Influence of rotational axis height of back support on horizontal force applied to buttocks in a reclining wheelchair

Background: Studies have not been conducted to investigate the influence of the height of the rotational axis of a wheelchair's back support on the shear force applied to the buttocks during the reclining motion.

Objectives: The purpose of this study was to investigate the influence of the difference in the rotational axis position of back support in the vertical direction on the horizontal force applied to buttocks for preventing decubitus ulcers.

Study design: Repeated measures design.

Methods: The subjects were 13 healthy adult men without leg and/or trunk diseases. The shear force was measured using a force plate. A comfortable sitting posture in the experimental chair was selected for measurement. The rotational axis was positioned 13 cm forward on the horizontal plane from the intersection between the seat and the back support. The axis positions on the vertical plane as two experimental conditions were the seat height and the 7.5-cm upward from the seat height which was nearer to the hip joint.

Results: In returning the back support to an upright position, the horizontal force was 12.4 ± 1.6 (percent body weight) under the seat height-axis condition and 10.1 ± 1.8 (percent body weight) under the upward-axis condition (p < 0.01).

Conclusion: This result suggested that the wheelchair might have to be capable of adjusting the height of the rotational axis of the back support to reduce the horizontal force applied to buttocks.

Clinical relevance: This study shows one of the suggestions regarding seating approach for the prevention of decubitus ulcers. There is a possibility of reducing horizontal force applied to buttocks after reclined back support, by adjusting the height of the rotational axis position of wheelchair back support.