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A COMPLIANT SEATING SYSTEM FOR A CHILD WITH EXTENSOR SPASMS.

Dr Roger Orpwood. Bath Institute of Medical Engineering, Wolfson Centre, Royal United Hospital, Bath BA1 3NG. UK

ABSTRACT

A child with severe extensor spasms was very difficult to seat because of his movements. He was extremely uncomfortable in a rigid seating system and any constraint to his movements made him extend even harder. A seating system is described which has moveable support surfaces that are connected to a sprung linkage mechanism. This construction allows the child's extensor movements to take place, and then gently returns him to a stable position. The same philosophy was used for other restraining components such as shoulder straps by using elasticated neoprene fabric.

BACKGROUND

A number of children have presented with severe extensor spasms involving their whole body that make it very difficult to seat them comfortably. Even with carefully customised seating they are only comfortable in their relaxed state. As soon as they try to extend they push against the seating surfaces and cause themselves much pain. In addition, the mere fact that the support surfaces form an immovable barrier to their movements seems to make them extend all the harder. Such children are often only comfortable when they are sat on a carers lap. In this situation the carer will allow the child to move when he extends. When the child relaxes the carer will gently encourage the child back to a stable position again. This paper describes a seating system that was developed for an individual child to help in this situation by emulating the movements of the carer.

OBJECTIVES

An alternative form of seating is needed which behaves more like the carer and moves with the child. The support surfaces need to articulate relative to each other, following the child's movements, and providing a gentle returning force which encourages the child back to stable position when he relaxes. This compliance needs to be provided whilst maintaining the security of the child.

APPROACH

A compliant seating system. The child for whom the initial device was developed was most comfortable when he had his legs folded up into a tight 'Z'shape. When he extended he articulated about his hips, pushing back with his upper body, and pushing forward with his thighs. A seating system was designed that provided support surfaces that initially held him in this favoured relaxed position. However the surfaces were hinged relative to each other so that the back surface could hinge backwards and the thigh board could hinge forward. These movements were linked via a four-bar linkage mechanism and the mechanism contained an adjustable spring. The spring held the support surfaces against stops. In this way the normal position of the seat was the child's favoured position, and there was some initial resistance to movement dependant on the resting extension of the spring as it was held against the stops. When the child extended, the support surfaces moved with him; when he relaxed, the spring loaded mechanism gently returned him back to his stable position again. The spring tension and the position of the stops could be adjusted.

RESULTS

The seat was extremely well received by the child. His initial reaction was one of feeling a little insecure because of the seats movement but he became reassured within a matter of minutes. After that, and for the first time for several years, he was able to sit comfortably on his own. Anecdotally the severity of his spasms were also reduced after a few weeks use of the chair.

DISCUSSION

We found that the tension in the spring and the way the tension changed with the movement of the support surfaces was quite critical for the child. Too low a tension and the spring could not return him to a stable position. Too high and the resistance provided had the same effect as the rigid supports and encouraged the spasm. It was important to have adjustment of the tension to help tailor the seat to the individual. As with all work requiring development to suit the needs of an individual, the use of video recordings kept a good record of progress and also provided an invaluable tool to help the engineer make appropriate changes to the design.

A second seat was made for the same child to fit onto a wheelchair base. In the second seat gas struts were used to provide the return force but these proved to be unsatisfactory. It appeared that the intrinsic damping of the gas struts had some impact on the "feel" of the seat for the child. This exercise underlined the importance of the

A compliant seating system. subjective reaction of the child to the movements that took place. Any excessive reaction on the part of the support surfaces to the child's movements seemed to provide feedback which exacerbated the reflex contractions

The technique of using compliant supports was extended to the child's arms. Independently to his whole body movements he tended to contract his arms up into his face, often causing injury. Rigid arm restraints again caused him pain because the very rigidity of the constraint made him contract all the more. Arm supports were therefore constructed from neoprene fabric, the sort of material used for wetsuits. The strong elasticity of this material was ideal in providing a restraint but at the same time providing some compliance to initially allow arm movements but then to return them to a resting position.

The neoprene has proved to be valuable in other ways. The child often had smaller independent spasms where his shoulders would bilaterally extend forward. It was found that restraining straps over his shoulders to keep his upper body stable were again very uncomfortable unless they were constructed from the neoprene fabric. The neoprene allowed some movement of his shoulders but, as with the arm supports, they pulled him back to a stable position when he relaxed.

It is felt that the approach used with this child of providing compliant support surfaces and constraints serves to reduce extensor spams through allowing some movement, and to make the child very much more comfortable.

ACKNOWLEDGEMENTS

The author wishes to thank of the staff of Critchill School, Frome for their help in developing the seating system, to Alison Rouse and Tessa Hyde for Occupational Therapy support, and to Martin Rouse for his technical skills and dedication.

Dr Roger Orpwood Bath Institute of Medical Engineering, The Wolfson Centre, Royal United Hospital, Bath BA1 3NG. UK. Tel. 01225-824103 Fax. 01225-824111 email. bime@bath.ac.uk