Causes of severe injuries in wheelchair user motor vehicle passengers: pilot study for future safety restraint system.

Abstract

Background: As population aging progresses in Japan, an increasing number of older wheelchair users regularly travel in the rear space of motor vehicles. Poor seatbelt fit is the main cause of severe or fatal injuries in collisions. The current study sought to examine the potential risks regarding seatbelts for wheelchair users in Japan using national statistics, and to elucidate the mechanisms of injuries among wheelchair users involved in frontal collisions using sled tests. We propose a restraint system for wheelchair users traveling in vehicles.

Methods: To identify cases of collisions involving vehicles with wheelchair user passengers, national police database was examined. A sled test representing a 48 km/h frontal collision with a Hybrid III AF05 dummy was used to examine kinematics at collision and biomechanical parameters of wheelchair users. We examined three test conditions (1. generally used seatbelt path for standard wheelchairs; 2. close seatbelt path for standard wheelchair; 3. close seatbelt path for sturdy wheelchair).

Results: According to a national database in Japan, a seatbelt was worn in most cases of fatalities and casualties among wheelchair user passengers. In sled test condition 1, the dummy moved forward and the lap belt compressed the abdomen. High values were observed for head injury criterion and neck injury criterion. In condition 2, the dummy moved forward and fell because the wheelchair seat collapsed. In all conditions, high values for chest deflections (51.3 to 53.8 mm) were caused by high shoulder-belt load (8,217 to 8,660 N).

Conclusions: Indications for future design of safety restraint system were provided as follows: both the shoulder and lap belts would be correctly positioned across the bony parts of the shoulder and pelvis, respectively; a force limiter would be installed in the restraint system to reduce shoulder belt loads; a sturdy wheelchair and adequate tie-down system that can resist applied forces would be used.