contractures, improve dynamic efficiency of gait, improve stance phase stability, and facilitate swing phase clearance. A systematic review of the effects of AFOs on gait found that studies of orthotic use have predominantly adopted a cross-sectional design, with generally poor-quality studies that lacked randomization procedures, were not blinded, and did not control patient attrition from the group. The review also noted confusing terminology for ankle–foot orthoses, with up to 12 different terms used. The authors were able to collapse these terms down into a small number of ankle–foot orthoses (hinged AFO, posterior leaf spring AFO, dynamic AFO, ground reaction AFO, and supra-malleolar orthoses). Although there are no reported effect sizes, the review noted that studies have generally agreed that gait velocity, step, and stride length and single-support time show a modest 5–10% increase with the use of AFOs when compared with barefoot walking. All AFOs, except supra-malleolar orthoses (SMOs), can improve ankle position during heelstrike either by decreasing ankle plantarflexion or by increasing dorsiflexion. They also reduce excessive equinus during mid-stance and can lead to increased dorsiflexion at terminal stance with better positioning of the ankle in the swing phase of gait. The fine-tuning of AFOs can also improve knee position in gait: AFOs set in ankle dorsiflexion act to reduce knee hyperextension and AFOs set in plantarflexion increase the plantarflexor knee extensor couple and reduce knee flexion. Radiographic studies have also shown small improvements in static foot alignment with the use of orthoses of children with cerebral palsy in the range of < 6°.

A useful guide to the clinical decision making on foot orthoses has been published by Davids et al. Their recommendation is that supra-malleolar orthoses have little to no indications for use in cerebral palsy. A quantitative gait analysis assessment of patients walking with supra-malleolar orthoses show no kinematic or kinetic improvements that could be attributed to the orthoses. The SMO is designed to treat excessive supination or pronation of the foot in patients without significant spasticity and, for this reason, could be expected to be relatively ineffective in controlling foot position in children with cerebral palsy. Posterior leaf spring orthoses (PLSO) are frequently used in cerebral palsy and are best suited for feet that have mild and passively correctable deformities, and relatively mild spasticity. They are designed to have contact with the plantar aspect of the foot with the posterior line extending to the proximal third of the calf. The posterior shell is narrowed from the distal tibial segment to the hindfoot allowing bending of the orthosis to accommodate ankle dorsiflexion in mid- to late-stance. Quantitative gait analysis studies have shown that posterior leaf spring orthoses reduce excessive ankle plantarflexion in swing phase while allowing ankle dorsiflexion in stance phase.

Hinged ankle–foot orthoses have a similar contour to that of the PLSO, but the posterior shell captures both the hindfoot and the posterior half of the calf. There is separation of the foot portion from the tibial portion and the two portions are connected by hinges, either metal or plastic. These orthoses also prevent excessive ankle plantarflexion in swing phase (foot drop), but allow ankle dorsiflexion in stance. Hinged AFOs can be either free or constructed to allow limited dorsiflexion. The primary contraindication to the hinged AFO is excessive ankle dorsiflexion in mid-stance during second rocker. This pattern of movement is commonly seen in older children with cerebral palsy, making this an unsuitable orthosis for the older child. It should also be noted that the hinged AFO is more labour-intensive and expensive to fabricate than the PLSO and more difficult to tolerate, owing to the thicker plastic and the hinges that necessitate greater modifications in the footwear.

Ground reaction AFOs (also termed floor reaction AFOs) are useful for control of crouch gait pattern but, in practice, are often difficult for children to tolerate unless spasticity in the hamstrings can be reduced either through intramuscular botulinum toxin A injections or through surgical means. These orthoses are, however, useful in the post-surgical phase where more support is required at the ankle and knee.

Orthotic use will probably change as the child grows and is influenced by the GMFCS level of the child. Young children (< 3 years) with little fixed contracture, but dynamic tone, often benefit from an off-the-shelf dynamic orthosis that can allow squatting and developmentally appropriate tasks. Several such orthotic designs are available and the reader is directed to company websites for further information (Cascade Orthotics 2013). Older children require more standard AFOs such as the posterior leaf spring; those with greater level of impairments (e.g. children who function at GMFCS level III or IV) often need greater orthotic support (e.g. solid AFOs or two-piece orthoses, incorporating a wrap-around inner shell and a stiff posterior outer frame to resist both dorsiflexion and block plantarflexion).

 Lower Limb Orthoses for Persons Who Have Had a Stroke

 Indirect Control of Knee Flexion
An AFO can provide indirect control of knee flexion. In this case the requirement is to block dorsiflexion and thereby manipulate the ground-reaction force (GRF) such that it passes in front of the knee center, creating an extension moment at the key unstable moment of stance when knee flexion would cause the knee to collapse. This principle was used in the design of the ground-reaction AFO, an AFO with the primary objective of controlling knee flexion by preventing ankle dorsiflexion while allowing the patient to lean into the anterior panel for stability in midstance, but it applies equally to any AFO used for this purpose. The angle at which dorsiflexion is blocked is critical and over the years has proved somewhat controversial. Although the original ground-reaction AFO design stipulated that the ankle must be held in a position of plantarflexion, this alignment causes difficulty with tibial progression in stance phase. Glancy and Lindseth concluded that the best gait pattern is achieved when the ankle is held in 5 degrees of dorsiflexion, and this alignment has become the modern ground-reaction AFO in use today. Ultimately, the alignment of the ankle joint is of considerable importance and is best determined for each patient individually. Double-adjustable metal ankle joints can be incorporated into the orthosis to allow for “fine-tuning” of ankle alignment. Optimization of the third rocker by footwear modification, such as the addition of a point rocker sole, can facilitate switching of the ground-reaction vector from extension to flexion in preswing.

Standing and walking with lower limb paralysis

Implications of an AFO on gait and gait-related activities

All types of ankle–foot orthoses, even a light leaf spring AFO for isolated paralysis of the dorsiflexor muscles, affect gait.

An AFO which blocks plantarflexion necessitates additional knee flexion at heel strike to get the foot flat on the ground. This requires large knee extensor torques to prevent knee collapse.The effect of an AFO on the knee at heel strike is exacerbated when walking up or down slopes. Placing an AFO in a less dorsiflexed position reduces knee flexion at heel strike. Occasionally the ankle joint is intentionally positioned in some plantarflexion (this type of AFO is called a floor reaction AFO). This helps stabilize the knee in extension and is used for patients with weakness of the quadriceps muscles.However, the more plantarflexed the ankle the more difficulty patients have with clearing the toes during swing.Foot clearance can be helped by a heel raise on the opposite side, although clearly bilateral heel raises will not alleviate a bilateral problem with foot clearance.

An AFO which blocks dorsiflexion has important implications for performance of gait-related tasks which rely on placing the foot in a fully dorsiflexed position. For example, moving from sit to stand relies on positioning the feet under the body with the ankles dorsiflexed. If the ankles are fixed at 90°, the only way to get the feet flat on the ground is by placing them further away from the body. This makes it difficult to get the centre of mass over the feet, a biomechanical prerequisite for standing up.Patients therefore need to push down through the hands to initially shift weight over the feet.

 Balance, Gait, and Falls - Assistive devices

 Ankle–foot orthoses are commonly used after stroke to stabilize the foot and ankle in stance, and lift the toes in swing. People with stroke score better on measures of walking independence and functional balance immediately after donning an ankle–foot orthosis. Stroke survivors also walk faster and stand more symmetrically while wearing, compared to not wearing, an ankle–foot orthosis. Stair negotiation time, Timed Up and Go time, and postural sway might also slightly improve with compared to without the ankle–foot orthosis.

Functional electric stimulation is an alternative approach to compensate for foot drop and lift the toes during swing. Both functional electric stimulation and ankle–foot orthoses seem to have similar effects in terms of improving walking speed in people with stroke. However, as the ankle–foot orthosis passively supports the ankle joint during mobility, longer-term wear may impair ability to activate the lower-leg muscles compared to using functional electric stimulation.

Gait aids, such as canes, walkers, or rollators, are often prescribed by physiotherapists for those with impaired balance and gait poststroke. Most studies examining the effect of gait aids poststroke have either compared habitual users of gait aids to those who do not use the aids, or have examined the immediate effect of using the aid on characteristics of gait and balance. People who ordinarily use a gait aid have worse balance and walk slower than those who do not.

Standing with a quad cane seems to improve quiet standing balance control, but does not improve standing symmetry, compared to a single-point cane or standing with no device, in people with subacute stroke. One study reported improved gait asymmetry when walking with a single-point cane compared to walking without a cane, whereas another study found no effect. Walking may be slowed immediately after providing a cane to people with subacute stroke who do not ordinarily use one for ambulation. People with subacute stroke who ordinarily use a cane have reduced gait variability and energy cost when walking with the cane compared to walking without it. However, those who do not usually walk with a cane have increased energy cost when walking with a cane than without. Studies comparing different kinds of gait aids found that walking speed and gait asymmetry and energy cost of walking are improved when using a single-point cane versus a quad cane. Furthermore, participants feel that the single-point cane is most beneficial, compared to a quad cane.

Overall, gait aids may help to improve stability after stroke, thereby promoting independence in walking and balance, but because there are no randomized trials it is difficult to know if improved function with the aid in habitual aid users is due to maladaptive behaviors and worsened performance without the aid.

 Ankle–Foot Orthoses Lower Limb Orthoses for Persons With Spinal Cord Injury

 AFOs are usually prescribed for individuals with ISCI or those with lesions between L4 and S2 to permit safe and effective ambulation by providing support for weakened musculature around the ankle joint, specifically to address the excess plantarflexion observed during initial contact, stabilize the joint for effective push-off during late stance, and prevent toe-drag during swing.3,94,105 The guiding principles for recommendation are to control the ankle joint by limiting excursion range, provide safe joint mechanics, prevent toe drag during the stance-to-swing transition, minimize the risk of falls, and enhance the ability to walk faster and more efficiently.

Lower Limb Orthoses - Common Ankle-Foot Orthosis Prescriptions

The most common AFO prescription for foot drop is a posterior leaf spring AFO, but for associated significant subtalar joint instability, a hinged plastic AFO with metal double-action ankle joints with springs in the posterior channels or a hinged, spring-loaded midline posterior stop AFO may be a better option.

For plantar spasticity, common prescriptions include either a hinged custom plastic AFO with a single midline posterior stop or a hinged custom plastic AFO with pins in the posterior channels to provide a plantar stop at 90 degrees. Permitting dorsiflexion allows a more normalized gait and provides a therapeutic stretch to the plantar flexors. Prefabricated carbon fiber AFOs are also available. The advantages of carbon fiber AFOs are lighter weight, lower profile footplate, and ability to provide some dynamic response or propulsion to substitute for weak plantar flexors.

For lumbar spinal cord injury, the typical AFO prescription is a bilateral custom plastic ground reaction (anterior tibial shell closing) AFO that is fixed in 10 degrees of plantar flexion. The plantar flexion creates knee extension moments with weight bearing to add stability to the knees during ambulation.

Orthotic Management of Neuropathic and Dysvascular Feet

Patellar-Tendon–Bearing Orthosis
An AFO can be modified to a patellar-tendon–bearing orthosis (PTBO) by adding an anterior band or formal anterior support to the existing AFO. Alternatively, the PTBO may suspend the foot and create a platform that is strapped to the leg and transfers weight from the pretibial region directly to the orthosis. Biomechanical studies show that the stress experienced by the foot is reduced on average by only 15% to 30%.Older studies have demonstrated some success with PTBO for talar avascular necrosis or Charcot arthropathy but note poor patient satisfaction with the brace.These designs are contraindicated in patients with vascular impairment related to potential popliteal vessel constriction by the tight anterior band. Given the propensity of skin ulceration and potential for vascular dysfunction in patients with neuropathy, these designs should be used with caution in this population.

 Lower Limb Orthoses - Common Ankle-Foot Orthosis Prescriptions 

The most common AFO prescription for foot drop is a posterior leaf spring AFO, but for associated significant subtalar joint instability, a hinged plastic AFO with metal double-action ankle joints with springs in the posterior channels or a hinged, spring-loaded midline posterior stop AFO may be a better option.

For plantar spasticity, common prescriptions include either a hinged custom plastic AFO with a single midline posterior stop or a hinged custom plastic AFO with pins in the posterior channels to provide a plantar stop at 90 degrees. Permitting dorsiflexion allows a more normalized gait and provides a therapeutic stretch to the plantar flexors. Prefabricated carbon fiber AFOs are also available. The advantages of carbon fiber AFOs are lighter weight, lower profile footplate, and ability to provide some dynamic response or propulsion to substitute for weak plantar flexors.

For lumbar spinal cord injury, the typical AFO prescription is a bilateral custom plastic ground reaction (anterior tibial shell closing) AFO that is fixed in 10 degrees of plantar flexion. The plantar flexion creates knee extension moments with weight bearing to add stability to the knees during ambulation.