What is Rotational Brain Injury?

When the head strikes a ball, another head, elbow, knee or the ground, the impact is almost never straight on, but angled. This angled impact causes a sudden acceleration and deceleration of the head, and the brain to rotate inside the skull.

What Happens Underneath?

An impact to the head will involve both linear forces and rotational forces.

Linear forces are direct straight-line forces that compress or stretch the brain within the skull. Rotational forces are angled forces to the head from a ball, head, elbow, knee and ground. Rotational forces twist and shear the brain and brain cells.

Nature did not design the brain for rotational forces and injury, with the brain being badly designed for sudden rotational acceleration and deceleration. In sport the brain is subjected to sudden acceleration and deceleration, because it is rotated from impacts at the side and back of the head e.g., a head to head, head to ball, head to ground contacts and hits.

The white and grey matter of the brain is made up of differing densities, which means the jelly-like brain sections move at different speeds when rotated, this causes twisting of the brain, shearing of brain cells, brain cell death and the disruption of the nerve cell connectivity networks in the brain.

Head impact diagram

Brain injuries can be invisible

It’s not the force of the impact itself to the head in sport, but how the force causes the brain to move inside the skull that is significant to cause damage.

Rotational brain injury happens at the microscopic level – 4,000 times smaller than the eye can see on a regular brain scan.

Rotational brain injury bares few physical symptoms, which makes the invisible brain damage difficult to detect.

Brain scan

What Damage Does Rotational Brain Injury Cause?

Brain nerve cells (neurons) send and receive signals from the brain. The axon of the neurons carries information and allows for the transmission of electrical and chemical signals to other brain cells. Axons have a long-tail like structure, and are insulated with a fatty substance called myelin. Myelin helps axons conduct the electrical signal. The cell body contains genetic information, and maintains the neurons structure and provide energy. With rotational forces, axons become twisted and shear as shown in the diagram, resulting in neuronal (brain cell) death.

Rotational brain cell damage diagram

The brain operates via a highly complex network system, with information being organised and exchanged from one brain cell to another brain cell via nodes (as shown in the diagram below). These are junctions/roundabouts where information is diverted, nodes are placed all over the brain. Damage to these nodes (as shown in the diagram with Node 13 being damaged, this now means that other nodes try to take up the “traffic”). Damages to nodes causes complications and decreases processing power that reduces information flow, meaning reduced thinking ability (memory, thought processing, judgement, reactions, and changes in personality). Some of the most important nodes are located where the brain is most likely to be damaged by rotational injury encountered from contact sports.

Brain nodes diagram

What are the Risks of Rotational Brain Injury?

Rotational brain injury causes concussion, increases the risk of diffuse axonal injury (DAI), which is additional disruption of the nerve cells and tracts, and to long-term neurodegenerative diseases including Chronic Traumatic Encephalopathy (CTE).

Who is at Risk?

Everyone playing contact sport, because of the higher risk of having impacts to the head and causing the brain to suddenly rotate inside the skull.

The brain reaches 90% of its adult size by age 6. Between ages 8-12 is when peak development of the brain occurs (Brain development during childhood and adolescence: a longitudinal MRI study, 1999), but the brain is still developing important connections between cells until early 20s, a process known as myelination. With reduced myelin, the protective coating around nerve cells, children and youths are more susceptible rotational brain injury. The younger you are exposed to rotational brain injury and more injury you take, the greater risk of long-term neurodegenerative diseases.

In women, brain cells are longer and thinner, meaning they shear more easily. This is one of the reasons why females are at least three times more seriously impacted by concussion than males, with longer recovery time, longer and more pronounced post concussive symptoms.

Rotational brain injury is not specific to elite or professional sport, it is very much part of amateur sport. It impacts men, women, children, whatever age and fitness level.

Women's rugby tackle

Summary

In summary, impacts to the head create rotational forces which cause your brain to rotate inside the skull and brain cells to shear. Rotational brain injury causes concussion, increases your risk of diffuse axonal injury (DAI) and long-term neurodegenerative diseases including Chronic Traumatic Encephalopathy (CTE).

When you multiply every training session, every game and match over every year of playing, whatever your level or your game – that’s the potential for thousands of accumulated impacts to the head, and greater likelihood of rotational brain injury.