Concussions are more than a ‘knock to the head’. A concussion is a traumatic brain injury and the full effects are often overlooked. 

It has been estimated that only one in nine of those with symptoms of concussion report it and seek treatment (Soriano et al 2022), making public and clinical awareness of concussion critical.

With the appropriate early intervention and education, concussion symptoms can be successfully managed by physiotherapists.

A concussion is an injury that happens at a cellular level in which the axons of the neural tissue undergo shearing and stretching. 

This causes a cascade of events throughout the brain but also throughout the wider nervous system
and body.

At the initial impact—which can be either a direct contact to the head or force to the neck or torso—the axons of the brain tissue stretch and shear, interfering with the ion pumps of the cell wall. 

Sodium flows into the neurons as potassium flows out, disrupting the normal homeostatic phase of the neuron. 

The flow-on effects impact the energy levels of the neurons; to restore homeostasis, a great deal of energy (ATP) is needed. 

As a result, an energy deficit occurs in the brain, which contributes to many of the symptoms of concussion.

Following the initial injury, an inflammatory cascade occurs, triggering the microglia in the immune system. 

Microglia, which can be thought of as the ‘gatekeepers’ of the brain, protect and patrol the central nervous system, looking for any damage to the brain (Soriano et al 2022, Howell
& Southard 2022). 

It is estimated that approximately 10 per cent of the brain is made up of microglial cells so their
importance cannot be underestimated (Eyolfson et al 2020). 

Following concussion, microglial cells mobilise and signal cytokines, initiating a local inflammatory response. This response doesn’t remain local; it triggers a wider immune response that is felt throughout several systems in the body—including the gut.

Animal studies and preliminary pilot studies in humans have shown that the inflammatory cascade initiated in the brain can affect the gut microbiome (Sgro et al 2022, Aghakhani 2021, de Souza et al 2023).

As the brain triggers an inflammatory response following a concussion, the gut becomes one of the subsequent responders through an immune reaction. 

This response also leads to changes in gut permeability. 

The gut, in turn, influences inflammatory signals and contributes to changes in the central nervous system, particularly involving the autonomic nervous system (ANS) and the vagus nerve. 

This physiological loop occurs within a short window following the initial concussion.

Signs and symptoms

The process for clinical diagnosis of concussion relies heavily on clinical observation or reporting of subjective symptoms because imaging does not offer a reasonable diagnostic process (Ferry & DeCastro 2023). 

With an acute, mild traumatic brain injury, no structural changes will appear on MRI or CT. 

Loss of consciousness is also not a good indicator of concussion, with more than 90 per cent of concussion patients remaining conscious following injury (de Souza et al 2023). 

Of the subjective reported symptoms, headaches are the most common. The causes of headaches can vary in nature; they may be cervicogenic, cognitive loading or visually evoked, to name a few.

Visual disturbances are another common symptom that can be measured clinically.

In a 2023 review by de Souza et al, it was estimated that up to 69 per cent of concussion injuries present with oculomotor impairments due to disruptions in neural-vision pathways. 

Clinical testing may find that oculomotor convergence (eyes coming together during focus), accommodation (the eyes’ ability to maintain focus with a variety of distances) and the movements of the eyes are significantly disrupted following a concussion. 

These impairments can make daily tasks such as screen use, reading and driving difficult. Patients may report blurred vision, double vision, headache or a vague difficulty with focusing.

Dizziness and balance issues are also frequently observed. 

These symptoms suggest a disruption of the vestibular system. 

When they are combined with deficits in the central processing of the brain, impaired proprioception from the neck and body and visual changes, the concussed brain may struggle to complete
tasks involving quick or multi-directional movements. 

Screening for peripheral vestibular issues such as benign paroxysmal positional vertigo is essential but further testing for centralised vestibular and balance deficits is critical for a comprehensive review.

Cervical spine dysfunction is also a key consideration when managing concussion.

It is estimated that the forces needed to sustain a concussion are within 90–100 g-force (Brennan et al 2017 noted 98 g-force). 

This impact contributes to the axonal stretching and ionic changes that succeed a concussion. However,
a whiplash injury can occur with as low as four g-force. 

All concussion injuries therefore affect the cervical spine. 

Neck dysfunction can further contribute to headaches, dizziness and poor balance. So while whiplash injuries can occur without concussion, concussion injuries always have a component of whiplash.

Additional signs and symptoms to consider post-concussion include confusion, disorientation, irritability and mood changes. 

Pre-existing mental health conditions prior to the concussion increase the risk of developing mood disorders post-injury and can influence the duration of symptoms. 

Changes in the patient’s occupational and social roles as a result of the injury may also adversely affect their mental wellbeing (Auxéméry 2018).

Other complications following a concussion injury

Dysregulation of the ANS is another essential consideration when addressing concussion. 

Disrupted axonal communication, further inflammatory cascades and disturbed cerebral blood flow can create an intolerance to physical activity and exercise (Miranda et al 2018). 

The gold standard in assessing ANS regulation is the Buffalo Concussion Treadmill Test, which is used to guide exercise prescription following a concussion. 

Further return-to-play protocols can be implemented once a patient has passed a Buffalo Concussion
Treadmill Test, after which sport-specific training is key to building up tolerance.

In more severe cases, autonomic dysregulation may also manifest as postural orthostatic tachycardia
syndrome and may need a slower progression to recovery in which symptoms and heart rate variables are
closely monitored in order to slowly improve the tolerance of the sympathetic nervous system. 

Additional input to support improved vagal tone, mitigating sympathetic overdrive of the ANS, as well as education on recovery are critical in the management of a patient with postural orthostatic tachycardia
syndrome and ANS dysfunction.

Post-concussion syndrome (PCS) is also a consideration for clinicians when assessing a concussed client.

While the majority of concussion symptoms resolve in 10–14 days, it is noted that in about 10–25 per cent of the concussion population, symptoms persist over four weeks and meet the criteria for PCS (Permenter et al 2022, Rytter et al 2021, Polinder et al 2018). 

Risk factors for PCS are linked to pre-existing disorders such as migraines, mental health, poor patient
understanding of injury resolution and older populations (Rytter et al 2021). 

Clinically, subjective screening tools such as the Post-Concussion Symptom Scale are validated clinical tools that can be used to screen for the possibility of PCS when symptoms have lasted for more than four weeks.

Education and early access to assessment remain key parts of the clinical management of concussion.

Across Australia, access to concussion care is highly variable depending on state and regional access.

Therefore, telehealth can be critical in providing early education and triaging for those with a suspected concussion. 

Telehealth within one to two weeks following injury can reduce the risk of chronic symptoms, given that delayed access to assessment and education is one of several risk factors for the development of
PCS. 

Telehealth access is also an effective way for those who cannot travel due to their injury to receive early intervention and appropriate triaging as needed (Elbin et al 2022, Ellis & Russell 2019).

Concussion is not simply ‘a knock to the head’. The inflammatory effects of concussion extend beyond the brain tissue, disrupting the ANS, gut and immune system.

Symptoms of concussion can vary greatly from one person to another; a thorough and tailored clinical examination of all systems is needed to create a personalised treatment plan. 

While concussion is often regarded as a ‘mild’ injury, it is now better understood that even a mild traumatic brain injury can lead to the development of PCS or postural orthostatic tachycardia syndrome. 

In all cases of concussion, early assessment and education by an appropriately trained clinician as well as patient education on how concussion can be managed are key to mitigating symptoms and accelerating recovery.

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Dr Jessica Povall APAM has a Doctorate of Physiotherapy from Boston University, USA. Jessica has over 13 years’ experience working in the USA, New Zealand and Australia. She treats patients virtually via telehealth at drjessicapovallphysio.com and in person at Brain Hub in Sydney.