Biomechanics of Traumatic Brain Injury

Traumatic brain injury or a closed head injury can occur when the head is subjected to a direct external impact. Also, injury can occur when the head is subjected to a sudden acceleration and then is suddenly stopped. A sudden acceleration/deceleration often follows a violent flexion B 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: (a) impact of the brain against the skull; (b) shear between layers of the brain; and (c) cavitation.

(a) Brain v. Skull. Depending upon how the impact occurred, be it a rear end collision or other source, the head starts its movement to the rear while the brain resists, thereby leaving a space at the back of the skull. As this force progresses, a centrifugal force lifts the brain leaving spaces between it. Both inertia and centrifugal force causes the brain to hit 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. A blow to the head flings the brain against these bony proturbences and it is bruised and torn, resulting in brain damage

(b) Shear and Diffuse Axonal Shearing. Another type of brain injury is a 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. Often, 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 mild TBI or Traumatic Brain Injury, and is rarely visible upon imaging.

(c) Cavitation. 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. Often, 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.

An understanding of the biomechanics of injury are especially required in the proper trial presentation of any traumatic brain injury case. The Law Offices of Peter Miller work with world-class experts on this subject. Below, you will see the lengths to which the Law Offices of Peter Miller routinely works with biomechanical experts to demonstrate the mechanics of injury.

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