The personal bias of the author should be clearly understood so that the opinions given in this presentation may be kept in proper context. The author is a practicing orthopaedic surgeon, medical school faculty member and principal investigator of a U.S. DOT Multidisciplinary Accident Investigation team. Reduction or prevention of long-term disability which frequently follows severe musculoskeletal injuries is the overriding goal of the author.
The nature of accidents causing life threatening and/or disabling injuries appears to have shifted since enactment of the 1966 National Highway and Traffic Safety Laws because of improved vehicle design. In the past, head-on impacts were the most common source of serious injury but in recent years, side impacts, pedestrian and motorcycle accidents appear to be the principal causes of serious injury accidents. Additionally, whiplash remains a problem in spite of its minor nature and the introduction of head restraints. Belt type restraint systems appear to be causing some injury which may be reduced by improved design of the restraint system or vehicle seat. Particular attention is given to restraint systems because the motoring public is unjustly critical of even minor failures in safety equipment function and does not understand safety equipment injury trade-offs.
The head and chest remain the most common causes of fatal injury. Trauma indicating simulations for these areas have been under development for many years and will not be considered in this presentation. The neck is possibly the most commonly injured structure because of the high frequency of rear-end impact accidents resulting in hyperextension (whiplash) injury. Recent studies by the Insurance Institute for Highway Safety and by the author’s MDAI team indicate that head restraints reduce neck injury approximately 15%. This disappointing figure is apparently caused by two factors; failure of users to properly adjust head restraints and inadequate design of head restraints. Fixed head restraints appear to be a desirable ultimate goal so that active participation of the occupant is not necessary.
Differential rebound appears to occur because of differences in the spring rates of the head rest and seat back construction. Improved knowledge of human neck and dorsal spine kinematics and attention to seat design may resolve this problem. Present anthropomorphic dummy designs are primitive. A body of human volunteer experiments exists which, with further study, may reveal some of the details of neck kinematics which need to be incorporated in the dummy neck design.
Belt restraint systems particularly in the abdominal area appear to be failing occasionally because of submarining although the frequency of serious injury remains remarkably low. More accurate simulations of the human abdomen, pelvis and hips in conjunction with more extensive dummy testing in vehicles with suspension systems and production seats may elucidate the causes of failure of the belt system to better protect the occupants. The lap belt appears to slip off the bony pelvis and sweep upwards across the abdomen rupturing vital organs or forcing them into the chest cavity.
Serious lower extremity injuries continue to occur with alarming frequency and cause serious permanent disability which occasionally prevents a patient from returning to gainful occupation. Motorcycle and pedestrian accidents now appear to be the most common cause of injuries; because most automobiles are now equipped with occupant protecting dashboards, windshields, steering wheels and steering columns. Direct impacts against the lower extremities are the typical injury mechanism in pedestrian and motorcycle accidents. In-vehicle injury mechanisms include direct impact on the knee in the axis of the femoral shaft causing injury to either the patella, knee, femur or hip. Direct impact injuries of the lower leg may also occur inside the vehicle. Forced dorsiflexion of the foot and ankle against the knee fixed in the dashboard early in the accident sequence in head-on impact accidents may result in serious foot and ankle injuries if the engine elevates the toepan under the foot.
Disability in these situations occurs primarily from joint injury; bones virtually always heal although healing time may take several years. Traumatic arthritis is the result of joint injury and is a poorly defined little recognized entity. Initially, joint cartilage may not appear damaged and injury becomes clinically evident only a year or more after injury. Disability resulting from traumatic arthritis is caused by painful, stiff joints requiring the permanent use of crutches or canes. More sophisticated simulations of the lower extremities are necessary to measure energy input into joints. Range of motion and pressure measurement must be built into dummies to permit accurate injury detection.
KeywordsWhiplash Injury Neck Injury Lower Extremity Injury Motorcycle Accident Restraint System
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