AFO’s in Spastic Cerebral Palsy
The thermoplastic molded ankle foot orthosis was first described in 1958 by Yates who used it in the treatment of a flaccid foot drop.5 Subsequently, it was used in childre with spastic cerebral palsy. In order to evaluate it’s effectiveness, two questions should be asked: What are the orthotic management goals in spastic CP, and are AFO’s effective in obtaining those goals? The three goals for these orthotic devices would be 1) correction, prevention or delay of contractures, 2) facilitation of function or ambulation, either by obtaining functional goals at an earlier time, improving the parameters of gait, and/or reducing energy expenditures and 3) the reduction in proximal muscle tone in order to facilitate functions at a higher level.

How do these orthoses work? The AFO provides a means of controlling or eliminating ankle and subtalar motion. By controlling the more distal joint, one can theoretically alter the GRF and effect more proximal joints by the principal of coupling. The standard construction of a solid AFO is to place the foot plantigrade, the subtalar joint in neutral, or physiologic valgus, and the ankle joint in neutral. One should bring the trim lines anterior to the malleoli in order to maximize the resistance to the anterior bending moment and improve medial lateral stability. The foot plates should be brought out to the end of the toes. Two straps are necessary, one proximal to maintain the shank within the orthosis, and one at the level of the ankle to be sure that the heel fits snugly into the orthosis and cannot rise. (Figure 3) This is a more effective way of keeping the orthosis snugly on the foot rather than depending on a high top shoe to keep the orthosis properly positioned. If one places the ankle in slight dorsiflexion, this results in the GRF moving posterior to the knee joint, resulting in a flexion couple acting at the knee joint and would theoretically be of value in correcting a back knee hyper extension type gait. (Figure 4)

Conversely, if one places the foot in slight equinus, this results in the GRF moving anterior to the knee joint, and produces a knee extension moment. This theoretically would be a value in a crouched type gait with knee flexion. (Figure 5) Modifications to the heel or sole of the orthosis create the same affects on knee motion as alteration of ankle angle at casting. A heel raise creates the same affect as ankle dorsiflexion, and placing a lift under the sole of the orthosis has the same effect as placing the ankle in plantar flexion. It is sometimes easier to mold all of the orthoses with a neutral ankle and then fine tune the orthoses by placing various lifts under either the heel or sole depending on the effect desired. One is then able to add or subtract until the desired effect has been achieved.6 Always keep in mind the type of footwear preferred by the patient. Usually the AFO is worn with a flat heel/sole shoe such as an athletic shoe. If one then switches to a dress shoe with a small heel, this will have the same impact as adding a lift under the heel, moving the GRF posterior to the knee joint and causing a knee flexion moment.

Two very important points must be emphasized in prescribing and fabricating AFO’s. First there is no scientific evidence documenting that AFO’s will correct a fixed deformity, in fact, most physicians feel that one must first correct the fixed deformity by the use of therapy, stretching and serial casting or surgery before the AFO is fitted. The second important concept that must be kept in mind is that not only must the ankle joints have sufficient flexibility to be affected by the AFO, but in addition, there should be no significant fixed contractures of the joints above. We can not expect an AFO placed in mild plantar flexion to improve a knee flexion deformity if the contracture is fixed. Sankey, et al. described two groups of patients treated at the same institution with two different design type AFO’s. In one group, the AFO was constructed with the ankle in mild plantar flexion, the toe plate ending behind the metatarsal head and no ankle strap to maintain the heel snugly in the orthosis. The second group had a new design with the ankle in mild dorsiflexion, an ankle strap to maintain the heel in the orthosis, and the foot piece extending to the ends of the toes in order to reduce the risk of stimulating plantar grasp. There was a striking difference in the latter group in the need for surgery with none of the group, either having or contemplating a surgical correction of their equinus. Their conclusions support the concept that AFO’s can delay or prevent contracture of the gastrocnemius in spastic children. 7 Other researchers have documented improvement in gait patterns in spastic children utilizing AFO’s of various designs. 8 9 10 11 It has been demonstrated that gait deviations in children with cerebral palsy have been shown to increase energy demands nearly three-fold compared to healthy children, and in addition these children walk at a reduced velocity.12 Reduction in energy expenditure and an increase in the velocity of walking is a secondary advantage in using AFO’s in spastic cerebral palsy.13

We can conclude from the available scientific literature that AFO’s do prevent or delay fixed contractures, improve function of ambulation by improving the parameters of the gait, increase velocity and reduce the energy demands for ambulation in spastic cerebral palsy.

Articulated or hinged AFO’s
It is not surprising that professionals would attempt to modify the standard solid AFO to see if further improvement could be benefitted. A moveable ankle joint was added which had the advantage of maintaining medial and lateral stability at the subtalar joint and foot, while at the same time permitting some or all ankle motion. (Figure 6) A modification of the articulated AFO is the SMO (super malleolar orthosis). (Figure 7) In essence, the anterior and posterior portions have been removed resulting in mediolateral stability with essentially free ankle motion permitted.

Carlson, et al, compared the SMO, fixed AFO and no brace in spastic diplegia. His conclusion was that only the AFO had a positive effect on ankle motion and improved energy efficiency.14 Wilson, et al demonstrated that sit-to-stand in pre-ambulatory spastic children was significantly improved with the use of an articulated AFO which permitted dorsiflexion. They demonstrated that sit-to-stand in both normal children and CP children who can do this maneuver, requires ankle dorsiflexion. Conversely, uncontrolled dynamic ankle equinus interfered with sit-to-stand in these children. By using the articulate AFO, which is equipped with a 90 degree plantar stop which controlled the equinus, but permitted dorsiflexion, this prerequisite to pre-walking was improved.15 Other authors have demonstrated that walking velocity and a more natural appearing gait were improved by the use of articulated AFO’s which prevented plantar flexion, but permitted a freedom of dorsiflexion. 16 17 This must be weighed against the increased complexity of the design and the possibility of increased fabrication errors.

Inhibitive Casting and Dynamic AFO’s
Can AFO’s reduce tone in muscles proximal to the AFO and thereby improve function? This question has been raised among the orthopedic, physical medicine, physical therapy and orthotic communities. In order to comprehend the proposed mechanisms of the dynamic AFO’s (DAFO’s) we must first understand the concepts of inhibitive casting, and the subsequent adaptation of these techniques to AFO construction. The concept of inhibitive casting in the treatment of spastic cerebral palsy was first introduced by Mott and Yates in 1977.18 They presented a series of 111 children of which 68% were predicted to be nonwalkers. After treatment with inhibitive casting, 64% became independent walkers, 20% walked with aids and 14% remained nonwalkers. Their work was based on the observations of Duncan.19

Duncan, an orthopedic surgeon observed certain reflex patterns seen in many children with spastic cerebral palsy and postulated that retention of these primitive reflexes might lead to the production of deformities. (Figure 8) The toe grasping reflex, stimulation over the second and third metacarpal heads and base of the second and third toes, would result in a flexion and adduction of the toes augmenting a tendency for forefoot plantar flexion. The inversion reflex resulted from stimulation of the medial border of the foot resulting in an inversion deformity of the foot. The eversion reflex resulted in eversion of the foot with stimulation over the lateral border of the foot and the fifth metatarsal head. The dorsiflexion reflex resulted in dorsiflexion of the foot in response to stimulation of the central surface of the heel. He suggested that these reflexes remain in certain children with cerebral palsy and may lead to deformity. Utilizing the principals of Duncan, Mott and Yates suggested that stimulation over the heel would cause the foot to go into dorsiflexion, thus decreasing the equinus tendency. Conversely, by eliminating the stimulus of the toe grasping reflex by bringing the foot plate past the metatarsal heads and slightly dorsiflex the toe would decrease the toe grasping reflex and decrease the potential development of equinus. If the child has a tendency toward inversion and/or varus, then reduction of the stimulus over the medial border of the foot and first metatarsal head would decrease this response, and conversely, valgus of the hindfoot and eversion of the forefoot could be reduced by decreasing the stimulation over the lateral aspect of the foot and the fifth metatarsal head. They suggested that these reflexes be evaluated, and if present, modification of the foot plate in the cast would be of positive value. All proponents of inhibitive casting stress that this modality is not a treatment of itself, but an adjunct to neurodevelopmental therapy techniques and is never used in isolation. The techniques of inhibitive casting were described in a subsequent article by Duncan and Mott.20 They stress three principals in proper construction of the inhibitive cast: 1) proper contouring of foot plate to add areas of stimulation to stimulate desired reflex areas and reduction of contact with reflexogenic areas of overactive tonic reflexes, 2) correction of existing deformities and 3) proper alignment of the ankle and subtalar joints in their physiologic position.

A number of authors have reported favorable results with the use of tone reducing casts. Sussman and Cusick reported improvement of patient’s functional status in a neurodevelopmental program which included inhibitive casting. This study had no control group and could not separate out the effects of casting, per se, from inhibitory foot plate.21 Zachazewski, et al reported favorable results in a single patient study in decreasing the positive support reaction in adult with traumatic spasticity. The use of tone reducing casts improved ambulatory function and when casting was discontinued, the positive support reaction returned.22 Hinderer, et al, utilizing a single subject design with two spastic diplegic children, demonstrated increase in stride length and subjective impressions of improvement in gait patterns by the evaluating therapists.23 Bertoti evaluated two groups of children with cerebral palsy with and without tone-reducing short leg casts. Short leg casts demonstrated improvement in muscle tone, trunk control and gait symmetry. The casted children demonstrated significant improvement in passive and active mobility of the pelvis, trunk and lower extremities.24

Odeen and Knutsson evaluated the effects of muscle stretch and weight load in patients with spastic paraplegia. They demonstrated a significant reduction in muscle tone, measured as decreased torque with a strain gauge transducer, of passive ankle plantar flexion and dorsiflexion and change in EMG activity of gastrocnemius and tibialis anterior muscles; with both standing and ankle in dorsiflexion with the largest reductions in muscle tone obtained by combined weight load (standing) with stretch imposed upon to calf muscles (ankle in dorsiflexion).25 This study would suggest that tone reduction may be due to the effects of muscle stretch and the weight bearing position, not secondary to the effects of the inhibitory foot plate. Watt, et al, studied 32 cerebral palsy patients in a prospective study of a trial of inhibitive casting and neurodevelopmental therapy for a three week period. They noted an improvement of passive range of ankle dorsiflexion and improvement in spastic gait pattern at three and five weeks after casting which deteriorated to precasting values at six months.26 Odis, et al, studied 16 spastic extremities utilizing short leg tone reducing casts. He found no effect, positive or negative, on the muscles or joints above the area casted and was not able to separate out the benefits of the short leg cast versus the inhibitory footplate.27 Mills studied effects of inhibitory casts on 8 subjects with neurologic insults using EMG activity and range of motion evaluation. He noted that the range of motion and dorsiflexion at the ankle improved, but there was no effect on integrated EMG activity during splint use.28 Sussman, an early enthusiast of inhibitory casting, suggested that the tone reduction is caused by muscle atrophy and that the casts function in a similar manner to rigid ankle foot orthoses which maintain the foot and ankle in a neutral plantigrade position, thus stabilizing the base of the support.29 Thus, it would appear that the concept of inhibitive casting is based on sound clinical observations, and that the use of inhibitive casting can improve the children’s function, but it has not been shown that the inhibitive footplate is responsible for these improvements or reduction in tone of proximal musculature. The controversy remains as to the etiology of the improvement. Is it the inhibitive casting with the reduction and stimulation of the primitive reflexes or simply the neutral stabilization of the ankle and subtalar joints and stretching of the gastroc soleus muscle group with subsequent atrophy, and therefore, weakness to the gastroc soleus?

Dynamic AFO’s
The proponents of dynamic AFO’s (DAFO’s ) or tone reducing AFO’s (TRAFO’s) stress that the construction of this type of AFO requires a very thin, flexible, super malleolar type of orthosis which permits some ankle motion, a form fitting orthosis which maintains the subtalar joint in neutral and supports of the natural longitudinal and transverse arches of the foot, as well as the unique construction of the foot plate. (Figure 9) Two authors have demonstrated an improvement in tone of the muscle groups cephalad to the orthosis. Taylor and Harris, in a single subject design, noted an improvement to upper and lower extremities as measured by ball catching ability, length of stride and improvement on the Peabody motor scale. 30 Oshawa, et al. evaluated 39 spastic patients utilizing the tone reducing AFO’s. They noted a correction in drop foot, reduction in tone in the gastroc, hamstrings and quadriceps muscle activity as measured by EMG.31 Other studies have demonstrated an improvement in gait patterns while utilizing inhibitive, tone reducing ankle-foot orthoses.32 33 Three studies in the literature compared tone reducing AFO’s with solid AFO’s. Hinderer, et al, in a single subject design of two children with spastic diplegia demonstrated an improved stride length in the tone reducing orthoses and a subjective improvement in gait patterns as viewed on videos by trained physical therapist, who were blinded to the type of orthosis used.23 Two additional studies comparing these two types of orthoses demonstrated that both types improved gait patterns and alignment over no orthoses, but they could find no scientific evidence that supported the superiority of the tone reducing orthoses.34 35 In conclusion, there is scientific evidence both in support of and against the concept that DAFO’s are capable of reducing tone in muscle groups above the area braced, and therefore, by reducing tone, improving function. However, there is strong support, based on the scientific literature, that AFO’s off all designs improve gait function when compared to no orthoses in the treatment of spasticity.

Orthotic prescription
From a practical viewpoint, how should the physician, therapist or orthotist approach the spastic patient from an orthotic viewpoint since they have multiple options to choose? A number of parameters should be ascertained before writing the prescription.

What is the purpose of the orthosis? Do we want to maintain the ankle-foot in physiologic position to prevent or delay contractures in a nonambulatory patient? If so, the simplest and least expensive AFO is needed. Is the purpose of the orthosis to speed the development of sit-to-stand in the diplegic child? If so, then an articulated AFO or SMO, which permits dorsiflexion, is indicated. Are dynamic or fixed deformities present? Keep in mind that one must evaluate not only the foot-ankle, but also the knee and hip, especially if we want the orthosis to affect the proximal joints. A floor reaction AFO will not improve a crouch gait if the knee and/or hip flexion are fixed deformities. Whenever possible, fixed deformities should be corrected prior to bracing. For the principle of coupling to be effective, the adjacent joints must have the capacity to be placed in the correct position.

What are the functional needs and/or ambulatory goals of the patient? A different prescription is needed for a high functioning individual. One might choose a articulated AFO for the minimally involved or a posterior spring leaf orthosis if the main functional need of the patient is correction of foot drop in the swing phase of gait. If there is excessive tone in proximal muscle groups, then a DAFO should be considered.

What type of material should be used in the fabrication of the orthosis? A floor reaction AFO to control knee flexion necessitates a rigid construction to prevent unwanted ankle motion and to transmit the force from the foot to the anterior proximal tibia to correct knee flexion. Thick polypropylene is ideal for this construction. A flexible, material such as thin polypropylene is best suitable for DAFO’s since intimate fit and a degree of flexibility is desired. In the posterior leaf spring AFO, we do not need or want rigidity to control medial or lateral stability, but need a material that is flexible to permit dorsiflexion of the foot in midstance and to store energy for push off. In addition, the material must be durable enough not to fail because of repeated bending. Copolymer is a good consideration for this type of AFO. Obviously, the orthotist with his familiarity with different materials, will be primarily involved in this area.

Winters, et al evaluated 46 patients with spastic hemiplegia and classified their gait patterns.36 Let us use some of his examples to identify what type of orthoses might be of benefit. In group 1, the gait pattern characterized plantar flexion of the ankle in swing phase with pure equinus deformity on contact. He suggested that this problem is probably due to the weakness in the dorsiflexors, rather than to over activity of the gastroc soleus muscle group. A leaf spring AFO, which essentially offers no medial lateral support, but would improve foot clearance during swing, and at the same time permitting dorsiflexion of the foot in midstance, would be of benefit.37 (Figure 10) The second group identified had a static or dynamic equinus that resulted in persistent plantar flexion of the ankle during stance and swing phase. The prescription in this case would be first, correction of the equinus deformity if static, and then application of a solid AFO or dynamic AFO to control the equinus. The solid AFO could be articulated or hinged, if desired, to permit some dorsiflexion.

As noted earlier, if the amount of equinus is small and the foot, despite the equinus, is capable of a plantigrade relation to the floor, a compensatory hyper extension of the knee is often present. In this case, a solid ankle AFO constructed either in 5 degrees of dorsiflexion or neutral ankle with a heel lift, will result in a flexion moment at the knee and improve the genu recurvatum.7 11

Finally, we are all familiar with the complication of over lengthening the Achilles tendon with the iatrogenic production of a calcaneus deformity. As the foot goes into dorsiflexion, the ground reaction force is moved posterior to the knee resulting in a flexion moment, and anterior to the hip joint resulting in a flexion moment. The end result is a classic crouched gait. Consideration of an AFO with the ankle joint in plantar flexion or conversely, elevation under the sole in a neutral floor reaction AFO results in an anterior shift of the GRF resulting in an extension moment to the knee and the hip. As mentioned previously, it is imperative that there be no fixed knee or hip flexion contracture since these orthoses will not correct fixed deformities.7 38 (Figure 11)

Let us revisit our initial question regarding the use of AFO’s in spastic patients. Do AFO’s work? Without question the scientific literature demonstrates that AFO’s are a positive benefit in spasticity. They will delay or prevent the development of fixed deformity, but will not correct fixed deformity. They improve the parameters of gait, such as improved stride length, reduction of energy expenditures and can give the patient a more natural appearance while ambulating.

What is their purpose and how do they work? The purpose of the AFO’s is to directly control the foot-ankle and indirectly affect the knee and hip to prevent that the later explanation for the demonstrated reduction in proximal muscle tone is best supported by literature review.contractures and improve gait parameters. There is strong and convincing evidence in the medical literature to support this conclusion.

Do AFO’s reduce tone in proximal muscle groups and thereby improve function? I believe this concept can be supported by scientific study. Is the tone reduction secondary to inhibitive foot plate design or to the use of the properly constructed AFO which places the foot and ankle in the physiologic position, prevents unwanted motion, maintains prolonged stretch, permits weight loading in the standing position and results in a degree of atrophy and weakness to overactive muscles? I believe that the latter explanation for the demonstrated reduction in proximal muscle tone is best supported by literature review.