Understanding Trauma: Physics, Biomechanics, and Injury Mechanisms

Furthermore, Newton’s Second Law of Motion defines the relationship between force, mass, and acceleration:

$\text{Force} = \text{Mass} \times \text{Acceleration}$

In a trauma event, acceleration (speeding up) and deceleration (slowing down) are critical. High-speed motor vehicle crashes (MVCs) can generate massive deceleration forces measured in $g$ forces (multiples of gravity). While the human limit for deceleration is approximately 30 $g$, trauma patients often experience much higher forces.

Mechanism of Injury (MOI) and Index of Suspicion

The Mechanism of Injury (MOI) refers to the process by which energy is transferred to the body. By analyzing the MOI—such as the amount of vehicle damage, the presence of skid marks, or the position of the patient—paramedics can develop a high index of suspicion. This means anticipating specific injuries that may not be immediately visible during a physical exam.

Words of Wisdom: Suspect a spinal injury when you see a cracked windshield, bent steering wheel, dashboard damage, or intrusion into a vehicle.

Types of Trauma

Trauma is generally categorized into two types based on how the energy interacts with the skin:

1. Blunt Trauma: Occurs when energy is spread over a larger surface area without breaking the skin. This is often difficult to diagnose because it leaves few external signs.

2. Penetrating Trauma: Occurs when an object pierces the skin and damages underlying tissues.

Blast Injuries

Explosions create unique injury patterns categorized into five types: primary (pressure wave), secondary (flying debris), tertiary (body being thrown), quaternary (miscellaneous/burns), and quinary (chemical/radiant). Organs containing gas, such as the lungs and gastrointestinal tract, are most susceptible to these pressure changes.

Impact Patterns and Multisystem Trauma

Multisystem trauma involves injuries to several body systems (e.g., head, chest, and abdomen simultaneously). These patients are at high risk for mortality because the body cannot compensate for multiple major injuries as easily as an isolated one.

Motor Vehicle Crashes (MVCs)

In an MVC, the transfer of energy occurs in five phases: deceleration of the vehicle, deceleration of the occupant, deceleration of internal organs, secondary collisions (hitting objects inside the car), and additional impacts.

The type of impact determines the impact patterns:

• Frontal/Head-on: Often involves "up-and-over" or "down-and-under" trajectories.

• Lateral/Side Impact: Can cause severe crushing of the door and ribs.

• Rear-End Impact: Often results in whiplash or cervical spine injuries.

Internal Deceleration and Organ Injury

Even if the skin is intact, the internal organs continue to move during rapid deceleration. This can lead to shearing or rupturing of organs at their points of attachment.

The impact resistance of an organ depends on its contents. Gas-filled organs (lungs, intestines) scatter energy differently than solid (liver, spleen) or liquid (vascular system) organs.

The Trauma Lethal Triad

In the management of severe bleeding and multisystem trauma, paramedics must work aggressively to prevent the trauma lethal triad. This is a deadly cycle consisting of:

1. Hypothermia (low body temperature)
2. Coagulopathy (inability of blood to clot)
3. Acidosis (excessive acidity in the blood)

Failure to interrupt this cycle significantly increases the likelihood of patient death.