Flexion / Extension Forces
Motor vehicle accidents (MVA) are a common cause of concussion that often result in severe flexion/extension. This can occur in other instances, such as a full or in sports.
With this type of injury, the brain is propelled forward and backward, striking the front and back of the skull. This is called a coupe-contra/coupe injury. During a MVA, for example, the vehicle stops suddenly, and the body continues to move forward until restrained by the seatbelt. 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 skull on the other side of the sinus cavities behind the nose and eyes. This creates microscopic tears in the front sections of the brain (prefrontal cortex), which controls executive functioning (e.g. decision making, mental control, and self-regulation). The brain then bounces backwards striking the back of the skull where your visual processing area is located (occipital cortex). The nature of this impact will create diffuse bruising as the skull is smooth and curved at the back.
Rotational Flexion / Extension Forces
Rotational flexion/extension injury is when the head is not only subjected to flexion/extension forces, but also 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) are responsible for auditory perception, important cognitive control, sensory/perception respectively, and much more. 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 / Tailbone
Severe vibration is rare in the general population, but it is seen in certain athletes (e.g. 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.
One lesser known cause of concussion is a tailbone impact. The forces caused by landing on the tailbone can travel up the spine and drive the brain into the top of the skull. This type of accident does not always result in immediate concussion symptoms, but long-term consequences found in post-concussion syndrome can occur.
If headaches are reported as a post-concussive symptom, whiplash must be considered as a contributory cause. Mild traumatic brain injuries, by definition, imply a sudden stop or change in direction involving the head and consequently the neck. This causes strains or sprains of the neck and back muscles, and disrupts 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, so if headaches are a persistent symptom, the source could be in the neck. It is also important to consider the status of the cervical neck vertebrae if the headaches continue. If the forces were great enough, there could be a spinal injury that requires immediate medical attention.