Motor accidents

Presenter and Credentials

Vincent Tranchida, M.D.
 Medical Examiner
 Dane and Rock Counties, Wisconsin

OBJECTIVES IN THESE CASES

  • Determine the cause of death
     - Confirm that death was caused by injuries suffered in the accident, ensuring medical examination correlates with accident reports.
     - Assess the extent of injuries through a thorough autopsy, including evaluating trauma patterns.
     - Investigate any disease or factor (e.g., intoxication, pre-existing medical conditions) that might have precipitated or contributed to the death, and document these factors meticulously.

  • Detect any criminal activity associated with the death, including potential homicide or vehicular manslaughter.

  • Document findings for subsequent use in either criminal or civil actions, allowing for proper legal proceedings and ensuring evidence fidelity.

  • Establish positive identification of the body, especially if it is burnt or severely fragmented, utilizing DNA testing and dental records if necessary.

INJURIES

  • Injuries in motor vehicle crashes are the result of:
     - Impaction of the individual on some portion of the interior of the car, leading to soft tissue injuries, fractures, and potentially fatal trauma.
     - Violation of the integrity of the passenger compartment by intrusion of part of the car or of another object (e.g., another vehicle or lamppost) into the passenger compartment, causing serious injuries from penetrating trauma.
     - Ejection from the motor vehicle, either in part or entirely, substantially increasing the risk of death and severe injury.
     - Fire (rarely), but can lead to severe burns and respiratory injuries due to fire inhalation.

CAUSES OF MOTOR VEHICLE ACCIDENTS

  • The most common cause of a fatal motor vehicle accident in the U.S. is impairment of the driver by alcohol, drugs, or a combination of both.
     - Statistics:
     - ½ of all motor vehicle operators killed in crashes are under the influence of alcohol.
     - If considering only drivers who cause accidents, then 65-75% are to some degree under the influence of alcohol or drugs, including prescription medications, indicating a troubling trend of substance use while driving.

  • The second most common cause is human error, including:
     - Speed (usually associated with alcohol intoxication)—speeding increases both the severity of the accident and the likelihood of fatal outcomes.
     - Reckless driving, contributing to unsafe maneuvers, disregarding traffic laws.
     - Falling asleep at the wheel, particularly in long-haul drivers, emphasizes the need for safe driving practices and regular breaks.
     - Texting/checking email, a prevalent distraction with severe consequences.

  • The third most common cause is environmental hazards, such as:
     - Bad weather, which can result in poor visibility and slippery conditions.
     - Slick or icy roads, where loss of traction can lead to loss of vehicle control.
     - Poorly marked roads, causing ambiguity in navigation could lead to dangerous maneuvering.
     - Poorly constructed roads, which may have hazards or insufficient signage.

  • After these factors, miscellaneous causes (including defective vehicles, natural disease, etc.) are identified, requiring comprehensive vehicle inspections following incidents.

NATURAL DISEASE AS A CAUSE OF MVAS

  • Accidents caused by natural disease are rare, typically only resulting in the death of the driver, with the cause of death mainly being a result of natural illness compromising their ability to drive.
     - Drivers are often able to stop or significantly slow down the vehicle before a collision occurs.
     - When a collision does occur, it is usually at low speed, leading to minor injuries or collateral damage.

  • The primary cause of death usually is ischemic (atherosclerotic) heart disease (113 out of 134 cases in one study, or 76.9%), demonstrating the importance of evaluating a driver's medical history before assigning fault.
     - Other causes include:
     - Aortic aneurysm (6 cases).
     - Cerebrovascular infarcts (8 cases), often linked to prior undiagnosed conditions.
     - Fatalities include 6 from the rupture of a cerebrovascular aneurysm and 2 from hemorrhagic cerebrovascular infarcts, underlining the need for thorough medical investigation post-accident.

CATEGORIES OF MVA

  • Motor vehicle accidents can be divided into four categories:
     1. Front impact crashes—often the most deadly due to direct involvement with the windshield and dashboard.
     2. Side impact crashes—also known as T-bone accidents, often result in severe injury to the side of the vehicle.
     3. Rollovers—high risk of ejection and severe injury due to the dynamics of vehicle motion.
     4. Rear impact crashes—often less fatal but can lead to significant whiplash injuries.

  • The probability of a fatality depends to a degree on the size and type of vehicle involved in a crash, emphasizing the disparity in safety across vehicle categories.
     - Small vehicles, by virtue of their size, are less able to absorb crash energy, leading to more severe injuries and fatalities compared to larger vehicles.
     - Conversely, pickups and sports utility vehicles (SUVs) are generally heavier, which tends to improve occupant survival rates in crashes; however, they are nonetheless more likely to be involved in fatal single-vehicle crashes, particularly in off-road incidents.

FRONT IMPACT CRASHES

Mechanics of Front Impact Crashes

  • Involves two vehicles crashing head-on or a vehicle crashing into a fixed object, creating significant forces upon impact.

  • If the driver and passengers are unrestrained, occupants will continue moving forward even after the vehicle stops, leading to severe injuries upon impact with the vehicle interior.

Patterns of Injury

  • Unrestrained occupants:
     - Driver’s knees impact the instrument panel, often resulting in fractures or contusions.
     - Chest impacts the steering wheel, which can lead to rib fractures or internal bleeding.
     - Head impacts in decreasing order of incidence:
     1. Windshield—commonly leads to lacerations and concussions.
     2. Sun-visor region above the windshield—may cause facial fractures.
     3. Frame of the vehicle—can lead to intracranial hemorrhaging in severe cases.
     - Similar injuries occur for front seat passengers, who impact the dashboard with their chest rather than the steering wheel.

  • If the front impact is off-center, the driver or passenger might impact the A pillar with their head, resulting in potential cervical spine injuries.

  • Unrestrained individuals in the backseat will hit the back of the front seat, increasing the risk of whiplash or spinal injury.

  • If the driver is restrained by seat belts but without an airbag, the knees will impact the instrument panel, and the head typically flexes forward, with the chin potentially impacting the sternum or the steering wheel in severe collisions, causing additional trauma.

Additional Injury Considerations

  • Objects protruding from the instrument panel (such as levers or knobs) can produce patterned abrasions on victims, which may serve as evidence in investigations.

  • If restraints are used and the passenger compartment retains its integrity, occupants should survive without significant injury; however, injuries from intrusion are possible, necessitating detailed examinations.

  • If the driver or front passenger impacts the windshield, common results include abrasions and superficial cuts of the forehead, nose, and face, often with vertical orientation injuries, pointing to the rapid forces during collisions.
     - Thin slivers of windshield glass may embed in the wounds, complicating treatment and highlighting the need for forensic analysis.
     - Severe soft tissue injuries can occur due to head impacts, which may distract from more serious internal injuries that also require identification.

Internal Injury Types

  • Impacts can cause:
     - Basilar skull fractures, which are especially dangerous due to proximity to brain structures.
     - Closed head injuries with potential long-term effects on cognitive function.
     - Fractures of the neck, demanding immediate medical attention.
     - Common upper cervical fractures/dislocations leading to significant spinal cord injury, which can result in paralysis.

  • Typical torso injuries include:
     - Transverse fracture of the sternum (usually at the level of the 3rd intercostal space), which can complicate respiratory function.
     - Bilateral anterior rib fractures, often dangerous due to the risk of impaling injuries to vital organs.
     - Impaling injuries to the lungs due to fractured ribs, which can complicate patient outcomes significantly.
     - Lacerations of the lungs, rupture of the heart, transection of the aorta, and lacerations of the liver and spleen, emphasizing the severity of the trauma in front impact accidents.

  • Injury patterns can vary widely among young individuals due to the elastic nature of the sternum and ribs, possibly leading to severe internal injuries without visible fractures, thus requiring comprehensive assessment.

  • One common fatal thoracic injury is transection of the aorta, typically occurring distal to the left subclavian artery's origin, which necessitates immediate intervention for survival.
     - This injury is often associated with rapid deceleration and chest compression, underscoring the need for vehicle safety features.

  • Furthermore, injuries to the heart, while less frequent, can involve myocardial contusions and various ruptures across heart chambers (right atrium, ventricle, and left atrium), which can rapidly lead to death if not addressed promptly.

  • Occasionally, fatalities arise from “commotio cordis,” or fatal arrhythmias caused by cardiac contusions, particularly in accidents without visible anatomical causes of death that would inform the inspection process.

SEAT BELTS AND AIR BAGS

Restraint Systems

  • There are three forms of automobile belt-type restraints:
     1. Lap belts—offer limited protection and tend to cause abdominal injuries due to slippage.
     2. Shoulder (diagonal) belts—provide better restraint of the upper body.
     3. Three point belts (lap plus shoulder belts)—considered the standard for safety.

  • All new vehicles use three-point belts, while lap and shoulder belts may still be found in older vehicles, indicating the need for updating safety standards in older models.

  • Seat belt abrasions can provide crucial information regarding occupant positioning during high-energy collisions, aiding in the reconstruction of accident events.

Effectiveness

  • Seatbelts drastically reduce mortality and morbidity by minimizing occupant-to-interior impacts, proving crucial in collision survivability.

  • They nearly eliminate ejection incidents, even in rollover crashes.
     - One study indicated a reduction in fatality risk for front-seat occupants by 45%, illustrating their life-saving capacity.

  • Without seat belts, 75% of ejected occupants from passenger cars are killed, versus only 1% of restrained occupants, underscoring the importance of proactive safety measures.

Injury Risks

  • Despite benefits, seat belts and airbags can also cause injuries or fatalities, particularly among shorter individuals or children unrestrained during deployment, presenting a paradox in safety.
     - Characteristic abrasions may appear on the anterior neck, underside of the jaw, and chest due to airbag deployment, which requires careful documentation and examination.
     - Fatal injuries can include cervical spine dislocations, skull fractures, and thoracic organ injuries, necessitating thorough medical evaluations for those involved.

  • Individuals seated closer than 10 inches to the steering wheel face higher risks from deploying airbags—highlighting the critical need for manufacturers to consider different occupant sizes.

Child Safety Considerations

  • Rear-facing infant or child restraints should not be used in front seats due to proximity to air bag housing, risking severe injury primarily to the skull, emphasizing the need for proper placement of child safety systems.

MOTORCYCLE ACCIDENTS

General Statistics

  • Approximately 6% of all traffic fatalities involve motorcycles, underlining their risk factor compared to cars.

  • Motorcycles present a significantly higher risk of ejection compared to automobiles, leading to increased likelihood of severe injuries with minimal automobile incidents resulting in only minor injuries due to the lack of protective structure in motorcycle design.

Common Injuries

  • Fatalities often result from extensive head or neck injuries, predominantly skull fractures, emphasizing the importance of wearing helmets which significantly mitigate head trauma occurrences at lower speeds although their effectiveness reduces as speed increases.

  • Protective clothing is crucial as injuries can lead to superficial abrasions without subcutaneous hemorrhage, risking further complications in healing.

  • Common injuries upon falling off include lacerations of the head, fractures of the skull, and abrasions to various body parts, often requiring surgical intervention.

Causes

  • The overarching causes of fatal motorcycle accidents include:
     - Alcohol or drugs (most predominant cause)—approximately 28% of motorcycle operators involved in fatal crashes have a blood alcohol concentration of 0.10 g/dl or greater, emphasizing a critical public safety concern.
     - Environmental hazards including slick or poor road conditions, which repeatedly contribute to accidents and demand better safety measures in road maintenance.
     - Reckless driving and driver inattention, particularly from those in cars not seeing motorcycles, illustrating the need for driver awareness campaigns to improve road safety.

PEDESTRIAN IMPACTS

Factors Influencing Injury Patterns

  • Injury patterns and severities when a pedestrian is struck by a vehicle depend on:
     - The speed of the vehicle—high speeds generally result in severe or fatal injuries.
     - The physical characteristics of the vehicle—larger vehicles can lead to more severe impacts.
     - Whether the vehicle was braking—vehicles moving at higher speeds without braking increase the risk of severe injury.
     - The age of the victim (child or adult)—children are often at greater risk due to their smaller size and unpredictability.

Vehicle Speed Analysis

  • The speed of the vehicle is a critical determinant in the causation of severe injuries:
     - Injury speeds:
     - Fracture of the spine appears at 17 mph and is almost always present by 42 mph, emphasizing the critical thresholds for potentially fatal impacts.
     - Rupture of the thoracic aorta manifests from 39 mph and is always present by 53 mph, showing the correlation between speed and the severity of internal injuries.
     - Inguinal skin ruptures at 41 mph, with consistent results at 59 mph, signaling the increase in damage relative to impact force.
     - Dismemberment appears at 34 mph, highlighting the devastating potential of high-speed collisions.

Impact Dynamics

  • Children struck typically have impact occurring above their center of gravity, leading to crushing injuries and possible tire imprints, while adult impacts generally happen below the center of gravity, leading to varying injury sequences (wrap, fender vault, etc.).
     - Hidden injuries, such as internal hemorrhage, can sometimes go undetected until dissection, necessitating in-depth medical examinations post-accident.

THANK YOU

  • Mary Ward (1827-1869), known as the world's first recorded motor vehicle accident fatality, was a scientist in Ireland who fell under the wheels of an experimental steam car built by her cousins, an example illustrating the early recognition of the dangers associated with motor vehicles.