Preventing occupied wheelchairs from falling down stairs.

The hypothesis was tested that wheelchairs could be prevented from accidentally falling down stairs. A rigid post was attached to the wheelchair frame immediately behind the caster (clearance of 13 mm) such that it would strike the floor just after the casters dropped off an edge. The device was tested by means of a 3-degree ramp at the lower end of which was a level surface that ended with a 11-cm vertical drop. Twenty able-bodied subjects descended the ramp, by gravity alone, from progressively greater distances up the ramp, to determine the threshold at which the speed of the occupied wheelchair (with and without the device in place) was sufficient to induce a forward tip down the step. Forward tips occurred at a mean (+/- 1 SD) threshold speed of 0.77 (+/- 0.06) m/s with the device and at 0.38 (+/- 0.04) m/s without it, a mean difference of 0.39 (+/- 0.07) m/s (p less than 0.0005). This preliminary study suggests that such a wheelchair feature might improve the safety of wheelchairs in conditions involving inadvertent loss of caster support, as when they drop off a stair or ledge.