Wheelchair stability and maneuverability: effect of varying the horizontal and vertical position of a rear-antitip device.

Although properly adjusted rear-antitip devices on wheelchairs prevent rear-tipping accidents, many wheelchair users do not use them because they limit manueverability. This study evaluated the use and effectiveness of antitip devices, particularly the effect of the devices' position on rear stability and maneuverability. In an epidemiologic study of the use of antitip devices, using a database of noninstitutionalized users of manually propelled chairs, we found no significant difference in the incidence or nature of rear-tipping accidents between the 167 who used antitip devices and the 399 who did not. We also evaluated seven common manually propelled wheelchairs, occupied by an anthropomorphic test dummy, with and without antitip devices. The added stability provided by the antitip devices varied considerably (from -1.0 to 27.1 degrees) depending on the type of chair, the configuration of the chair and the position of the antitip device. A representative wheelchair was then equipped with an adjustable antitip device that allowed us to test 68 combinations of vertical and horizontal positions. The relationships between the position of the antitip device and both the measured rear-stability and maneuverability values could be expressed by significant regression equations, and correlated highly with the values predicted by a theoretical model that we developed. These relationships should assist clinicians, users and wheelchair designers in finding appropriate compromises between safety and maneuverability.