Assessment of forces imparted on seating systems by children with special needs during daily living activities

The principle of wheelchair seating systems for children with special needs and particularly children with cerebral palsy is to maintain body posture, balance, stability and comfort, while allowing the user to participate in activities of daily life. However, the problematic nature of involuntary movement in children with spastic cerebral palsy causes difficulty with chair interfacing and positioning. Furthermore the high impact forces suddenly produced result in high contact forces that potentially cause pain and injury, which also impair their functional abilities. During an extensor spasm, the impact forces experienced by the user on conventional rigid systems may be reduced with the use of a wheelchair with dynamic response. The dynamic backrest system permits forward and backward movement as the occupant extends and retracts his or her body. In the expectation that it will respond appropriately to children with strong muscle spasms, through reducing the pain and pressure from restricted posture, while still providing the appropriate support. However, the quantitative effectiveness and impact of using dynamic components has yet to be established. Therefore our objective is to quantify and compare the imparted forces on equivalent rigid and dynamic seating systems, to understand the interactions between force, wheelchair compliance and physical activity throughout a four hour session of non-laboratory based daily living. The Mygo™ seating system which was used for this study was fitted with strain gauges. It has been designed to capture load data, with one hundred strain gauges arranged on certain components in such a way that each strain gauge bridge was sensitive to a particular direction. The fully independent data acquisition system was located in the base of the wheelchair facilitating mobility. Therefore the subject was able to perform their activities of daily living normally without interruption, before being returned to their normal chair at the end of the agreed time.