Traumatic brain injury or a closed head injury can occur when the head is subjected to a direct external impact (such as where the head is struck, or where the head strikes an object).

Likewise, injury can occur when the head is subjected to a sudden acceleration and then is suddenly stopped. A sudden acceleration/deceleration (oftentimes causing diffuse axonal shearing and other times causing coup/contra coup injuries) often follows a violent flexion-extension movement of the head. This response is extremely common in rear-end vehicle collisions.

Condensed to its most simplistic, there are three major mechanisms which contribute to traumatic brain injury. These include:

• impact of the brain against the skull;
• shear between layers of the brain; and
• cavitation.

Depending upon how the impact occurred, be it a rear-end collision or another cause, the head starts its movement to the rear while the brain resists, leaving a space at the back of the skull. As this force progresses, a centrifugal force lifts the brain, thereby leaving spaces between it. Both inertia and centrifugal force causes the brain to impact against the skull. This impact may cause damage to the brain.

While the skull provides considerable external protection because of its strength, its inner-contours are not smooth and are characterized by sharp, bony proturbences. When a blow is dealt to the head, the brain is flung against these bony proturbences and is bruised and torn, resulting in brain damage.

Another mechanism of brain injury is that of shear. Shear is based on rotational acceleration/deceleration, and a sliding effect of one layer of the brain upon another. Shear occurs within the brain because of the difference of density in layers.

Another mechanism of brain injury is that of shear. Shear is based on rotational acceleration/deceleration, and a sliding effect of one layer of the brain upon another. Shear occurs within the brain because of the difference of density in layers.

Axonal shearing can occur where an axon transverses between two or more layers of the brain which are subject to shearing forces. Oftentimes, damage to the axons is diffuse and degeneration happens throughout the brain rather than in specific clusters. Diffuse axonal shearing is a common cause of “miild” traumatic brain injury, and is rarely visible upon imaging.

Cavitation occurs when mass moves rapidly through fluid. The pressure in front of the mass is high and the pressure behind the mass is low. Vapor filled bubbles form in low pressure. When a mass returns in the opposite direction, the bubbles collapse. If this occurs often, the brain can be injured.

Many times, injuries are found opposite the point of impact. This type of injury is called the “countre-coup,” a French term meaning “against the blow.” Cavitation is the most commonly accepted explanation for this type of injury.

Work-up of the biomechanics of injury are especially required in the proper trial presentation of any traumatic brain injury case. The Scarlett Law Group works with the top experts in the world on this subject. Below, you will see the lengths to which the Scarlett Law Group routinely works with biomechanical experts in order to demonstrate the mechanics of injury.