The event of being run over by a car represents one of the most severe forms of high-energy blunt force trauma the human body can sustain. This type of pedestrian-vehicle accident (PVA) is distinct from a simple impact, involving a crushing mechanism that generates massive compressive and shearing forces. The result is a complex, multi-system injury pattern that immediately threatens life.
The Kinematics of Vehicular Trauma
A typical pedestrian-vehicle collision follows a sequence of three distinct physical phases, only the last of which constitutes the “run over” scenario. The initial event is the primary impact, where the vehicle’s bumper or leading edge strikes the pedestrian, usually impacting the lower extremities like the knees and shins. This sudden force causes the body to accelerate rapidly toward the speed of the vehicle.
The second phase is projection or vaulting, which occurs as the pedestrian’s body rotates over the car’s hood and, often, strikes the windshield or A-pillars with the head and upper torso. The body then separates from the vehicle and begins its trajectory toward the ground. This initial sequence determines the secondary injuries sustained from the impact itself.
The critical phase for a “run-over” event is the final one, where the vehicle’s tire passes directly over the body, or the body is crushed against the rigid road surface. This moment applies a concentrated, enormous load, resulting in massive compressive and shearing forces. The weight of the vehicle acts as a press, squeezing the body’s tissues and organs between the tire tread and the unforgiving ground.
Categorical Injury Patterns
The crushing force of a vehicle wheel creates specific and devastating injury patterns across multiple body systems. One of the most common and dangerous consequences is severe skeletal and pelvic trauma. Unstable pelvic fractures are a hallmark of this crushing mechanism, as the pressure can shatter the bony ring into multiple fragments.
Long bones, such as the femur and tibia, frequently sustain complex, open fractures where the bone breaks into many pieces and pierces the skin. This degree of skeletal injury is compounded by soft tissue damage, including muscle lacerations and traumatic avulsions. A specific type of soft tissue injury, known as a degloving injury, results from the shearing force separating large layers of skin and underlying tissue from the fascia and muscle.
Internal organ damage in the torso is a direct result of the crushing force squeezing the organs against the vertebral column. Solid organs like the liver and spleen are prone to laceration and shattering, leading to rapid, life-threatening internal bleeding. Hollow organs, such as the bowel and bladder, can also be perforated or ruptured by this extreme compression.
Head and spinal injuries resulting from a run-over are often dependent on the exact point the wheel crosses the body. While a secondary impact with the hood or ground can cause traumatic brain injury, a direct crush of the head or neck results in catastrophic, unsurvivable damage to the cranium or cervical spine. Injuries to the trunk frequently involve serial rib fractures, which compromise the stability of the chest wall.
Variables Determining Outcome Severity
The final outcome of a run-over incident depends on several variables that modulate the applied force. Vehicle characteristics play a major role, as the mass and height of the vehicle directly influence the magnitude of the crushing force. Being run over by a heavy sports utility vehicle (SUV) or a truck, which distributes a greater load over a smaller tire contact area, results in more severe injuries than a collision with a lighter sedan.
The speed of the vehicle at the point of impact is another significant factor, as kinetic energy increases exponentially with velocity. Even a small increase in speed can dramatically raise the risk of fatality, with the probability of death rising steeply at speeds above 40 kilometers per hour. A faster speed also increases the distance the pedestrian is dragged or thrown, leading to greater shearing and secondary impact injuries.
Pedestrian factors, including age and overall health, also influence the specific pattern and severity of trauma. Children, due to their lower height, often sustain an initial impact higher up on the body, leading to a greater frequency of head injuries. Older adults may suffer more severe fractures, such as serial rib fractures, due to reduced bone density and overall physiological fragility.
Immediate Systemic Complications
Beyond the localized anatomical damage, the severe trauma of a run-over immediately triggers systemic complications. The most immediate cause of death is often hemorrhagic shock, resulting from the rapid loss of blood from damaged internal organs and major blood vessels. Unstable pelvic fractures, in particular, can cause extensive bleeding into the pelvis that is not immediately visible externally, leading to rapid circulatory failure.
Another consequence of severe crushing is Crush Syndrome, a condition resulting from traumatic rhabdomyolysis. The pressure causes skeletal muscle cells to die and rupture, releasing toxic intracellular contents, including myoglobin, potassium, and lactic acid, into the bloodstream once the pressure is relieved. The release of myoglobin, the protein responsible for oxygen storage in muscle, can overwhelm the kidneys, leading to acute kidney injury (AKI).
The sudden surge of potassium, known as hyperkalemia, is dangerous because it can disrupt the electrical stability of the heart, causing fatal cardiac arrhythmias. The combined effect of flail chest from multiple rib fractures and internal bleeding compressing the lungs can lead to significant respiratory compromise. This instability of the chest wall prevents effective ventilation, making it difficult for the body to maintain adequate oxygen levels.