A Dynamic AFO is a very thin flexible supramalleolar orthosis with a custom contoured soleplate to include support and stabilization to the dynamic arches of the foot. Many aspects of the brace appear critical in nature. When these have been accidentally modified, orthotic control has been significantly diminished. Placement of the D-ring ankle strap at 450 with pull to the back of the heel appears crucial for many individuals with high tone to hold the heel securely in the orthosis. Posterior trimlines are also crucial. The bottom of the posterior cut-out needs to be just above the level of the ankle fulcrum of movement to get complete coverage of the calcaneous and allow comfortable ankle movement. A narrow posterior opening provides more complete medial-lateral control. Forefoot strap provides integrity to the anterior portion of the orthosis to maintain total contact and support to the forefoot and toes. The toe loop is incorporated in almost every instance to provide neutral stabilizing forces to the first digit and metatarsal phalangeal joint.
Though there has been limited research and published articles to date on Dynamic AFO (DAFO) and Dynamic FO (DFO) systems, they have been in use with a pediatric population clinically for about 10 years. The clinical advantages of these systems are nu merous. They differ dramatically from conventional orthotic systems in several ways (Figure 1) .
Because of the supramalleolar construction with a posterior cut-out, DAFOs allow varying degrees of movement into plantar and dorsiflexion along the natural axis of ankle movement (Figure 2) . Normally small amounts of adduction and inversion accompany plantarflexion and small amounts of abduction and eversion accompany dorsiflexion because of the orientation of the ankle axis. These small increments of inversion/eversion. are very involved posturally with graded control involving balancing strategies at the hip, pelvis and trunk. It is impossible for normal postural components of movement to occur at the pelvis, trunk and shoulders when the patient is on all fours or during floor lying activities if the ankle is fixed at 9()0 Normally the ankle moves in these positions through varying degrees of plantarflexion. Inversion occurs more on the side to which weight is shifted and is very connected to pelvic and trunk rotational movement components necessary to maintain graded postural control. Lversion occurs more on the side that is taking less weight and connects similarly with total postural control. Similar postural connections are present in all normal upright activities as well. A standard fixed-ankle or jointed-ankle orthosis does not allow these strategies to take place, limiting balance and postural control possibilities.
Most of the important joints of the foot, like the ankle, are also triplane in nature, with movement components in all three planes of movement.2 In triplane joints, movement components in each plane are interconnected. If movement is restricted or stabilized in one or two planes, the movement in the third plane will be more graded and stable. Because DAFOs are designed to provide secure medial-lateral ankle stability and midline positioning, they may restrict and stabilize inversion/adduction and eversion/abduction components of ankle movement sufficiently to provide improved stability and grading of plantar and dorsiflexion. This may be a partial explanation for the typical clinical finding of reduced abnormal plantarflexion while wearing DAFOs in children with moderate to severe dynamic equinus.
Support to the medial-longitudinal arch and peroneal notch area provide a significant upward and medial-lateral stabilizing effect on the subtalar joint around subtalar neutral without completely blocking the movement of the joint. Because it is also a triplane joint and because it has a tremendous impact biomechanically on the stability of the entire foot, providing very precise stabilizing control to the subtalar joint could also have an impact on the person's ability to actively control the foot and ankle. It is a repeatable clinical phenomenon that even slight dorsiflexion of the toes has a tone reducing impact on abnormal extensor synergy posturing throughout the lower limb. Whatever the reason, often a significant decrease in equinus is seen clinically, even with the use of only DFOs.
A fellow therapist relayed the following experience regarding a 15 year old girl with mild to moderate diplegia. The therapist had been working for almost one year to develop 1-leg standing balance and the girl's progress had improved over that period of time. A very resistant heelcord contracture on the right side limited dorsiflexion just to neutral, and restricted her balancing possibilities. Within three months of initiating wear of bilateral DFOs and following the exact same therapy regime, the girl had gained 15° of passive dorsiflexion with an extended knee.3
Often when children outgrow DAFOs or DFOs, increased heelcord tightness is noted. With new orthoses the tightness can usually be actively stretched or reduced within a fairly short period of time. Sometimes if the foot is left too long in an ill fitting orthosis or without an orthosis, inhibitive serial casting may be required to regain ankle range before molding for a DAFO.
DAFOs differ significantly from conventional orthoses in their extreme flexibility. Typically they are pulled from 3/32" polypropylene and stretched almost paper thin across the anterior portion. Anterior trim- lines can almost meet down the center of the dorsum of the foot in a DAFO and the orthosis of the most ideal thickness can be opened up easily beyond its most lateral borders or twisted in several directions (Figures 3a and 3b) . It appears flimsy and completely incapable of surviving typical abnormal gait stress-Cs in C.P. ambulators, if not totally incapable of providing support to strong abnormal tone force. Because it is a volume critical orthosis, much like a prosthetic socket, the fluid pressure and volume of the person's foot within the orthosis gives it much greater stability and strength while allowing small increments of movement within the foot to occur. This has at least three positive effects:
The DAFO is tolerated more easily than conventional plastic bracing, even in cases of extreme and difficult to manage spasticity. Allowing some sensation of "give" to the brace reduces the tendency of the person to "hold" forcefully against any portion of the brace. Because it is total contact, pressures are distributed much more evenly throughout the brace, reducing the tendency for skin breakdown. Skin breakdown problems are essentially non-existent in a well fitting DAFO, even in cases of repeated breakdown and fit problems with conventional AFOs (Figures 4a-4d) .
Small increments of movement around midline normally happen both in weight bearing and non-weightbearing situations as a part of normal balance strategies. Extremes of movement or fixation are not normal and do not provide normal proprioceptive feedback information to the postural control mechanism within the central nervous system. A more stable and consistent proprioceptive feedback system can provide more helpful and reliable information for balance and postural control.
An interesting example of the value of the proprioceptive feedback system provided by DAFOs and DFOs is seen in a six year old boy with Usher's Syndrome. In this syndrome, individuals are born deaf or hard of hearing and gradually lose vision with increasing "tunneling" and cataracts. Vestibular feedback from the semi-circular canal appears partially or totally non-functional. Proprioception appears to remain completely intact and is used extensively and in an amazingly refined way for communication to read "tactile signing." The individuals are generally of normal to above average intelligence. With decreasing vision, increasing difficulties with balance occur, sooner and to a greater extent at night. This particular child was already operating visually in a fairly narrow tunnel and was having considerable difficulties with maintaining static standing balance, walking balance, falling while running and during field activities, even though he was very strong and well coordinated with no true motor impairment. The use of DFOs dramatically affected his function and balance. Because the DAFOs offered a consistent and stable proprioceptive feedback to supplement visual and vestibular deficits, immediate changes in posture and stability were noted. His therapist and mother noted dramatic improvement in his ability to stand still and walk a balance beam and noted a dramatic decrease in falling. By training this child to use this new proprioceptive information from his feet in a very refined way, hopefully he will not experience the typical severe balance difficulties associated with Usher's Syndrome as his vision decreases.
Training was done on a mini-trampoline first with eyes open and later with eyes closed-to focus completely on the proprioceptive feedback and to force the proprioceptive system to refine its control.
This is an intriguing example of creative application of orthoses providing new information to improve our understanding of how and why DAFOs and DFOs improve function, postural and tone control in cerebral palsy. In cerebral palsy proprioception is often disturbed, sometimes because of inconsistent feedback from posturally unstable soft tissue structures and joints; sometimes as a primary neurological deficit; and in many instances as a combination of both. Anything that allows greater postural security and stability with movement will provide improved feedback to the system and thereby affect movement control and function in a positive way.
The very precise support to the sole of the foot found in DAFOs and DFOs is significantly different from conventional AFOs or even other systems of so-called "tone reducing," "inhibitive," or "dynamic" bracing. A custom contoured footboard is used to provide support to the natural arch contours of the foot. The foot is maintained in neutral alignment with muscle tone controlled throughout fabrication. An exact drawing of the individual's foot in nonweightbearing neutral alignment is used for footboard fabrication. Routing or hollowing at a depth of 1/8" under the metatarsal head pad area and the calcaneous pad provides stability and circumferential support to these crucial weightbearing areas (Figure 5 and Figure 6 ). Plaster buildups under the medial-longitudinal arch and peroneal notch provide support and stability to the rear-foot and subtalar joint. Plaster build up under the soft tissue cavity proximal to the metatarsal heads provides improved midline forefoot stability. To avoid supporting this area too much, the metatarsal pad area should sit completely into the routed area with the toes held in dorsiflexion. The plaster build up is blended into the medial-longitudinal arch for greater pressure distribution to the sole of the foot. Plaster build up under the toes is designed to bring them to horizontal dorsiflexion only in order to allow active dorsiflexion and plantarflexion at the MP joints to occur. Accommodation is also made for varying thickness of toe fat pads and natural arched areas just distal to the MP joints (Figure 5 and Figure 6 ). In general, the greater the degree of instability and/ or hypertonus the greater the support required into these soft tissue contours. Support of soft tissue arching areas maintains boney configurations in the foot in a much more normal and functional position through fluid pressure (Figures 7a and 7b) . Total contact support allows these pressures to be distributed more evenly for better tolerance. Because the support of these soft tissue areas is so important for control and stability of the foot and ankle, the soleplate contour may appear extreme in comparison to the visible contour of the person's foot. The reaction to this support is generally very positive during the molding process and later. Tone changes in the foot, lower extremity and total body are very important feedback as to proper support and contouring.
In one unusual instance, a two and a half year old girl with a moderate mixed quadriplegia and significant proprioceptive and tactile hypersensitivity complained for the first two days of wearing the orthoses, especially when they were first applied. On the third day she did not want to take them off-even when she went to bed. Suddenly, the new and consistent proprioceptive feedback and stability had become acceptable to her system and she did not want to lose that feeling. It is interesting that children accept these orthoses fairly easily and tend to like them. An exception to this rule is those individuals who are very used to using significant abnormal tone for function. In these cases considerable effort by the therapist is needed to help the individual accept a very new method of control in their bodies. Sometimes it even means temporarily giving up a certain level of function, such as walker ambulation, in order to gain a higher function of independent standing balance and walking. Such decisions are best made by a highly skilled pediatric therapist.
DAFOs and DFOs are primarily a specialized therapy tool that allows more rapid acquisition of postural control and function in individuals with various disturbances of posture and movement. They should be used only in conjunction with an active postural control and balance oriented therapy program. Therapy orientation often must change to become much more active. Active stimulation of balance, normal postural tone and progravity weightbearing responses upon the initiation of treatment with DAFOs and DFOs achieves the best results. We have found that very active work on shoulder/trunk/hip postural control and balance while sitting on a gymnastic therapy ball (Figures 8a and 8b) and progravity work in the "bear position" or modified "bear position" (Figure 9 and Figure 10 ) tends to be helpful in maintaining stability and balance necessary to prepare for independent standing and walking. In ambulators and potential ambulators, active work to teach balance and control over a single leg can also be done effectively using the gymnastic ball (Figure 11) . This kind of therapy orientation is crucial in order to take optimal advantage of the DAFO or DFO system.
This orthotic system has been used successfully at our center and numerous other centers in the U.S., Mexico, and Canada with such varied diagnoses as arthrogryposis, spina bifida, congenital hypotonia, Duchenne's muscular dystrophy, congenital club foot with hypotonia, post head injury, anoxic encephalopathy and cerebral palsy. In some cases of individuals with the L 3-5 spina bifida who require a knee extension assist and individuals with cerebral palsy who have a severe crouch gait, the soleplate contouring has been made a successful part of floor-reaction orthoses. In cases of severe arthrogryposis the soleplate contouring has become a part of a very thing short-leg AFO. A close professional association with Don Buthorn, C.P.O., led to the development of minimum, moderate, and maximum control DFOs (Figure 12) as well as short floor-reaction dynamic bracing (Figure 13) and other new configurations. This new approach to orthotics has evolved from practitioners' creative responses to differing patient needs. DAFOs with a fixed plantarflexion stop are infrequently used in cases of persistent strong equinus, which significantly interferes with upright function, weightbearing and balance (Figure 14) . An adjustable posterior Velcro strap is commonly used to provide a measure of plantarflexion control (Figure 2) . Straps can be fastened snugly for greater equinus control in upright activities and loosened for floor and transitional activities allowing for optimum pelvic and trunk rotational movement components to occur. Similarly, an anterior Velcro strap can be used as a partial plantarflexion assist. If a full dorsiflexion stop is required, the plastic generally requires some reinforcement across the ankle and a D-ring anterior strap at the top to provide secure support to the plastic.
Since 1984, extrinsic biomechanical forefoot posting has also been incorporated into DAFOs and DFOs when familiar biomechanical variations are present and contributing to mechanical instability and tone control problems. This has made it much more possible to manage the often extreme pronation or supination problems that result when bony forefoot varus or valgus are present. Rearfoot varus posting is intrinsically managed in the orthosis. The aim has been to provide maximum postural control, stability and usable proprioceptive feedback with the least bracing and impairment of movement. Whenever possible, very thin polypropylene is used.
Cerebral palsy diagnoses in which DAFOs and DFOs have proved helpful vary from severely involved multiply handicapped youngsters to children with very mild coordination and balance disturbances. In severely involved individuals DAFOs with free plantarflexion allow for improved symmetry and ease of positioning in wheelchairs, prone standers and other positioning devices, as well as ease of handling at home or in therapy, improved oral motor control and general postural and tone control (Figure 15) . In less severely involved individuals DAFOs and DFOs open new possibilities for development of balance and control in sitting, standing, walking and more complex upright skills. A moderately involved three year old child with spastic diplegia with DAFOs is able to successfully work on independent standing balance with hip abduction extension and neutral rotation, but finds this impossible to control without DAFOs. A mildly involved posturally disorganized child who can stand and balance on one foot, skip and jump, and walk a balance beam using easily fabricated Pe-lite DFOs, finds all these tasks very difficult to impossible when the DFOs are not in his shoes. A six year old girl with moderate to severe hemiplegia is more able to weightbear and balance over the involved leg and use the involved arm and hand when her DAFO is on.
Functional expectations of an orthotist or therapist need to adjust to any new tool. DAFOs and DFOs are no exception. As a general rule, the expectations we have for balance, postural control and functional skills can shift for a moderately involved child to become that of a child with mild involvement. In a child with more severe tone involvement, expectations can shift toward more moderate involvement with consistent use of DAFOs and an active therapy program. It is common within our experience for children with a moderate spastic hemiplegia to walk on a balance beam for-ward and backward and for children with mild to moderate diplegia to develop fairly normal flow of gait and run.
Clinical application and use of tools is often years ahead of documented research. Though two clinical studies of DAFOs have been published showing improved acquisition of standing balance and improved upper extremity functional performance in children with cerebral palsy, there is a need for more clinical research with varying populations and parameters.4,5 In addition to the .published studies, I am aware of at least two unpublished studies regarding DAFO influence on gait parameters in adult hemiplegia and in children with hypertonia.6,7 As further research becomes available, we will continue to use and refine these tools based on feedback from our patients. In the final analysis they are our only meaningful critics and the reason DAFOs and DFOs exist at all. If we can make life easier a nd more productive for someone, it is worth all the effort and we are a success.
I would like to thank Don Buthorn, C.P.O .,for all of his help in reviewing and editing this article, and for his close, professional association in the recent developments of dynamic orthotics
Thanks also to all the staff of Children's Therapy in Kent for their patience and support for my explorations into the field of orthotics
Nancy Hylton is presently a practicing pediatric physical therapist and consultant at Children's Therapy Center, Kent, Washington. She is the co-founder of Children's Therapy Center of Kent and is an NDT assistant instructor for pediatrics. She has been in pediatric practice for 20 years and has taught numerous workshops and courses on casting and orthotics in the United States, Canada and Mexico over the last 10 years. She has been actively involved in the development and refinement of dynamic casting and orthotics in the Seattie area since 1971.