Seating for Cerebral-Palsied Children

ELAINE TREFLER, O.T.R. ROBERT E. TOOMS, M.D. DOUGLAS A. HOBSON, P.ENG.


Commercially available seats are seldom adequate for children with significant physical handicaps. Conditions such as spasticity, athetosis, floppy postures, or severe fixed deformities of the extremities and/or spine necessitate an individualized approach in solving the seating problems of these individuals. The challenge is to meet the specialized seating and mobility needs of this group of handicapped children with a system that is economically feasible, instead of providing expensive customized seating for each child. With the advent of rehabilitation engineering progranls, it has been possible to develop a systematic approach, combining modern technology and therapeutic concepts, to solve this complex problem.

Seating systems are an essential component of the overall management of any child who must spend the greater part of his day in a wheeled device. From a global viewpoint, good seating should provide medical, functional, and social benefits to the physically handicapped child and his family. From the medical point of view, the primary concern in seating cerebral-palsied children is preventive in nature. As they grow, these children often develop peripheral joint contractures, dislocated hips, scoliotic curves, and other skeletal deformities. Through an appropriate seating posture, many of these problems can he prevented completely or at least retarded in development. In considering the seating management of cerebral-palsied children, one must consider not only the orthopedic disabilities, but also the fact that we are dealing with pathological reflex patterns. The two persistent pathological reflexes which most often cause problems in properly positioning the young child with cerebral palsy are the asymmetrical tonic neck reflex (ATNR) and the positive supporting reaction. A strong extensor thrust must also be overcome in order to provide good seating.

The ATNR prevents the child from holding his head in the midline and from using his hands together. The ATNR is clinically manifested by the child in turning his head strongly to one side, extending the arm on the side toward which the head is turned, and flexing the opposite arm. If this posture persists, scoliosis will often develop, since the characteristic head position is accompanied by rotation of the spine. With the positive supporting reaction, any pressure on the ball of the foot stimulates simultaneous contraction of both the flexor and extensor muscles in the lower limbs, but with greater extensor spasticity, resulting in stiffly extended legs.

Because of the tonic labyrinthine reflexes, children who are seated in an upright position exhibit an increase in extensor tone of the neck and back muscles after initially experiencing flexion of the spine and protraction of the shoulders. These tone changes make the angle at which the child is seated critical for providing maximum security, comfort, and support.

The degree of muscle tone is critical in decision making. The spastic child has too much tone in both the flexor and extensor muscles at all times, resulting in a rigid posture. The athetoid child experiences fluctuating muscle tone which results from alternate firing of flexors and extensors. Finally, the floppy or hypotonic child has too little tone in both flexors and extensors, resulting in a "rag-doll" posture. In all cases the children should be seated so as to normalize muscle tone and encourage appropriate motor development.

Seating is as important from the functional viewpoint as it is from the medical perspective. When a child is properly seated in a stable, comfortable manner, many functional activities are improved. A stable trunk posture enhances development of fine motor skills such as holding a spoon or pencil, pointing on a communication board, or operating a typewriter. Children in educational settings can put more of their effort into learning activities if they are not constantly fighting for trunk and head stability.

Finally, one must not overlook the positive social impact that a good seating and mobility system can have on the handicapped child and his family. Too often we see parents who must physically carry their handicapped child from place to place in their arms because an appropriate seating system is not available to them. As parents get older and become physically infirm and the child grows larger and heavier, transport becomes an increasing difficulty. As a consequence, one or more family members are forced to stay at home with the child, and the family unit is unable to participate in family recreational and social activities. Eventually, institutionalization may become the only acceptable alternative. In such circumstances, a properly designed seating system, even though it may not offer medical or functional benefit directly to the child, can often make a tremendous difference to the family unit in terms of easeof management.

Philosophy

Upon analyzing the total scope of the seating problem of the cerebral-palsied child, two major variables were identified: clinical diagnosis (athetosis, spasticity, etc.) and the severity of the clinical symptoms. In our experience, the severity of the disability is a more reliable indicator of the type of seating required than the clinical diagnosis, i.e., it is more important to know the degree of the child's physical and mental involvement than to know whether he is an athetoid or spastic. Therefore, for purposes of seating design and prescription, we have arbitrarily classified children into three categories based on the severity of their involvement: minimal, moderate, and severe ( Figure 1 ). We have defined the minimally involved child as one who has good head control and fair trunk control but who is somewhat unstable in the sitting position. These children often have good use of their hands for fine motor skills, if they are seated in a stable position. We have defined the moderately involved child as one who has fair head control, poor trunk control, and only moderate use of his hands. The severely involved child is one who has poor head control, poor trunk control, often severe spinal curvatures, and virtually no use of his hands in the sitting position. In addition to defining the extent of the physical involvement, it is also essential to know the level of intellectual functioning, since the functional seating needs will vary according to the degree of mental retardation present. Finally, one must consider whether the seating system is to be designed solely to help the parent in management of the child, or whether one is attempting to assist the child towards improved motor development. The following systems have been developed on the premise that the child's degree of involvement is of primary concern, Whenever possible, improved motor development is strived for through incorporation of therapeutic concepts into the seating system.

The Child with Minimal Physical Involvement

Children with minimal involvement sit fairly well in a standard wheelchair. However, the shape of the hammock-type seat of the standard wheelchair can introduce sitting instability. Also, because of their muscle imbalance and poor trunk control, these children can develop scoliotic curves and pelvic obliquities quickly. Therefore, it is important to provide a minimally involved child with a firm sitting surface, both for stability and to encourage equal weight distribution on both ischial tuberosities. This type of child can often he accommodated in a simple wheelchair insert, installed into a commercially available wheelchair ( Figure 2 ). The inserts can be made of 12-mm (1/2-in.) plywood which is covered with foam and upholstered with vinyl or heavy cotton material such as denim. The seat portion is usually raised 2.5 cm (1 in.) anteriorly to help the child sit well back in the chair. The hack portion of the insert corresponds approximately in height and width to the back of the wheelchair. Once the child is seated in a stable position, the feet rest appropriately on the footplates of the chair. Finally, a seatbelt should be added at approximately a 45-degree angle to the thighs. With only this little added support these children often find an increase in their hand function and sitting tolerance. The addition of a tray completes this simple seating system.

The Child with Moderate Physical Involvement

The child with moderate physical involvement has greater difficulty maintaining a seated position in a standard wheelchair. Such children have fair head control, but have difficulty maintaining their head in the midline position. Poor trunk control often leads to the early development of scoliotic curves. Because the standard wheelchair fails to provide proper support, the children are often uncomfortable, flopping sideways, or sliding forward out of their chairs and sitting on their sacrums. In this posture, it is almost impossible for them to be comfortable or to perform any fine motor tasks with their hands. Children of this more involved group can benefit even more from an insert placed in a commercially available wheelchair or other wheeled base appropriate to the size of the child.

For the moderately involved child who needs slightly more support, the molded plastic insert (MPI) has been developed ( Figure 3 ). This is a system of standardized seating components fabricated of 6-mm (1/4-in.) or 5-mm (3/16-in.) ABS plastic. We feel that stable midline positioning of the pelvis is the first essential step in proper seating. Therefore, the seat is of the roll-seat design, higher in front than in back, which helps to reduce adductor spasticity and hold the child well back in the chair. There are side panels on the seat portion to hold the pelvis securely in the midline position. Once the pelvis is secure, attention is directed to supporting the trunk.

The back insert is also vacuum-formed of ABS plastic and is contoured to help centralize the child's trunk. Anterior shoulder restraints are added when indicated. A variety of head and neck supports is available. In most cases a simple, soft foam neckpiece is added to keep the child's head away from any hard surface. This protection discourages the strengthening of any extensor tone. Lap belts are always used. Also, these children often require a chest strap to hold them well back in the chair. Feet can be held in proper position by plastic foot receptacles attached to the footplates of the wheelchair. In wheeled bases other than conventional wheelchairs, removable footrests are attached to the seat interface. Finally, a lap tray is added if there is any potential for the child to use his hands, or if it will further help to centralize the child in the seat.

The Severely Physically Involved Child

Many of the children referred to the University of Tennessee Rehabilitation Engineering Center have severe physical involvement. For these children, commercially available wheelchairs are totally inadequate seating devices. Such children have poor head and trunk control, often accompanied by structural spinal deformities and either a high degree of hypertonicity or extreme floppy postures. These children have almost no potential for self-propulsion, since they have very little functional use of their hands.

For the severely involved child a totally different approach to seating is required. Traditionally, seating for these children has consisted of custom-made foam inserts that fit into standard wheelchairs or other specially designed wheeled bases. The amount of customization provided is related both to the degree of total body support required and the fabrication capabilities of the seating technician, orthotist, or therapist responsible for specialized seating. Because each seat must be individually customized, the cost is usually high and, as a result, such services are generally available only through a few larger rehabilitation facilities that have sufficient volume and funding to justify the specialized staff required.

Two other slightly more sophisticated approaches have hecn used in an attempt to provide custom-fitted seating components. One approach follows the process used in prosthetics and orthotics which begins with a plaster wrap of the appropriate body segment, followed by the preparation of a positive plaster mold. Over the prepared plaster mold a plastic-laminate or a plastic vacuum-formed seat or back component can then be fabricated. Another approach has attempted to simplify the above technique by obtaining the body shape using the dilatancy-casting technique. With this technique the patient is positioned on a large bag filled with polystyrene beads. Evacuation of the air from the bag will cause it to become rigid so that the molded bag can then be used as the receptacle to make the plaster mold. Final fabrication of the seat or back follows the steps outlined in the previous approach.

Both of these approaches are very time consuming and result in large, complex mold shapes which usually present difficulty in forming a final plastic seating component. A considerable degree of technical skill is required to obtain a good positive plaster mold of the body shape. Additional skills are required to fabricate the final plastic product, since specialized techniques involving either thermal-forming or thermal-setting plastics are normally used.

The high cost and technical complexity presented by all these fabrication techniques stimulated the staff of the University of Tennessee Rehabilitation Engineering Center to adopt a new approach to seating the severely involved child. The approach, termed the Foam-In-Place (FIP) technique, has been successfully used with 12 children. The FIP technique permits direct foaming of seating components using the patient as the mold. In this manner the mold taking, mold making, and final fabrication steps associated with the previous approaches are bypassed*, In the FIP approach, two-part polyurethane foam** is injected into a mold which consists of a polyethylene plastic box with a thin sheet of latex pulled over the open side into which the patient is positioned. The chemical reaction between the two liquid plastic components produces a foam which forces the latex-sheet barrier upward and around the patient. The foam reaches a gel state within ten minutes. The foam component can then he removed from the mold, covered with a pull-over two-way-stretch fabric, and mounted into a wheeled base. Seat and back components are fabricated separately, allowing adjustment of the seat/back angle ( Figure 4 , Figure 5 , and Figure 6 ).

Our experience with the FIP technique is still limited. Questions such as adequate pressure distribution, heat dispersal, and material durability remain to be answered. However, initial efforts at quickly providing a custom-contoured and comfortable seating system for severely handicapped children by using the FIP procedure are most encouraging.

Conclusions

Over the past three years we have provided at least 200 children with seating systems of the various types described. A multidisciplinary Rehahilitation Engineering Clinic is held twice monthly to evaluate the technical needs of physically impaired children. Once a prescription has been written for a seating system, the child is seen again for appropriate measurements, fitting sessions, and finally in a training session if required. The child is seen again after a two-month interval as part of a standard follow-up procedure.

A formal evaluation has been initiated for the Molded Plastic Insert system. Six centers in the United States will he receiving measuring chairs and components to lit local children with the MPI system. Feedback from this evaluation will permit design refinement, followed by encouragement of the production and distribution process.

The FIP system is still being evaluated locally. Within the next year we hope to have it out on a field evaluation as well.

In conclusion, we would like to stress that a secure and therapeutically designed seating system is often a prerequisite to many other functional activities in which the cerebral-palsied child may participate. The approach described here is the direction taken by one center with a full complement of technical resources. However, a great deal can be accomplished by an enthusiastic staff using basic materials and limited equipment, provided attention is given to the basic principles of seating as outlined above. We suggest that interested institutions begin their programs with the minimally involved child, using the equipment and supplies that are available in most rehabilitation or orthotic facilities. Based on this experience, one can then move forward to the more complex seating challenges associated with the moderately and severely involved child. Experience combined with positive results is the best way to demonstrate that proper seating is possible and is essential to the modern management of the cerebral-palsied child.