DEVELOPMENT OF A USER INTERFACE FOR A TOTAL SUPPORT WHEELED WALKER.

Stephen J. Harvey Bath Institute of Medical Engineering Ltd, Wolfson Centre, Royal United Hospital, Bath BA1 3NG, UK.

ABSTRACT

With devices that involve human interaction, such as walking aids, it is the interface between the user and the device which determines the success of the product. Many walking aids offer only one type of patient interface, often preventing its application to patients who have less straightforward problems. This paper describes the development of a modular interface system to fit a total support wheeled walker for a child with cerebral palsy, providing greater support and postural control.

BACKGROUND

The project was referred by a physiotherapist working closely with a child at a local special needs school. The spastic diplegia cerebral palsy child had severe learning difficulties and behavioural problems. Associated with these disorders the child had a low attention level, little ability to communicate, became tired quickly and was overweight due to lack of activity.

The child's previous mobility was by crawling on hands and knees. This severely affected his interaction with other pupils and his ability to investigate the surrounding environment. Various commercially available walking devices had previously been tested for suitability in providing a supported walking posture for the child, but no single device provided a successful solution.

A multi-skilled project team was formed to address the problem, consisting of physiotherapist, teacher, care assistant and rehabilitation engineer. The team members were consistent throughout.

STATEMENT OF PROBLEM

1. To investigate the possibility of providing a device to assist in achieving an upright walking posture with the long term aim of reaching independent mobility.

2. To ensure the device provides full body support without causing discomfort to the child, or restricting the child's natural gait. The device would need to be used in many different situations, for general mobility, and for interaction with other people and the environment, in addition to being a useful therapy aid. Clearly the patient must feel safe when in the device and should be easily manoeuvred into and out of the device.

RATIONALE

An initial assessment was carried out to see how the child interacted with a standard walking device already manufactured by the Institute. The child was filmed using the device, which provided a suitable record of the child's posture and walking action. This initial recording provided an excellent control for the whole investigation and was constantly referred to by the project team.

It was clear from this assessment that there were numerous and complex factors influencing the patient's ability to interact with the walker, more than could form the basis of a specification for an ideal design. Therefore, a relatively crude interface test rig was designed allowing an evolutionary design principle to be followed where the project team guided the design of the interface depending on the child's interaction with the test rig.

There were some key points which needed to be specifically addressed when developing a design: ease of patient access; improved pelvic and thoracic support; direction of the patient's body weight through his legs; rectification of his natural sitting posture and improvement to child's gait.

The base framework of the standard walking device provided a steady mobile platform for the patient to be positioned in, and coped with the different environments admirably, i.e., narrow doorways, differing contact surfaces, and so on. The real challenge was to develop a more suitable user interface which would provide the desired features mentioned above.

Concept theory

Figure i illustrates the child's posture when positioned in the standard walker. The idea was to change how the child interacted with the device to produce a more desirable posture, as shown in Figure ii. Certain key areas were focused on to assist in achieving the preferable upright position.

Figure i Figure ii

Key areas: To utilise the child's better upper body strength to help control and support a more upright body position.

To position the body slightly forward in an attempt to achieve a more effective walking action and to direct the patients body weight through his legs.

To provide superior pelvic and thoracic support to assist in maintaining balance.

DESIGN AND DEVELOPMENT

Test rig design

As there were so many unknowns, a relatively crude interface test rig was designed incorporating maximum flexibility, so allowing height, angles and orientations of the patient to be adjusted. Figure iii, gives a simplified diagram of the initial test rig assembly.

Figure iii. The test rig design consists of the outer support frame, to which an adjustable thoracic plate is attached. The angle of the plate is adjusted by the supporting link (1), thus changing the angle of the user's upper body. Located centrally at the bottom of the thoracic plate is a pommel. The angle of the pommel is adjusted by link (2) and provides a rigid support for the user. Together, the Pommel and thoracic plate can fully support the user's body in different orientations, but adjusted independently. A safety strap passes around the patient's back and fixes to the angled board.

Evaluation

The child was then assessed in various walking postures within the test frame. The performance and posture of the child were recorded on video during the assessments. Being able to replay the assessments was immensely beneficial when analysing and comparing different interface configurations. The process triggered ideas more easily than merely relying on memory and acted as a superb communication tool within the project team. The 'brain storming' stage of the project could continue away from the patient, thus reducing the assessment time and causing less distress to the patient. All the assessments were carried out with the same members of the project group present. This was to ensure the patient's emotions were consistent throughout, as his behaviour varied with different people.

User trials

When the optimum posture was reached, the configuration/geometry of the test rig was then finalised as a permanent sub-assembly, which attached to the standard walker base. Extensive user trials were then carried out for periods of several weeks at a time. Minor adjustments were made to the structure during these periods to improve the patient's comfort, the ease of positioning him, and refinements to his posture. Each modification to the framework was recorded on video to evaluate any improvement in posture and walking action of the patient. There was an enthusiastic input from the staff members at the School. A logbook was kept on the child's progress, and highlighted areas of difficulty which needed to be addressed. Some of these points were resolved by small alterations to the design. The user trials were continued until no further amendments to the interface were necessary.

RESULTS

The new interface ensured a safe, comfortable, and fully supported upright position for the child to walk independently with. Once a satisfactory posture had been achieved, physiotherapy could begin on improving the child's gait. The child used the device daily for two thirty minute periods and the duration was increased as the child became more capable.

Figure iv.

DISCUSSION

Modular design A modular design approach was adopted, utilising sub-assemblies from the existing standard walker. This specialised interface sub-assembly provided the correct 'user-device' interaction to support the patient in a superior walking posture as compared with any commercially available walking aids. Adopting this common industrial principle for the user interface has basically produced a device which is attractive to different and larger patient groups.

Future work Further patients have been referred requiring a total support walking aid. Another prototype test rig has been developed for a slightly different patient group and is awaiting evaluation. The long term aim is to produce a multi-functional test rig for postural evaluation purposes and from this, possibly, a set of six interface sub-assemblies could be made available to be used with the standard walker base.

Method of evaluation/project approach There is no doubt that there were two factors in the project procedure that heavily influenced the success of the final result.

Firstly, having a multi-skilled project team ensured that all aspects of the child's background, behaviour and ability were appreciated. This achieved a more accurate analysis of all evaluations.

Secondly, being able to record the patient's posture and interaction with the device, on film, was very effective. This saved valuable time during patient evaluations and the design process. It also minimised any disruption of the patient.

CONCLUSIONS

1. A total support walking device has successfully been developed for a child with spastic diplegia cerebral palsy through designing a completely new user interface.

2. Independent upright mobility is now possible for the first time, and allows the child to interact with his surroundings and other people more easily.

3. The modular design diversifies the product suitability for a larger number of patient types.

ACKNOWLEDGEMENTS

The author wishes to thank Liz Ash, phsyiotherapist and the staff at Larkrise School for their advice and enthusiasm, which significantly helped in the development of the successful device.

Stephen Harvey, AMIEE, Design & Development Engineer, Bath Institute of Medical Engineering Ltd, Wolfson Centre, Royal United Hospital, Bath BA1 3NG, UK. Tel. 441225 824103. Fax. 01225 824111. email: bime@bath.ac.uk Wheeled Walker