Hearing loss and automobile airbag deployments

In an on-going research program, on the causation of injuries in motor vehicle accidents, at the University of Michigan Transportation Research Institute, crashes with airbags have been, and are continuing to be, investigated. In order to determine the occurrence, if any, of 'hearing problems' associated with airbag deployments, drivers and passengers who had been involved in 'airbag' automobile crashes were interviewed by telephone. From the crashes investigated, 225 attempts were made to contact drivers who were exposed to airbag deployments. From these telephone interviews, contacts were made with 177 car occupants. Only three reported that they had experienced any type of hearing-related problems subsequent to their crash. One other case is reported of a driver who had pre-crash hearing loss. It appears that permanent hearing deficit due to airbag deployment, both in cars with the steering wheel airbag alone, and in those with a passenger side airbag, is an infrequent event (1.7%) from the data of this study.

Air bags: an update

Overwhelming evidence shows that air bags save lives and reduce morbidity associated with MVCs. The resulting benefits far outweigh the risks of air bag injury or death. Emergency nurses play a pivotal role in educating the public about active seat belt use in conjunction with passive restraint systems such as air bags. Air bags cannot be viewed as a single solution or panacea to occupant protection. Air bags are designed as supplemental devices to be used with seat belts and require the active participation of the user for maximum benefit and safety.

The effects of seat belts on injury severity of front and rear seat occupants in the same frontal crash

Data on passenger cars in frontal crashes were reviewed using NASS 1980-1991. Only crashes with one or more rear seat passengers were included. Combinations (pairs) were made based on restraint use: lap-shoulder belts in the front seat (or no belts worn) and lap belts, (or belts worn) in the rear seat. Passive belts or child restrained occupants were not included. The AIS was used for injury severity. The data indicate the rear seat to be a safer environment. Lap belted rear seat occupants always fared better than their front seat counterparts.

Upper extremity injuries related to airbag deployments

OBJECTIVE

Details on airbag injuries to the upper extremity are relatively unknown to clinicians. The injuries presented here should provide a clear understanding of the mechanisms of forearm, hand, and wrist injuries that may be seen by emergency room physicians.

MATERIALS AND METHODS

From our crash investigations of 325 airbag-equipped passenger cars, a subset of upper extremity injuries are presented that are related to airbag deployments.

MAIN RESULTS

Minor hand, wrist, or forearm injuries--contusions, abrasions, and sprains--are not uncommonly reported. Infrequently, hand fractures have been sustained and, in isolated cases, fractures of the forearm bones or of the thumb, wrist, and fingers. The close proximity of the forearm to the airbag module door is related to most of the fractures identified. Steering wheel airbag deployments can fling the hand-forearm into the instrument panel, rearview mirror, or windshield, as indicated by contact scuffs, tissue debris, or the star burst (spider web) pattern of windshield breakage in fron of the steering wheel.

CONCLUSION

Minor injuries of the upper extremity can occur when contacted by the deploying airbag either directly or by flinging the hand-forearm into interior car structures. Fractures of the forearm are rare and usually are due to direct impact by the forceful opening of the airbag module door.

Vertebral column injuries and lap-shoulder belts

OBJECTIVE

To present cases of vertebral column fractures or fracture dislocations that occur to restrained front seat occupants where there is no evidence of body contact with interior car components based on both medical records and car inspection.

MATERIALS AND METHODS

Reviewed were car crash injury cases investigated at the University of Michigan Transportation Research Institute and at the University of Birmingham (England) as well as the National Accident Severity Study files of the National Highway Traffic Safety Administration. Medical records and car inspections in the cases presented did not indicate any evidence of body contact with interior car structures.

MAIN RESULTS

Vertebral fractures or fracture dislocations sustained by front seat occupants who were wearing lap-shoulder belts are rare, as evidenced by the relatively few cases identified in the literature and in the crash injury files reviewed.

CONCLUSIONS

Infrequently, in frontal crashes, vertebral fractures or fracture dislocations can occur to lap-shoulder belted front seat car occupants without head or torso impacts with interior car structures. Cervical spine injuries are due to neck flexion over the shoulder portion of the restraint. Thoracolumbar fractures can occur in the frontal crash even at low crash velocity.

A review of cervical fractures and fracture-dislocations without head impacts sustained by restrained occupants

Crash injury reduction via lap-shoulder belt use has been well documented. Like any other interior car component, lap-shoulder belts may be related to injury in certain crashes. Relatively unknown is the fact that cervical fractures or fracture-dislocations to restrained front seat occupants occur where no head contact was evidenced by both medical records and car inspection. A review of the available literature on car crash injuries revealed more than 100 such cases. A review of the National Accident Severity Study (NASS) 80-88 file was also conducted, revealing more examples. Case capsule descriptions from the authors' files are also detailed along with examples of such injuries in infants and children in child restraints. However, cervical fractures or fracture dislocations are rare, as evidenced by the relatively few cases identified in the literature, in the author's files, and by an analysis of NASS 80-90 data that revealed a cervical spine injury frequency of only .4% at the AIS-3 level (Huelke, Morris, and Mackay 1992).

Field investigations of the performance of air bag deployments in frontal collisions

This paper documents field investigations of "air bag" crashes selected from a large group of air bag crashes in file at the University of Michigan Transportation Research Institute (UMTRI). A full range of crashes are presented with injury levels of AIS 1-2 to AIS 5-6. Most occupants sustained minor injuries. Those not wearing the lap-shoulder belt (3-point belt) had more minor injuries than the restrained. The occurrence of higher level injuries (AIS > or = 2) was found more often in the nonbelted.

Air bag injuries and occupant protection

Analysis of the investigations of crashes involving automobiles equipped with air bags verifies the estimations of the lifesaving and injury reduction benefits of this supplemental restraint system. Cases of air bag-associated injuries, primarily erythema, abrasions, and contusions of the lower face and anterior throat-upper chest, are identified as those most often observed. Corneal-scleral injuries were infrequently noted but are rarely found in crashes involving air bag deployments.

Fatal injuries caused by underarm use of shoulder belts

Safety belt use has dramatically increased in the past decade in North America because of safety belt use laws. Underarm use of shoulder belts is a means of relieving neck irritation and other complaints from shoulder belts but may result in serious or fatal injuries. Loads far in excess of the injury tolerance of the lower chest and upper abdomen are imposed by the shoulder belt in the underarm position. Six recent cases are presented in which fatal injury was caused by underarm use of shoulder belts. Lacerations of the liver, spleen, intestines, mesentery, diaphragm, and aorta, and spine injury have occurred in accidents, most of which should have been survivable. The motoring public must be warned that underarm use of shoulder belts is hazardous and may cause fatal injuries in otherwise survivable accidents.

Seat belt effectiveness: case examples from real-world crash investigations

Although it may be well known that the lap-shoulder belts are effective in reducing occupant injury in motor vehicle crashes, hardly ever have actual examples been presented in the medical literature. This paper presents case histories of selected severe crashes in which one or more of the occupants were lap-shoulder belted. Environmental and vehicular details, as well as injury descriptions, are presented along with comments.

Use of quadruped models in thoraco-abdominal biomechanics research

Pigs and dogs have become common models of human thoraco-abdominal impact response. This paper summarizes a comparative analysis of the dog and pig to the live human accomplished through a series of necropsies performed on pigs and dogs. The results are summarized below. Emphasis is placed on specific aspects which are felt to be important for impact biomechanics. In particular, emphasis is placed upon the effect of tethering structures because of their potential in explaining mechanisms of injury for specific types of trauma such as aortic and certain liver injuries. Some aspects of tethering in the pig and dog are significantly different from that of the live human so care should be taken when using these animals in thoraco-abdominal biomechanics experiments.

Cervical spine biomechanics: a review of the literature

This article reviews the many clinical and laboratory investigative research reports on the frequency, causes, and biomechanics of human cervical spine impact injuries and tolerances. Neck injury mechanisms have been hypothesized from clinically observed cervical spine injuries without laboratory verification. However, many of the laboratory experiments used static loading techniques of cervical spine segments. Only recently have dynamic impact studies been conducted. Results indicate that crown-of-head impacts can routinely produce compression of the neck with extension or flexion motion. However, the two-dimensional (midsagittal) movement of the head bowing into the chest does not routinely produce flexion/compression type damage to the cervical spine. Flexion/compression damage to the cervical spine can be produced by prepositioning the subject so that upon impact, a three-dimensional motion of the head and neck occurs. Future laboratory research is needed to determine the forces and impact directions required to produce the various known fracture types and dislocations for a clear, accurate description of the cervical spine impact dynamics.

Facial injuries in automobile crashes

In automobile accidents, the facial area is the most frequently injured body region in passenger car occupants. Laboratory studies have indicated that the tolerance of facial bones to impact is relatively low. Most of these facial injuries are rated as minor. The windshield, steering wheel, and instrument panel are the major points of contact. Restraints, lap belts, and lap-shoulder belts reduce the frequency of facial injuries at all levels of severity and also reduce the more severe and serious injuries to other body regions.

Ocular injuries in automobile crashes

Tempered windshields commonly used in Europe have been shown to be related to the relatively high incidence of ocular injuries. Although windshields of the High Penetration Resistant (HPR) type in cars in North America are not at all significantly involved in ocular injuries, still about 50 % of the injuries of the eye area are caused by glass. The HPR windshield probably is the main reason for the relatively low occurrence of ocular injuries in United States crashes compared to these injuries reported from countries with tempered windshields. No ocular injuries were observed among belted occupants in this study. It appears that the increased use of lap-shoulder belts would decrease the likelihood of occupant contact with the windshield, mirrors, roof support, steering wheel, and instrument panel- about two thirds of the occupant contacts related to ocular injury- and thus reduce the incidence of ocular injuries leading to decreased vision.

Cervical injuries suffered in automobile crashes

The National Crash Severity Study data in which occupants sustained severe, critical-to-life, or fatal cervical injuries were reviewed. Of passenger cars damaged severely enough to be towed from the scene, it is estimated that one in 300 occupants sustained a neck injury of a severe nature. The neck-injury rate rose to one in 14 occupants for those ejected from their cars, although many of these injuries resulted from contacts within the car before or during the process of ejection. Severe neck injuries were rather rare in cars struck in the rear, but were more common in frontal and side impacts. Occupants between 16 and 25 years of age had such injuries more than twice as often as those in any other age group. Most of the neck injuries of a more severe nature involved the cervical spine or spinal cord. Injuries of the anterior aspect of the neck were relatively infrequent, and usually resulted from direct blunt impacts. National projections of the number of fatalities related to cervical injuries indicates that 5940 deaths, or approximately 20% of all in-car deaths, include fatal cervical spine injuries, and that about 500 cases of quadriplegia per year result from automobile accidents.

Cervical fractures and fracture-dislocations sustained without head impact

Because of its flexibility and structure, the cervical spine is disposed to various mechanisms of injury: although not so common as injuries caused by head impacts, cervical fractures and/or fracture-dislocations have been reported without direct impact to the head. Some cervical injuries reported have been sustained by wearers of lap and shoulder belts in auto accidents; however, we do not consider belt use a potential hazard because ample evidence has accrued in the medical and engineering literature to document general injury and fatality reduction by use of seatbelts. We believe that in many instances occupants would be more seriously injured or killed were belts not worn. The present paper reviews reports of cervical injuries without head impact found in the literature and case histories of such injuries from the Highway Safety Research Institute of The University of Michigan, as well as experimental studies in animals, cadavers, and volunteer subjects.

The hazard of the unrestrained occupant

A review of 208 cases involving injuries sustained by vehicle occupants was extracted from the computer storage at the Highway Safety Research Institute, University of Michigan, Ann Arbor. In addition, 157 new car crashes investigated by the authors were separately analyzed. Data analysis indicates injuries are sustained by direct occupant-to-occupant contact and by one occupant forcing another into or against one or more interior car structures. All body areas can be involved in this previously unreported injury mechanism, with the upper portion of the body more susceptibel to injury. Case histories from field accident investigations document a variety of these injury mechanisms.

Vertebral column injuries and seat belts

It is obvious from the above that there are several independent mechanisms in the production of the various types of lumbar fractures. The details of these mechanisms must be fully understood in each case of lumbar vertebral injury. The cases reviewed in the present paper show that similar if not identical lumbar injuries can occur in car occupants wearing or not wearing lap belts at the time of the crash. Thus, cauxally relating a lumbar injury to the lap seat belt is in error. Only distraction injuries located between 1-2 and 1-4 with no evidence of either compression or anterior wedging can be causally related to a lap belt. Even some injuries with this typical confuguration have been observed in persons who were not belted (10). Thus, without knowledge of details of the crunch, lumbar fractures could mistakenly related to use of the lap belt. Thoraculumbar injuries have been senn in patients who were ejected from the car some time during the crash event. Relating the ejection event to the lumbar fracture must be done with great caution. As has been shown by Roaf (48) and by Kaufer and Hayes (33), the type and location of the lumbar spine injury can frequently and indicatory of load application. Other body injuries, or lack thereof, are often good clues to determine the point of load application causing lumbar injury. In addition, it has been recomended that additional details of the injury and of the accident be obtained for accuracy reporting of seat belt injuries.

Automobile accident studies of maxillofacial injuries

The use of the available lap and shoulder belts would between 10,000 and 15,000 fatalities annually, and would significantly reduce the number of injuries, particularly those of the face. By mandatory seat belt usage laws a significant reduction in deaths, disfiguring injuries, and hospital bed-days would be realized.

Mechanisms of injury in automobile crashes

The only way to determine the causes of injury in automobile collisions is through examination of data collected in detailed investigation of crashes. Such data were gathered from a ten-year study of collisions that caused injury to the occupants of the cars. In a comparison of injuries in the newer model automobiles-vehicles equipped with the safety features-with those in older model cars not equipped with the present-day occupant protection devices, significant reduction in injury severity was noted.

Revascularization of the periodontium after tooth grafting in monkeys

In replanted and homo transplanted teeth a vascular network developed in the blood clot between the two parts of the torn periodontium, which allowed the grafted ligament to regain its vascularity. When dentoalveolar ankylosis developed, the periodontal vasculature was split into a number of vascular clusters. In homotransplants, a definite cellular immunologic response by the host was absent. An acrylic radicular obturator was used.