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

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 degrees and 87.1 degrees, and .52 and .45 sec (p < or = .0001). The forces on the ATD's occiput were 12,280 and 21,118N in the L and UL conditions, respectively, and lasted approximately 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.