Low anterior counterweights to improve static rear stability of occupied wheelchairs.

Rear tipping accidents in wheelchairs are a common problem, the likelihood of which may be increased by the combination of a wheelchair with low stability and an occupant with altered body morphology, such as a person with lower limb amputations. This study tests the hypothesis that counterweights on the wheelchair footrests significantly increase static rear stability. In addition to pilot work indicating the amount and positioning of effective counterweights, ten normal subjects were studied on a tilting platform in both lightweight and conventional wheelchairs, with and without a 5-kg weight on the footrests. The angles at which the front casters lifted off the platform increased from a mean of 28.6 (+/- 2.7) degrees to 34.8 (+/- 3) degrees in the conventional wheelchair (p less than 0.01) and from 18.2 (+/- 2.7) degrees to 24.6 (+/- 2.5) degrees (p less than 0.0001) and 15.5 (+/- 2) degrees to 23.4 (+/- 2.2) degrees (p less than 0.0001) in the lightweight chair with the axle in the low-posterior and low-anterior positions, respectively. A 5-kg weight on the footrests increased the average rear stability of lightweight and conventional chairs by 6.2 degrees (31.9%).