Wheelchair safety: Effect of locking or grasping the rear wheels during a rear tip

Abstract

Objective: To test the hypothesis that, with the wheels locked (by the mechanical locks or by the user grasping the wheels), the rear wheels and the chair rotate slowly backwards during a fall, whereas with the wheels unlocked, the rear wheels rotate quickly forwards. Design: Before-after trial. Setting: Kinesiologic laboratory. Participants: Ten nondisabled adults, a sample of convenience. Intervention: In a single representative wheelchair, subjects were dropped from beyond their balance points onto a mat with the rear wheels locked (L), with two hands grasping the rear wheels (TH), and with the wheels unlocked (UL). Main Outcome Measures: From videorecordings, the horizontal displacement of the rear wheels, the rotation of the rear wheels, and the fall times were derived. Using an anthropomorphic test dummy (ATD) and a Kistler force platform, the impacts of the head with the floor were also recorded. Results: In both the L and TH conditions, the rear wheels moved and rotated backwards. The UL condition was significantly different than the L and TH conditions, with the rear wheels moving and rotating forwards and the fall occurring more quickly, with mean differences of 442 and 455mm, 84.0° and 87.1°, and .52 and .45 sec ( p ⩽ .0001). The forces on the ATD's occiput were 12,280 and 21,118N in the L and UL conditions, respectively, and lasted ∼20msec. Conclusion: Locking or grasping the rear wheels has a profound effect on the nature of rear-tipping incidents, a finding with important implications for the training of users in how to fall safely.