Concussions are thought to involve two different injuries- a primary mechanical injury and a secondary metabolic injury.
Two Modes of Injury
The primary injury is the event which caused the mechanical damage to the brain cells as a result of shearing, tearing, and/or stretching.
The secondary injury evolves–minutes to hours, hours to days, and possibly even days to months after the initial traumatic event. The secondary injury is the result of a delayed biochemical, metabolic, and cellular changes that are initiated by the primary injury.
Diving Deeper
Primary: The primary injury occurs as a result of combined linear and rotational accelerations to the brain. Many different head motions can occur from a concussion. This complex variety of responses makes each concussion unique. Brain tissue deforms more easily in response to shear forces compared to other biological tissue. Rapid head rotations generate shear forces throughout the brain causing tissue damage. Therefore, injuries producing rapid head rotations, even without a direct impact to the head, can cause a brain injury. In fact, if the head motion is constrained to exclude any rotational motion, it is difficult to produce traumatic unconsciousness.
Secondary: The secondary injury results as a consequence of the external forces impact on the brain. This impact creates stretching and disrupting of brain cells. This sets off a cascade of metabolic changes which results in the brain having less blood than normal, less fuel than normal, less energy than normal, and is working harder than normal to try to restore balance. Over time if this process does not correct itself it will lead to the death of brain cells as you see in chronic traumatic encephalopathy (CTE). This process of the secondary injury is thought to account for many of the neurological deficits observed after TBI. As a consequence, many treatments for post-concussion focus on targeting this metabolic cascade.
Helps to Explain the Unexplained…
When assessing for a concussion, both modes of injury must be addressed. The modes may explain why symptoms are not always associated with a concussion. When months pass between the injury and the onset of symptoms, it is hard to make the connection. This explains why unexplained symptoms begin to surface unexpectedly..
If you are curious about symptoms surfacing for no explained reason, contact us to schedule a consult. We can answer any questions you may have regarding concussion and traumatic brain injury.
