Journal of Concussion

‘WARNING: motor sport can be dangerous’. The spectrum of head injuries in motor sport has shifted dramatically in recent decades, fuelled by advances in medicine and engineering. Despite these successes, there are growing public and professional concerns regarding concussion in motor sport. This review appraises the published literature concerning concussion in motor sport, with particular focus on the current medical and technical challenges in the field. The incidence and assessment of concussion in motor sport is discussed, in addition to modifiable risk factors within and outside the automobile environment. Lastly, areas for further research and development are outlined.

Traumatic brain injury and the long-term consequences of repeated concussions constitute mounting concerns in the United States, with 5.3 million individuals living with a traumatic brain injury-related disability. Attempts to understand mechanisms and possible therapeutic approaches to alleviate the consequences of repeat mild concussions or traumatic brain injury on cerebral vasculature depend on several aspects of the trauma, including: (1) the physical characteristics of trauma or insult that result in damage; (2) the time “window” after trauma in which neuropathological features develop; (3) methods to detect possible breakdown of the blood–brain barrier; and (4) understanding different consequences of a single concussion as compared with multiple concussions. We review the literature to summarize the current understanding of blood–brain barrier and endothelial cell changes post-neurotrauma in concussions and mild traumatic brain injury. Attention is focused on concussion and traumatic brain injury in humans, with a goal of pointing out the gaps in our knowledge and how studies of rodent model systems of concussion may help in filling these gaps. Specifically, we focus on disruptions that concussion causes to the blood–brain barrier and its multifaceted consequences. Importantly, the magnitude of post-concussion blood–brain barrier dysfunction may influence the time course and extent of neuronal recovery; hence, we include in this review comparisons of more severe traumatic brain injury to concussion where appropriate. Finally, we address the important, and still unresolved, issue of how best to detect possible breakdown in the blood–brain barrier following neurotrauma by exploring intravascular tracer injection in animal models to examine leakage into the brain parenchyma.

Cognitive impairment is a common symptom of mild traumatic brain injury (mTBI) and can have long term cognitive and behavioral consequences. Despite this, there is no universally accepted protocol for assessment of cognition in this population. Conventional neuropsychological assessment tools rely on verbal or manual responses which lend themselves to confounding factors such as stress, intelligence, initiation, and motivation, suggesting the need for more objective tools. A scoping review was undertaken to explore the utility of eye-tracking methods for detecting cognitive impairment in mTBI patients, and to survey the kinds of tasks used in this context. Six academic databases were searched for studies related to brain injury, eye tracking, and cognition. Data from 17 articles were extracted and synthesized. In most cases, neuropsychological and eye-tracking methods were in accordance when detecting cognitive impairment. However, in many cases, eye-tracking measures detected impairments when neuropsychological tasks did not. This review suggests that eye tracking could provide an effective, objective method to measure cognitive impairment in mTBI.

Often the Balance Error Scoring System (BESS) is used to assess balance during a clinical evaluation of a patient presenting with mild Traumatic Brain Injury (mTBI). Although recent research has shown the benefits of using inertial sensor measures such as the Root Mean Square (RMS) of the acceleration in place of clinical scoring, few normative data are available for clinicians to reference. The purpose of this paper was to provide normative data collected using wearable sensors for healthy controls across three age groups, as well as providing cohort data for mTBI participants across three stages following injury (acute, sub-acute and chronic). The RMS in the Medio-Lateral direction (ML RMS sway) of each condition (double stance – DS; single stance – SS; and tandem stance – TS) was extracted per participant for analysis. The average ML RMS sway across all conditions was also calculated (ML RMS-Av). Percentiles were calculated to provide normative data, and two multivariate general linear models were used to evaluate differences between 1) non-athlete controls, athlete controls, and athletes with acute mTBI, and 2) non-athletic cohorts of control, sub-acute and chronic mTBI groups across young, middle-aged, and older adults. Model 1 revealed athletes with acute mTBI had more ML RMS sway than athlete controls the for the DS condition (p < 0.001), but no differences with non-athlete controls. Athlete controls also had less ML RMS sway for the SS condition and ML RMS-Av (p ≤ 0.022) compared with non-athlete controls. Model 2 revealed less ML RMS sway in the control group than the sub-acute and chronic mTBI groups for DS (p ≤ 0.004), but no differences between the sub-acute and chronic group, while more ML RMS sway occurred in the chronic group compared with the control and sub-acute groups for the TS condition and ML RMS-Av (p ≤ 0.013). Older adults had more ML RMS sway than young and middle-aged adults for SS, TS and ML RMS-Av (p ≤ 0.019), while there were no differences between the young and middle-aged adults. Normative values presented here can help increase the practical application of instrumented balance assessment of mTBI patients through wearable sensors. ML RMS sway in the DS condition provided the clearest distinction between control and mTBI groups, but we caution that young adult athletes need to be assessed against athletic peers in the absence of baseline normative values. In non-athlete cohorts, age and gender norms may not be necessary to consider when assessing DS performance; however, age may be an important factor to consider when accessing norms for other stance conditions or the average performance across all conditions.

Video analysis of situational factors associated with head impacts and concussion has been completed in several sports, however has yet to be completed in cricket. This study aimed to identify situational factors associated with concussion in elite Australian male and female cricket. Match video of head impacts were coded for player position, impacting object, source of ball, location of impact, and where the ball went after impact. Head impacts were then categorised as either concussion or no concussion based on clinical diagnosis. Data for 197 head impacts included 35 (18%) which were diagnosed as concussion. Head impacts typically occurred to an on-strike batter facing a pace bowler (84%). If the ball stopped or rebounded towards the source, 21% were diagnosed as concussion (13% if the ball deflected away from the source). If impact was to an unprotected head, 38% were diagnosed as concussion (16% if impact was to a helmet). If impact was to the back of the helmet or head, 40% were diagnosed as concussion (11–21% for other areas of the head or helmet). The combination of situational factors most consistent with concussion were impact from ball that hit the back of helmet or head and stopped or rebounded towards the source (PPV 80%, p = 0.002). Consideration of the situational factors of a head impact may improve the speed and accuracy of clinical decision making on whether to remove a player from the field for further assessment, particularly if clinical signs are unclear. Video may be used as a tool to support this process. Improved impact attenuation of cricket helmets, particularly at the back, may reduce the risk of concussion.

The Sports Concussion Assessment Tool 3rd version is a sports screening tool that is often used to support return to play decisions following a head injury. The Sports Concussion Assessment Tool 3rd version is presumed to identify brain dysfunction (implying a degree of brain injury); however, the Sports Concussion Assessment Tool has never been validated with patients with definite acute brain injury. In this study, we found that all three Sports Concussion Assessment Tool 3rd version domains – symptoms, cognitive and balance assessments – were sensitive in discriminating traumatic brain injury patients (all with abnormal acute neuroimaging) from healthy controls. Through a correlation matrix (Bonferroni corrected), we found no correlation between the subjective (symptoms) and objective (examination) Sports Concussion Assessment Tool 3rd version assessments, e.g. complaints of imbalance and memory dysfunction were not correlated, respectively, with performance on testing balance and memory function. When relaxing the correction for multiple comparisons we found that of all Sports Concussion Assessment Tool 3rd version symptoms, a feeling of ‘pressure in the head’ had the largest number of co-correlations (including affective symptoms) and overwhelmingly in a pattern indicative of migraine. Taken together, that objective and subjective assessments in the Sports Concussion Assessment Tool 3rd version are poorly correlated, could suggest that symptoms in the Sports Concussion Assessment Tool 3rd version poorly reflect brain injury but rather indicate non-brain injury processes such as migraine. It follows that the current prominent orthodoxy of resting athletes following a head injury until their symptoms settle for fear of exacerbating brain injury may be unfavourable for their recovery – at least in some cases. Prospective clinical studies would be required to assess patient recovery from concussion with early active investigation and treatment versus rest – a notion supported by recent international consensus.

There is an unquestionable need for quantitative biomarkers of mild traumatic brain injuries. Something that is particularly true for adolescents – where the recovery from these injuries is still poorly understood. However, within this population, it is clear that the vasculature is distinctly affected by a mild traumatic brain injury. In addition, our group recently demonstrated how that effect appears to show a progression of alterations similar but in contrast to that found in severe traumatic injuries. Through measuring an adolescent population with transcranial Doppler ultrasound during a hypercapnia challenge, multiple phases of hemodynamic dysfunction were suggested. Here, we create a generalized model of the hemodynamic responses by fitting a set of inverse models to the dominant features from that work. The resulting model helps define the multiple phases of hemodynamic recovery after a mild traumatic brain injury. This can eventually be generalized, potentially providing a diagnostic tool for clinicians tracking patient’s recovery, and ultimately, resulting in more informed decisions and better outcomes.

When the human head is subjected to blunt force impact, there are several mechanical responses that may result from the forces involved, including absorption of impact forces through the various layers of the head. The purpose of this study was to develop an anatomical head model to measure force transfer through the various head layers and their displacement when subject to short-duration high-velocity impacts. An anatomical head model was constructed using previously validated simulant materials: epoxy resin (skull), polyvinyl siloxane (scalp), agar/glycerol/water (brain) and modified intravenous fluid for the cerebrospinal fluid. An array of accelerometers (4 mm × 4 mm × 1.45 mm) was incorporated into the various layers of the head to measure forces in x- (anterior/posterior), y- (left/right) and z- (up/down) axis. All sensors were connected to a signal conditioning board and USB powered data loggers. The head model was placed into a rigid metal stand with an optical sensor to trigger data capturing. A weight (750 g) was dropped from a height of 0.5 m (n= 20). Impact forces (z-axis) of 1107.05 N were recorded on top of the skin, with decreasing values through the different layers (bottom of skin 78.48 N, top of skull 319.82 N, bottom of skull 87.30 N, top and centre of brain 47.09 N and base of brain 78.41 N. Forces in the x- and y-axes were similar to those of the z-axis. With the base of the brain still receiving 78.41 N, this highlights the potential danger of repetitive impact forces to the head. Upon impact the layers of the head are displaced in the x-, y- and z-direction, with the highest values shown in the z-axis. In conclusion, this study identified the importance of considering short-duration high-intensity impacts to the head and their effect on underlying tissues.

Currently, there is a lack of clear, “gold standard” guidelines for the identification and management of sports-related concussion. This is of concern considering the importance of preventing further injury during game-play. Moreover, a number of assessment measures and tools aim to detect concussion in athletes and help inform return to play decisions, including the assessment of posture and balance, eye-saccades, memory, attention, orientation and post-concussive symptomatology. However, they have often not been widely disseminated for validity studies, and their utility or sensitivity in detecting concussion is limited due to a number of factors. As such, this review will examine current guidelines and sideline assessments measures which aim to inform decisions about return to play following sports-related concussion.

Many head trauma patients who present with prolonged post-concussion symptoms do not meet the American Congress of Rehabilitation Medicine (ACRM) diagnostic criteria for mild traumatic brain injuries (mTBI). This population has not been extensively studied and its clinical characteristics are currently uncertain. A retrospective chart review was conducted to explore the symptomatic differences between mTBI and non-mTBI head trauma patients presenting at a concussion clinic with chronic post-concussion symptoms (PCSx). Patient information was extracted from 161 charts, of which 128 subjects met the ACRM criteria for mTBI (ACRM + PCSx), while 33 did not (non-ACRM + PCSx). These two groups were compared for demographic variables and symptomology. This study found that 20.5% of subjects presenting with chronic post-concussion symptoms do not meet ACRM criteria. No symptom-specific differences were found between the two populations in any of the categories tested. These results show that chronic post-concussion symptoms are similar in both mTBI and non-mTBI head trauma patients in the general population, suggesting a need for further research focusing on this group.

Concussions are associated with an array of physical, emotional, cognitive, and sleep symptoms at multiple timescales. Cognitive recovery occurs relatively quickly – five-to-seven days on average. Yet, recent evidence suggests that some neurophysiological changes can be identified one year after a concussion. To that end, we examine more nuanced patterns in cognitive tests to determine whether cognitive abilities could identify a concussion within one-year post injury. A radial-basis (non-linear boundary) support vector machine classifier was trained to use cognitive performance measures to distinguish participants with no prior concussion from participants with prior concussion in the past year. After incorporating only 10 cognitive measures, or all 5 composite measures from the neurocognitive assessment (Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT)), over 90% accuracy was achieved in identifying both participants without prior concussions and participants with concussions in the past year, particularly when relying on non-linear patterns. Notably, classification accuracy stayed relatively constant between participants who had a concussion early or late in the one-year window. Thus, with substantial accuracy, a prior concussion can be identified using a non-linear combination of cognitive measures. Cognitive effects from concussion linger one-year post-injury, indicating the importance of continuing to follow concussion patients for many months after recovery and to take special note of constellations of cognitive abilities.