WHEELCHAIR SAFETY - EFFECT OF LOCKING OR GRASPING THE REAR WHEELS DURING A REAR TIP

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: Bef ore-after trial. Setting: Kinesiologic laboratory. Participants: Ten n ondisabled adults, a sample of convenience. Intervention: In a single representative wheelchair, subjects were dropped from beyond their bal ance points onto a mat with the rear wheels locked (L), with two hands grasping the rear wheels (TH), and with the wheels unlocked (UL). Mai n Outcome Measures: From videorecordings, the horizontal displacement of the rear wheels, the rotation of the rear wheels, and the fall time s were derived. Using an anthropomorphic test dummy (ATD) and a Kistle r force platform, the impacts of the head with the floor were also rec orded. Results: In both the L and TH conditions, the rear wheels moved and rotated backwards. The UL condition was significantly different t han 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 degrees and 87.1 degrees, and .52 and .45 sec (p less than or equal to.0001). The forces on the ATD's occiput were 12,2 80 and 21,118N in the L and UL conditions, respectively, and lasted si milar to 20msec. Conclusion: Locking or grasping the rear wheels has a profound effect on the nature of rear-tipping incidents, a finding wi th important implications for the training of users in how to fall saf ely. (C) 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.