Bucket Seat Orthosis

GREG BELBIN, CO(C) AND JOAN FERGURSON, MCSP, MCP*Toronto, Ontario


At The Hugh MacMillan Medical Centre we follow approximately 600 children and young adults with spina bifida. Several years ago, the need for a seating device for young children with thoracic and thoracolumbar myelomeningocele was identified. Many of these children are unable to develop independent sitting without hand support (Fig. 1 ) and others had delayed sitting development. Sitting problems hampered development of hand skills. In normal developmental sequence, independent sitting with hands free is achieved between the age of 6 to 8 months. Then the child can manipulate toys and explore the environment, facilitating the development of cognitive skills, essential fine motor skills, and sensory discrimination while touching one's own body and different textures in the vicinity. Seating devices available to us were cumbersome and inadequate in providing necessary support. A corner table and chair, for example, can allow hands-free sitting, but does not provide adequate support for many children who must tense their shoulders and extend their necks to stabilize the trunk. Custom seating can be made for the caster cart, star car, high chair and stroller. All provide the necessary support, but their use is restricted to the vehicle or chair for which they were fitted.

The present model of the bucket seat evolved from a type of bath seat which was being fabricated for severely involved children primarily with cerebral palsy. Modifications and refinements to this original design have been made over the years making the device more adaptable to meet the complex needs of individual children.

The bucket seat consists of an inner Plastazote liner, a chest strap or corset, and an outer high-density polyethylene shell and base (Fig. 2 ).

Assessment

The decision to prescribe a bucket seat orthosis is made after a team assessment of the child's needs by an orthopedic surgeon, orthotist, physical therapist, and parents taking into consideration orthopedic and respiratory status, developmental level, and the needs of the family. At this assessment decisions are also made about the child's functional position and corrective measures to be accommodated into the casting, including head support.

Casting and Fitting

A plaster cast of the patient's trunk including the pelvic area is required if a satisfactory fitting is to be achieved. A decision is reached as to the optimum position for casting. Prone is chosen where head support is not required. Supported sitting is used if head control is to be incorporated.

The appropriate size of cotton stockinette is placed over the patient's trunk and extended below the buttocks. Areas of specific concern, such as bony prominences and scoliosis, are outlined with an indelible pencil for future reference. When casting in supported sitting, a second orthotist holds the patient in the desired position (Fig. 3 ).

Standard plaster of paris bandage slabs are applied to the child, beginning with the posterior aspect of the trunk and extending from C7 to the base of the buttocks. Additional plaster is applied to the back and extended anteriorly, to cover two-thirds of the chest and abdomen. Before the plaster sets, both orthotists apply corrective forces to the trunk ensuring the pelvis is level. The head and neck are then incorporated if required, ensuring balance over the trunk. After the cast has hardened, it is easily removed by cutting the anterior aspect of the stockinette with a pair of scissors.

The positive cast, which includes all specific corrective features from the negative mold, is modified slightly by building up plaster over bony prominences. Should the child require one or several three-point pressure systems to control flexible scoliotic and kyphotic curves, plaster can be removed from the cast incorporating these specific pressures in the finished orthosis.

Once modified, the cast is screened until smooth and preparations are made for the vacuum forming of the inner liner and outer shell. Various thicknesses of Plastazote padding can be used depending on the amount of correction required to support the child. Usually a 1 cm ('/z in) thickness is sufficient for maximum comfort and support. The outer shell is vacuum formed on top of the inner liner with 0.5 cm ('/a in) high density polyethylene. This is the ideal material because of its high chemical resistance, durability, and vacuum forming capabilities.

After the plastic has cooled, the outer shell and inner liner are removed from the cast, rough edges are sanded smooth, the chest pad or corset is fabricated, and a proper size base plate to provide stability is cut and fitted to the bucket seat.

During the fitting and finishing of the orthosis, the orthotist assesses the amount of support given to the child's torso and checks for redness over the pressure-sensitive areas. Head position is examined for alignment with the trunk and the legs are judged with respect to internal or external rotation. The aim is to achieve an upright position; however, it may be necessary to recline the bucket seat slightly using wedges between the base plate and the seat. Finally, the chest pad assembly is secured to the bucket seat (Fig. 4 ).

Advantages

The bucket seat can be contoured to minimize the frog-legged position seen in many children with thoracic myelomeningocele, thus aiding in the prevention of contractures.

When completed, the bucket seat:

  1. Must not impair upper arm mobility.
  2. Must fit snugly, but not restrict breathing.
  3. Must support the spine and protect the kyphus.
  4. Must enable hands-free sitting balance.
  5. Must have a stable base of support.
  6. Head support if used, must not impair peripheral vision.

The bucket seat can be transferred from the high chair (Fig. 5 ) to the caster cart (Fig. 6 ) or stroller and is also free standing on the floor.

It is, of course, important for the therapist to work with the child on floor skills and trunk control to develop independent hands-free sitting, if this is at all possible.

The bucket seat is an invaluable piece of equipment. Parents appreciate its versatility and ease of transportation because of its compact size and light weight. It has facilitated for many children the development of hand skills, independent mobility, and for some, independent sitting balance.

*Mr. Belbin is Senior Orthotist; Ms. Fergurson is Senior Therapist at The Hugh MacMillan Medical Centre, 350 Rumsey Road, Toronto, Ontario M4G 1R8