Moulded supportive seating for the disabled
N. D. Ring *
R. L. Nelham *
F. A. Pearson *
In severe cases of physical disability intimate supportive seating may be required to provide maximum comfort, a good position for functional activities, improved respiration, relief of localized pressure, control of spasm, protection, or improved management. A service for providing such seating has been developed at Chailey Heritage. The seat is vacuum-formed from thermoplastic materials, having a soft non-absorbent foam for the liner and a hard semi-rigid outer shell. A mould is obtained by casting the patient using the vacuum consolidation technique and by recording the resulting impression using plaster-of-Paris. Nearly 200 seats have been made using the technique with a high rate of success.
The importance of seating
Good seating contributes significantly to enjoyment and functional daily living for both the disabled and the able bodied. Most people spend several hours each day sitting, whether for eating meals, watching television or as part of their jobs. For the disabled the period may begin as soon as they are dressed in the morning and continue late into the evening, a period of perhaps 12-16 hours.
Despite this long and intimate contact people frequently accept very poor quality seating. Observations once made in a furniture store revealed that, on average, people spend less than one minute sitting in a chair to test it for suitability before making a purchase. All too often a similar uncritical approach is applied to the disabled by those responsible for specifying a pan;icular seating arrangement.
What is the purpose of a seat ?
Normally a seat can be specified from two considerations; firstly its function and secondly its relationship to the body tissues and anatomy. Functionally, the specification is usually clear, alternatives being for such purposes as relaxation, manual tasks, vehicle control, and so on. The critical features in a seat's relationship to the body are, however, less clear and may include both comfort and stability of the total body as well as distribution of pressure, skeletal support and protection of individual parts. All contribute to an improved quality of life.
Partial solutions to satisfy these criteria may be sought through a variety of approaches (Chailey Heritage, 1977). The simplest is by using a cushion, or by interposing, say, a sheet of lambswool between the seat and the patient. These help to distribute pressure and reduce shear forces within the tissues. Lambswool is also able to absorb perspiration, thus increasing comfort. More support can be achieved by using wedge shaped cushions in standard sizes or shaped to suit the individual. If even further support is required it may be provided by using a modular system, such as that produced by Trefler et al. (1977), in which vacuum moulded components can be combined in a variety of ways to build up an appropriate seat. Finally, if none of these approaches prove satisfactory, an intimate personalized seat shell, such as that produced at Chailey Heritage (Fig. 1 ), must be used (Nelham, 1975). In such a shell the whole seat is accurately contoured to the individual patient in order to provide support, relief and protection, as appropriate, over the whole seating surface.
Whichever seating system is used, it is important that the user shifts or relieves his weight at regular intervals. In the cases where seat shells are used this may require the assistance of an attendant. For many patients complete removal from the seat shell is necessary, say, every two hours.
In considering the provision of a moulded seat, it is important to be mindful both of the positive features and also of the limitations of such a piece of equipment. The seat will satisfy only certain criteria and care must be exercised to ensure that the medical requirements and the patient's personal desires can be accommodated within these criteria. The features offered by the seat shell system at Chailey are as follows :
Pressure distribution. By being accurately moulded to the body, the seat provides support over a large area and localized pressures are significantly reduced.
Postural support. The intimacy of fit gives good postural support which may be extended to include the head. However, the seat will provide little or no correction and where significant correction is needed an orthotic or other approach must be used.
Improved respiration. Improved postural support frequently produces improved respiration. This is especially true with cases of muscular dystrophy.
Spasm control. By holding the patient in a good postural position, spasm can frequently be reduced, largely, it is felt, because the patient is able to relax in a good position.
Protection. The construction of the shell, which combines a washable foam liner with a semi-rigid backing, provides good protection for such conditions as osteogenesis imperfecta or severe kyphosis.
Improved management. For transport the seat shell provides excellent support and improves safety in both a wheelchair and a car or other motorized transport. Further, for general nursing management, the seat can be used in a variety of ways. Some have found that it is easier to carry children in the seat. Also on the toilet an unlined seat (with a suitable hole) allows a patient to be independent of constant supervision.
Increased independence. In addition to the example cited above, greater independence may be achieved for, say, self-propulsion of a wheelchair.
The clinic and clinical considerations
The team, which is led by a clinician, includes a physiotherapist and occupational therapist and appropriate members of the rehabilitation engineering staff. Not all members are always present since frequently a child is escorted by a therapist or mother, under which circumstances one of the therapists from the team may not be required.
In organizing the clinic, emphasis is placed on the need for sufficient time to be available. The type of case seen has frequently been referred for this variety of seat as a "last resort" and two to five hours in the clinic may be required to ensure that the final seat will prove satisfactory.
Experience at Chailey has centred round four disabilities: cerebral palsy, spina bifida, muscular dystrophy and osteogenesis imperfecta. Scoliosis has been present in a high proportion of these cases. The best that can be achieved for the treatment of the scoliosis is to afford support by careful moulding over the prominent rib curve and the contralateral pelvis in the hope of holding the scoliosis or retarding deterioration.
Certain principles and techniques related to specific disabilities have been developed. For cerebral palsy a comfortable posture is sought to encoµrage relaxation and the attitude of the seat may be determined by function. In spastic cases a pommel is often incorporated to maintain abduction of the hips, which may also be held in a small amount of flexion to encourage relaxation. This can, however, be contra-indicated on other grounds, for example urine drainage, and such flexion should be carefully assessed.
The muscular dystrophy case is often floppy and difficult to handle. All round support is indicated with careful moulding in the small of the back to encourage extension of the upper spine, thus facilitating respiration. A pommel may be desirable, but should be considered in conjunction with toilet requirements since such cases may need to use a urine bottle while seated.
Osteogenesis imperfecta is less common than the above groups. The main consideration is protection and for this purpose the seat is not so closely contoured to allow freedom of movement while reducing the risk of accidental impact.
Assessment and casting of patient
The most important stages in the provision of a seat are the assessment and casting procedures. In assessing the patient, both medical consideration, as above, and functional consideration are vital, such as the type of usage (for example, at home or at school), any particular situations of usage (such as, in a car), cosmesis, and so on. Once an assessment has been performed and indications for a seat agreed, the casting procedure is carried out. Clearly, this represents the foundation for ultimate success, and sufficient time must be allowed to achieve this.
The technique used is based on vacuum consolidation, which has been widely reported elsewhere (Fitzgerald et al., 1965; Nichols et al., 1971 ; Germans et al., 1975). Modifications to the technique have been introduced and it is now based on purpose designed latex bags which are filled with small (2 mm diameter) expanded polystyrene beads. Each bag, or compartment, can be independently evacuated and sealed to maintain a posture. Thus, once an impression has been taken of the patient he can try out the attitude and other features of the seat over an extended period in order to ensure the seat shape will provide the support and permit functional activity according to the team's recommendations.
The impression is normally recorded using plaster-of-Paris bandage. This produces a cast which, with a minimal amount of rectification, is suitable as a mould for vacuum forming. Rectification is carried out in three steps. First, a "skirt" is added to the cast, when inverted, to ensure it sits firmly on the forming table. Second, a thin cream of liquid plaster is spread over the working surface of the cast to fill any small irregularities in the surface. Third, the cast is strengthened inside with a build-up of liquid plaster to a thickness of about 20 mm to prevent the cast collapsing under vacuum.
Manufacture of seat
The seat is manufactured using a vacuum-forming machine capable of moulding plastic up to 1 metre square. The maximum depth of draw is 700 mm and the heater layout allows both top and bottom heaters to be controlled in appropriate zones.
The materials used are 15 or 18 mm Evazote (Ethylene Vyoyl Acetate foam) and 5.5 mm ABS (Acrylonitrile-Butadiene-Styrene). The Evazote is a soft closed-cell foam which provides a comfortable liner for the seat and is able to accommodate small irregularities, such as creases in clothing. The seat is constructed by first forming a layer of Evazote over the cast and then a layer of ABS over the Evazote.
In this condition the seat is prepared for a trial fitting by roughly trimming the excess plastic. At the fitting stage the correct attitude for the final seat is recorded, a trim-line is marked and the positions of any harnessing identified (Fig. 2 ). This fitting is also used to check the detail of the fit and, if necessary, small changes can be made by using a hot-air gun. As soon as the seat has been trimmed the patient sits in the seat for several hours, if possible, to ensure correctness of fit and maximum comfort.
Once the team is satisfied that all is as required manufacture of the seat is completed. This involves locating a circular base on the shell and forming another layer of ABS over the whole seat (Fig. 3 ). When this layer has been trimmed to the final trim-line the seat is edged with a commercial edging strip and fitted with a suitable harness (Fig. 4 ).
Logistics of service
The provision of a seat of this type almost inevitably indicates that the patient is severely handicapped. Thus, speed of supply is considered extremely important to prevent deterioration of the individual's condition. Normally a child is seen three weeks after the initial referral is received and he is then admitted, with his parents or escort, to a self-catering bungalow. Assuming that no complications occur, it is possible to deliver the seat on the same day as the child is first assessed. However, for practical reasons, manufacture is more reliably carried out over a three-day period, and the service has been developed according to this pattern.
Up to September, 1977, 180 seats had been produced, 108 through the Chailey clinic and 72 on casts produced at the Wolfson Centre in London. Regrettably it has not been possible to carry out the detailed follow-up which is clearly desirable. However, a questionnaire survey was carried out in December, 1976, of both the parents and the referring medical practitioner in 53 cases in order to obtain some impression of the seating system both in terms of its acceptability and to identify any clear disadvantages. There was an 80 per cent return and the answers are summarized in Table I. Clearly, these results lack the specificity which one would desire and it is intended to launch a follow-up early in 1978 by visiting children in the user situation. However, the results obtained from such an encouragingly high return do, at least, give reason for cautious optimism.
Refitting of the seats has to be performed to allow for growth and, on occasion, deterioration. The period between refits is, of course, extremely variable but tends to be 9-12 months.
The seating system described has been developed since 1973 and has had wide clinical exposure. The seats clearly perform a valuable function provided they are supplied to match the criteria stated. The success of the service centres around three features, namely the rapid supply, the method of manufacture and the close team work. For this success, the authors would like to record their gratitude to all who have been involved in the development, particularly to Jill Rockey, Kim Barton and Steve Mottram, without whose expertise the programme would not exist.
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Nichols, P. J. R. and Strange T. V. (1971). A method of casting severely deformed and disabled patients. Rheum. Phys. Med., 11: 7, 356.
Trefler, E., Huggins, -, Hobson, D., Hanks. -, and Chiarizzio (1977). A modular seating system for physically handicapped children. Conference on Systems and Devices for the Disabled. University of Washington School of Medicine.