Mechanism of Injury

Flexion/Extension Force

One of the most widely recognized causes of concussion is a motor vehicle accident (MVA). Severe flexion/extension (whiplash) occurs, in which the brain is propelled forward and backward, striking the front and back of the skull. This is called a coupe contra/coupe injury, see the image below. During a MVA, the vehicle stops suddenly, and the body continues to move forward until restrained by the safety belt. The head continues forward until restrained by the neck. The brain continues to move forward until it hits the skull. If the head is positioned forward, the brain hits the sinus cavities creating microscopic tears in the front sections of the brain (prefrontal cortex). This region of the brain controls executive functioning, such as decision making, mental control, and self-regulation. The brain then bounces backwards striking the back, inside of the skull (occipital cortex). This region of the brain regulates vision and visual processing. The nature of this impact will create diffuse bruising as the skull is smooth and curved at the back.

Rotational Flexion/Extension Force

Rotational flexion/extension injury is when the head is not only subjected to flexion/extension forces, but rotational forces to the left, right or both. Thus, the brain not only hits the front and back of the skull, but can impact the sides as well. The sides of the brain (temporal lobes, frontal cortex, and parietal cortex) can be injured in addition to the front and back. These areas of the brain are responsible for auditory perception, important cognitive control, and sensory/perception respectively. Rotational flexion/extension forces commonly occur from impacts on the side of the head, as seen primarily in contact sports or direct blows (e.g., by a fist).

Vibration / Slip and Fall

Severe vibration is rare in the general population, but seen in certain athletes (i.e. luge or skeleton racers) and various occupations. It is believed that the constant vibration of the head being forced up and down produces microscopic tears in the brain which accumulate over time.

Forces to the tailbone from a slip and fall are transmitted up the spine, and impact the brain by driving it into the top of the skull. This type of accident does not often result in immediate MTBI symptoms, but symptoms of dementia and Parkinson-like tremors may manifest a few years later.


If headaches are reported as a post-concussive symptom, whiplash must be considered as a contributory cause. MTBI, by its definition, implies a sudden stop or change in direction involving the head and consequently the neck. A sudden stop/change in direction causes strains or sprains of the muscle, and disturbances in how the muscles work together. Unless treated, these muscles develop what are known as “trigger points” that cause pain. Several muscles in the neck refer pain directly into the head. It is also important to consider the status of the cervical neck vertebrae if the headaches continue.

Comorbid Factors

In medicine, the term "comorbid" refers to medical condition(s) existing simultaneously, but independently, with another condition; or a related medical condition or conditions in addition to a primary condition. Effects are evident in both physical and psychological health. Due to the nature of brain injuries, changes occur in the complex, internal functions of the body, such as the systems responsible for regulating body temperature, blood pressure, and bowel and bladder control.

Post concussion syndrome contains many features seen in psychological conditions. For example, the reported symptoms of ADD are very similar to that of MTBI. Other psychological factors such as depression, anxiety, and social issues may also worsen due to MTBI. The reasons or mechanisms involved in this phenomena are not presently understood, and family relationships often become strained and dysfunctional. Research indicates that without intervention, 90% of persons injured in a motor vehicle accident are divorced within 5 years. Research also indicates that 45% of the homeless have suffered concussions. Before the MTBI occurred, 87% of those homeless individuals owned their own homes.