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Over the last 20 years, the evidence surrounding concussion has rapidly evolved. Once assumed to be a short-lived transient injury, it is now becoming clear that the effects of concussion (and particularly repeated concussions) likely extend beyond the short term. An increasing body of evidence suggests that following a concussion, athletes possess a higher risk of sustaining both subsequent concussions (1) and musculoskeletal injuries (2-4) in the medium term. Additionally, emerging evidence shows that there may be potential long-term impacts of repeated injuries on cognitive function, mental health and the development of neurological conditions (5-7).
"Despite not causing damage that can be seen using traditional neuroimaging tools, concussion causes a change to the way the brain is working".
Despite being one of the most common injuries seen in American Football, Ice Hockey, Wrestling, and Rugby Union (8-11), concussion is arguably the most difficult injury to manage in sport. It is a traumatic brain injury, but unlike other injuries it does not result in structural damage. Rather, concussive injuries cause a functional disturbance to the brain (12). In other words, despite not causing damage that can be seen using traditional neuroimaging tools (MRI, CT scans etc), it causes a change to the way the brain is working. What this means in practice, is that medical professionals cannot use objective tools such as MRI, CT scans or blood tests to aid diagnosis and guide recovery and return to play decisions. Rather, to detect the seemingly ‘invisible’ injury, they have to rely on traditional clinical evaluations, coupled with a battery of standardised assessment protocols.
While these consequences are broad ranging, for the purpose of this blog I am going to focus on the short-medium term implications, and how exercise professionals such as physiotherapists and strength and conditioning practitioners hold the key to improving outcomes. Specifically, I am going to introduce the current processes for managing concussion, expand on how these approaches are likely inadequate given the evidence of increased risk of injury post-concussion, and finally how technology is paving the way for making data driven management decisions.What are the current concussion management processes?
"Athletes who have sustained a concussion, are more likely to sustain a future musculoskeletal injury following return to play".
To understand how concussion is linked to an increased risk of future injury, we first need to delve into the current concussion management processes. The management of concussion can be considered under two main aspects:
The current clinical standard for the management of sports related concussion involves the identification of the signs of concussion, and where appropriate, an on field triage evaluation to assess the player’s symptoms, orientation and evaluate if any red-flags are present. If a concussion is suspected, the player is removed from play and the on-field assessment is typically followed-up in the medical room with a clinical exam.
As mentioned above, as there are no gold-standard ‘objective’ markers of concussion, this examination is supported by various assessments to evaluate the athletes functional deficits, including clinical symptoms, sensorimotor function (balance, co-ordination and reaction time) and neurocognitive function (13, 14), most commonly in the form of the Sports Concussion Assessment Tool (SCAT-5) (15).
The traditional model of concussion recovery evaluation is centred around a process called the graduated return-to-play (GRTP) protocol. In a nutshell, the GRTP is a phased process whereby after becoming asymptomatic at rest, athletes progress through six-steps which involves the gradual re-introduction of asymptomatic physical and skill based activities. While it might seem surprising to some readers, this means that the return to play of athletes is simply dictated by the length of time since the injury and the athlete reporting no symptom (13).
Despite athletes’ symptoms typically resolving within a matter of days (median = 5.92 days; IQR = 3.02 to 9.98 days) (9), there is a growing body of evidence suggesting that the consequences of concussion likely extend beyond this ‘clinical recovery’. It is now known with a high level of certainty that athletes who have sustained more than one previous concussion are at a heightened risk of sustaining future concussions (1). More recently we have learned that athletes who have sustained a concussion, are more likely to sustain a future musculoskeletal injury following return to play. McPherson and colleagues (16) conducted a meta-analysis to investigate if a history of concussion was associated with an increased risk of musculoskeletal injury. Pooling data from multiple studies consisting of a range of athletes from different sports, they identified that athletes with a history of concussion (n = 661) were at a 2.11 (95% CI 1.46 to 3.06) times greater odds of sustaining a subsequent musculoskeletal injury, compared with the control group (n = 1,757) (16).
"We identified that players with sub-optimal balance performance at baseline were at a 2.81 greater odds of sustaining a concussion during the Rugby Union season".
Emerging evidence has showed us that the association may be related to the presence of subtle sensorimotor and neurocognitive deficits which persist beyond the resolution of the traditional signs and symptoms of concussion (17). What’s more is these defects are not detected by traditional clinical assessment batteries, such as the SCAT5. In other words, disturbances in the way the brain processes its environment and controls the body’s movements likely persist beyond the point at which an individual notices that obvious symptoms (headaches, dizziness, fatigue etc) have resolved. Over the last few years, my research has focused on attempting to understand this relationship and develop clinical tools for the objective evaluation of sensorimotor control, that can be used by the average practitioner and athlete. To do so, we use the same type of inertial sensor technology used within the Output Sports system. This approach can provide the objectivity and sensitivity of laboratory based systems, while ensuring that the developed tools can be used accessibly across a range of sporting environments (18).
Over the last few years, we have established that we can instrument a clinical balance test called the Y Balance Test using a single inertial sensor on the lumbar spine and measure control of movement during the dynamic movements, reliably (19) and validly (20-22). The development of this tool, called the Quantified Y Balance Test (QYBT) laid the groundwork for a series of clinical studies which investigated the relationship between concussion, sensorimotor control and injury risk. In a cross-sectional study consisting of 146 NCAA Division one American Football and Ice Hockey athletes, we demonstrated that those with a history of one or more concussions within the last two years (median 294 days since injury; range 81 to 717) possessed dynamic balance deficits, when compared to healthy control athletes – suggesting inadequate sensorimotor recovery post-injury (23). Conversely, athletes whose injury occurred greater than two years ago (median 1,306 days since injury; range 820 to 3,853) possessed comparable performance to the healthy controls – suggesting full sensorimotor recovery. We have also recently shown similar findings in 195 adolescent Rugby Union athletes; highlighting that those with a history of concussion had persistent deficits, when compared to healthy control athletes (24). Importantly, the QYBT based measures of performance captured deficits which where were not reflected by the traditional clinical balance component (mBESS) of the SCAT5. The implications of this research become clear when you consider that poor sensorimotor control is a known risk factor for many injuries, such as anterior cruciate ligament (25, 26) and lateral ankle sprains (27).
Figure 1: QYBT performance
In an attempt to further untangle the complex relationship between movement and concussion-risk, we undertook an exploratory prospective study to investigate the link between baseline dynamic balance performance and subsequent concussive injury (28). We tested the balance performance of a cohort of 109 elite Rugby Union players during the pre-season using the QYBT. We then followed these athletes over the course of the season to identify those who went on to sustain a concussion. We identified that players with sub-optimal balance performance at baseline were at a 2.81 greater odds (95% CI = 1.02-7.74) of sustaining a concussion during the Rugby Union season, than those with optimal balance performance. This remained, even when statistically controlling for concussion history, playing position or age. Essentially, what these findings indicate is that there is a link between sensorimotor performance and risk of concussion in Rugby Union athletes. While this was the first study to identify a discrete measure of dynamic balance performance as a modifiable risk-factor for sport-related concussion, we are currently in the process of validating these findings in adolescent and professional rugby athletes in collaborations with the University of Ulster and ASM Clermont Auvergne, respectively.
The practical implications of my research are always at the forefront of my mind. To help bridge the gap between research and practice, we recently conducted a study whereby elite Rugby Union, American Football and Ice Hockey athletes were baseline tested during the pre-season using the QYBT (29). These athletes were then followed over the course of the season to identify if they suffered a concussion. In those that sustained a concussion (17 athletes), we then evaluated their performance 24-48 hours post-injury and at the point of returning to full contact training. We also re-tested a group (20 athletes) who did not sustain any injury 6-months later to act as a ‘healthy’ control group. What we found was that the athletes who sustained a concussion demonstrated significant balance deficits 24-48 hours post-injury, which were also associated with the length of time to return to play. In other words, balance was impaired post-injury and those with worse performance 24-48 hours post-injury were more likely to have a longer time to return to play. What’s interesting is that while some athletes had returned to baseline levels of performance at return to play, others had persistent deficits, some of which exceeded the measurement error for the QYBT. While we have yet to thoroughly investigate the link between these post-injury deficits and future injury, based on the well established link between sensorimotor control and injury risk, these deficits would likely put these athletes at an increased risk of future injury (25-27).
The figure below presents real world data from three athletes from the above study, comparing the different recovery trajectories of two concussed athletes, and comparing them to a third un-injured athlete. We have developed a way to represent the QYBT performance in an easy to understand manner, characterising each athletes performance as a percentile of a large database of over 600 individuals. This example highlights how objective data could be used on an individual level to quantify an athlete’s balance performance, compare it to their pre-injury performance and leverage it as part of a wider multifactorial battery of assessments to guide the return to play process. In these cases, both athletes had ‘clinically recovered’ and the traditional SCAT-5 balance test (mBESS) did not capture any deficits. Despite this, from the QYBT performance it is clear that athlete-1 would likely benefit from some additional targeted rehabilitation throughout the return to play process. This would aim to ensure that at the point at which they returned to play, any residual deficits that may boost their risk of future injury have been mitigated.
Figure 2: QYBT performance in two concussed athletes (1 & 2), and one healthy control athlete (3).
“The current approach of relying on subjective symptom rating and time since injury to guide return to play decisions are not fit for purpose".
As outlined above, it is becoming clearer that the effects of concussion extend long beyond what we deem ‘clinical recovery’ and that the current approach of relying on subjective symptom rating and time since injury to guide return to play decisions are not fit for purpose. Fundamentally, I believe we need to move beyond the blunt clinical tools such as the SCAT5 and develop comprehensive return to play assessment batteries which incorporate technology, where appropriate. While I have focused on sensorimotor control, concussion leads to a broad range of impairments. Therefore, it is key that these tools are multi-factorial and also evaluate aspects of cognitive and behavioural function, across multiple time-points during the recovery process. It is clear that sports and exercise professionals should be working alongside medical colleagues to help develop and implement these comprehensive protocols, based on the evidence which is rapidly emerging to ensure that our athletes are receiving the most up-to-date and advance care. For those interested, my colleagues and I have previously shared some thoughts on this approach here.
To help progress this forward, technology based systems like Output Sports are key, providing tools for practitioners to easily collect valid and reliable movement data. These data, when viewed alongside additional cognitive and behavioural information can be used to objectively quantify an athlete’s performance at a healthy baseline, and as they progress through the acute injury and return to play procedures. Instead of simply relying on the time since injury and subjective symptoms, practitioners and athletes can use objective data to help guide decision making. This can then inform what additional rehabilitation approaches may complement the graduated return to play procedure, with the view to minimising the medium to long-term consequences of concussion.
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Dr. William Johnston is a physiotherapist and clinical researcher in the area of Digital Health at the Insight Centre for Data Analytics, University College Dublin. Working at the nexus of healthcare & technological innovation in an industry facing research centre, William has a deep understanding of how validated technology, coupled with rigorous quantitative & qualitative research, can be used to disrupt & improve modern health, wellness and performance. He is interested in bridging the gap between digital health research and clinical practice, accelerating the rate at which validated technology can be used by clinicians and patients.
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