Donald F. Huelke

Infants and children in the adult world of automobile safety design: Pediatric and anatomical considerations for design of child restraints☆

U.S.A. Abstract-The infant and child differ structurally from the adult in a number of ways which are critical to the design for protection against impact forces and for adequate occupant restraint systems. The purpose of this paper is to bring together a profile of the anatomy, anthropomctry, growth, and development of the infant and child. Age differences related to the proper design of child restraint systems are emphasized. Problems discussed include child-adult structural differences, center of gravity of the body, the head mass in relation to the neck and general body proportions, positions of key organs, and biomechanical properties of tissues.

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.

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.

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.

Cervical Spine Injury Mechanisms

A test series using eight unembalmed cadavers was conducted to investigate factors affecting the creation of cervical spine damage from impact to the crown of the head. The crown impact was accomplished by a free-fall drop of the test subject onto a load plate. The load plate striking surface was covered with padding to vary the contact force time characteristics. The orientations of the head, cervical spine, and torso were adjusted relative to a laboratory coordinate system to investigate the effects of head and spinal configuration on the damage patterns. Load and acceleration data are presented as a function of time and as a function of frequency in the form of mechanical impedance. For the covering abstract of the conference see HS-036 716. (Author/TRRL)

Removal of the Temporalis Muscle from Its Origin: Effects on the Size and Shape of the Coronoid Process

Removal of certain masticatory muscles from their mandibular attachment has produced a decrease in the size of the regions of insertion, particularly of the coronoid process and mandibular angle.1-5 In these studies, the temporalis, medial pterygoid, and masseter muscles were removed from their mandibular attachment or were almost totally extirpated. It has been concluded that the maintenance of the form of the bony processes to which these muscles attach is the result of muscle tension. Also, it has been shown that the arteries supplying the coronoid process, angle, and condyle of the rat, guinea pig, monkey, and man arise from vessels that supply the muscles attaching to these processes, and generally not from the inferior alveolar artery which primarily supplies the mandibular body and teeth.6-9 Therefore, it would seem that removal of the masticatory muscles from their mandibular attachment would eliminate the arterial supply to these bony processes. If, however, the blood supply of the mandible is maintained while direct muscle tension is decreased or eliminated by separating the masticatory muscles from their cranial attachment, the effect of the lack of muscle tension could be evaluated. It is the purpose of this study to note the effects on the coronoid process produced by removal of the temporalis muscle from its cranial origin.

RESPONSE OF THE CERVICAL SPINE TO SUPERIOR-INFERIOR HEAD IMPACT

A test series using 12 unembalmed cadavers was conducted to investigate factors affecting the creation of cervical spine damage due to impact to the top of the head. The test subjects were instrumented to measure head, T8 thoracic spine, and sternum acceleration responses. Photographic targets on the head and torso allowed analysis of impact motions from high-speed movies. The stationary test subject was struck by a guided, moving impactor mass of 56 Kg at 4.6-5.6 m/s. The impactor striking surface consisted of a biaxial load cell with padding to vary the contact force-time characteristics of the head/impactor. The orientation of the head, cervical spine, and torso was adjusted relative to the impactor axis to investigate the effect of spinal configurations on the damage patterns. Load and acceleration data are presented as functions of time and as functions of frequency in the form of mechanical impedance. Damage to the cervical spine was produced in all but one test, including fractures of the spinous processes, laminae, transverse processes, and the bodies of the vertebrae as well as ruptured discs and torn ligaments. Both anterior and posterior damage was produced and the sites of the damage ranged from C2 to T4. The peak forces produced during the impacts ranged from 1.8 kN to 11.1 kN. The limited response data of this pilot study do not allow any specific conclusions with regard to cervical spine tolerance levels. However, it does attest to the influence of spinal configuration and impact conditions on both response and damage of the spine due to crown impact.

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.

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.

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.