Car Safety Features
Since the arrival of airbags as a safety-device, reports of trauma (especially forearm fractures) have been documented in the literature. This current article1 reports on a 54-year-old woman with osteoporosis who suffered a forearm fracture when her airbag deployed. Her osteoporosis was a risk factor since bone strength is significantly associated with the risk of airbag-induced forearm fractures.
The patient was turning left with her right forearm across the airbag module door. She suffered a “reverse Colles’s fracture of the right distal radius and a nondisplaced fracture of the right ulna styloid process.” Her fractures healed uneventfully.
The patient had widespread osteoporosis in her forearm, hip, and spine; the affected areas also exhibited low density. The authors conclude:
“To our knowledge, the bone mineral density of a patient sustaining an airbag-mediated upper-extremity fracture had not been reported previously. Low bone mineral density and the resulting reduction in bone strength may make patients with osteoporosis more likely to sustain fractures from airbag deployment. Such injuries will become more common as the prevalence of airbags in the vehicle fleet increases. The laboratory data suggest that the range of airbag aggressivities overlaps the population fracture tolerance, so that the occurrence of an airbag-induced forearm fracture may be an indicator of low bone strength.” 2
They suggest that physicians check bone mineral density in postmenopausal women who suffer arm fracture from airbags, and treat with estrogens or other antiresorptive agents to reduce future fractures.
- Huebner C, Reed M. Airbag-induced fracture in a patient with osteoporosis. The Journal of Trauma: Injury, Infection, and Critical Care 1998; 45(2): 416-418.
- Hardy WN, Schneider LW, Reed MP, et al. Biomechanical investigation of airbag-induced upper-extremity injuries. Technical paper 973325. In: Proceedings of the 41st Stapp Car Crash Conference. Warrendale, Pa: Society of Automotive Engineers, 1997: 131-150.
Antilock Brakes and Rear End Collisions
This study examined police records from 1992 and 1993 for five states, looking specifically at rear end collsions. The authors found that cars with antilock brakes (ABS) are significantly less likely to rear-end another car. However, cars with ABS are 30% more likely to be rear-ended themselves!
The authors write, “In order to reap the full safety benefits of the greater braking capability of ABS, drivers of ABS-equipped vehicles need to be even more sensitive than average drivers to the risks of being tailgated. Even though the following driver is presumed to be legally liable, and in many jurisdictions also financially liable, the lead driver nonetheless has many techniques available to reduce, or indeed essentially eliminate, the risk of being rear impacted. These techniques generally require frequent use of rear-view mirrors, which is in general a good driving practice.”
Evans L, Gerrish PH. Antilock brakes and risk of front and rear impact in two-vehicle crashes. Accident Analysis and Prevention 1996;28(3):315-323.
Car Seat Design and Whiplash
A team of Volvo researchers assessed the risk factors influencing whiplash-related injuries, and prepared guidelines for improving car seat and neck restraint design as a means to decrease injury. They stress risk factors are both design- (seating position, and restraint use) and occupant- (gender, height, rear or front seat occupant) related.
After taking into consideration the differing theories of injury mechanisms, the researchers developed the following guidelines for future design:
- Reduce occupant acceleration.
- Minimize relative movements between adjacent vertebrae and in the occipital joint, i.e. the curvature of the spine shall change as little as possible during the crash.
- Minimize the forward rebound into the seat belt.
They explain that the reduction of acceleration is just a basic assumption—if a zero acceleration is achieved, no injury will result. Keeping the spine as evenly supported and intact as possible will avoid injuries, and since seatbelt interaction has been suggested as injury-producing, they aspire to reduce the rebound after impact.
In applying these guidelines in a practical design form, the researchers imply the seatback and head restraint should geometrically support the curvature of the back and neck—this can be achieved by positioning the structures as close as possible to the occupant. Also, no structure in the seat should force the spine into a localized bending position; the seat should follow the shape of the occupant well and properly. Finally, they suggest the implementation of good energy absorption of the seat backrest. The authors explain, “In other words, designing the seat towards lower elastic energy build-up during impact will reduce the forward rebound into the belt.”
The researchers than conducted various testing and mathematical simulations, with positive and applicable findings:
“We believe that using this method will result in a new seat design reducing the risk of neck injuries. An important factor, also due to the nature of the biomechanical guidelines, is that no negative consequences will be introduced…In conclusion, the result of the various tests, and the mathematical occupant simulations, show that the new seat design has considerable potential for offering a reduced risk of neck injuries in rear end impacts.”
Lundell B, Jakobsson L, Alfredsson B, Jernstrom C. Guidelines for and the design of a car seat concept for improved protection against neck injuries in rear end car impacts. Society of Automotive Engineers 1998; SAE 980301.