Cumulative head impact burden in high school football

Subconcussive head impact biomechanics: comparing differing offensive schemes

PURPOSE

Recent literature suggests that subconcussive impacts may influence cognitive functioning across the life span. These effects are suggested to manifest as functional and possibly structural changes. Head impact biomechanics during American football have been characterized from the high school to professional level, but style of play has not been considered. The aim of this investigation was to quantify and compare head impact frequencies and magnitudes between two different offensive schemes.

METHODS

We investigated the frequencies and magnitudes (linear acceleration [g], rotational acceleration [rad·s], and HITsp) of head impacts sustained by 83 high school football athletes, playing for schools using two different offensive schemes. The two schemes comprised a run-first offense (42 athletes) and a pass-first offense (41 athletes). The Head Impact Telemetry System was used to record head impact measures.

RESULTS

A total of 35,620 impacts were recorded across two seasons. Athletes in the run-first offense sustained an average of 456 head impacts per season (41 practices and 9 games), whereas the pass-first offense athletes sustained an average of 304 head impacts per season (44 practices and 9 games). The pass-first offense, however, sustained significantly higher impact magnitudes (P values < 0.05; 28.56g, 1777.58 rad·s, and 16.24) than the run-first offense (25.67g, 1675.36 rad·s, and 15.48) across a season.

CONCLUSIONS

These data provide a first look at how different offensive strategies may influence head impact exposure in football athletes. In the study population, a run-first offense was associated with more frequent head impacts, of smaller magnitude, than a pass-first offense.

Role of subconcussion in repetitive mild traumatic brain injury

Research now suggests that head impacts commonly occur during contact sports in which visible signs or symptoms of neurological dysfunction may not develop despite those impacts having the potential for neurological injury. Recent biophysics studies utilizing helmet accelerometers have indicated that athletes at the collegiate and high school levels sustain a surprisingly high number of head impacts ranging from several hundred to well over 1000 during the course of a season. The associated cumulative impact burdens over the course of a career are equally important. Clinical studies have also identified athletes with no readily observable symptoms but who exhibit functional impairment as measured by neuropsychological testing and functional MRI. Such findings have been corroborated by diffusion tensor imaging studies demonstrating axonal injury in asymptomatic athletes at the end of a season. Recent autopsy data have shown that there are subsets of athletes in contact sports who do not have a history of known or identified concussions but nonetheless have neurodegenerative pathology consistent with chronic traumatic encephalopathy. Finally, emerging laboratory data have demonstrated significant axonal injury, blood-brain barrier permeability, and evidence of neuroinflammation, all in the absence of behavioral changes. Such data suggest that subconcussive level impacts can lead to significant neurological alterations, especially if the blows are repetitive. The authors propose “subconcussion” as a significant emerging concept requiring thorough consideration of the potential role it plays in accruing sufficient anatomical and/or physiological damage in athletes and military personnel, such that the effects of these injuries are clinically expressed either contemporaneously or later in life.

Prevalence and characterization of mild cognitive impairment in retired national football league players

It has been hypothesized that exposure to repetitive head trauma from contact sports over a long-playing career may eventuate in an increased risk of late-life cognitive impairment. There are currently two competing hypotheses about the possible mechanism underlying such impairment. One is the presence of a unique neurodegenerative disorder known as ‘‘chronic traumatic encephalopathy’’ (CTE). The other is diminished cerebral reserve leading to the earlier clinical expression of age-related neurodegenerative diseases such as mild cognitive impairment (MCI) and Alzheimer’s disease(AD). The present study examined informant AD8 inventory data in a sample of 513 retired National Football League(NFL) players. These data were indicative of possible cognitive impairment in 35.1% of this relatively young sample. A comparison of neurocognitive profiles in a subsample of this group to a clinical sample of patients with a diagnosis of MCI due to AD revealed a highly similar profile of impairments. Overall, the data suggest that there may be an increased prevalence of late-life cognitive impairment in retired NFL players, which may reflect diminished cerebral reserve. The findings are considered preliminary, but emphasize the need for larger, controlled studies on this issue.

Head impact exposure in youth football: high school ages 14 to 18 years and cumulative impact analysis

Sports-related concussion is the most common athletic head injury with football having the highest rate among high school athletes. Traditionally, research on the biomechanics of football-related head impact has been focused at the collegiate level. Less research has been performed at the high school level, despite the incidence of concussion among high school football players. The objective of this study is to twofold: to quantify the head impact exposure in high school football, and to develop a cumulative impact analysis method. Head impact exposure was measured by instrumenting the helmets of 40 high school football players with helmet mounted accelerometer arrays to measure linear and rotational acceleration. A total of 16,502 head impacts were collected over the course of the season. Biomechanical data were analyzed by team and by player. The median impact for each player ranged from 15.2 to 27.0 g with an average value of 21.7 (±2.4) g. The 95th percentile impact for each player ranged from 38.8 to 72.9 g with an average value of 56.4 (±10.5) g. Next, an impact exposure metric utilizing concussion injury risk curves was created to quantify cumulative exposure for each participating player over the course of the season. Impacts were weighted according to the associated risk due to linear acceleration and rotational acceleration alone, as well as the combined probability (CP) of injury associated with both. These risks were summed over the course of a season to generate risk weighted cumulative exposure. The impact frequency was found to be greater during games compared to practices with an average number of impacts per session of 15.5 and 9.4, respectively. However, the median cumulative risk weighted exposure based on combined probability was found to be greater for practices vs. games. These data will provide a metric that may be used to better understand the cumulative effects of repetitive head impacts, injury mechanisms, and head impact exposure of athletes in football.

An overview of the basic science of concussion and subconcussion: where we are and where we are going

There has been a growing interest in the diagnosis and management of mild traumatic brain injury (TBI), or concussion. Repetitive concussion and subconcussion have been linked to a spectrum of neurological sequelae, including postconcussion syndrome, chronic traumatic encephalopathy, mild cognitive impairment, and dementia pugilistica. A more common risk than chronic traumatic encephalopathy is the season-ending or career-ending effects of concussion or its mismanagement. To effectively prevent and treat the sequelae of concussion, it will be important to understand the basic processes involved. Reviewed in this paper are the forces behind the primary phase of injury in mild TBI, as well as the immediate and delayed cellular events responsible for the secondary phase of injury leading to neuronal dysfunction and possible cell death. Advanced neuroimaging sequences have recently been developed that have the potential to increase the sensitivity of standard MRI to detect both structural and functional abnormalities associated with concussion, and have provided further insight into the potential underlying pathophysiology. Also discussed are the potential long-term effects of repetitive mild TBI, particularly chronic traumatic encephalopathy. Much of the data regarding this syndrome is limited to postmortem analyses, and at present there is no animal model of chronic traumatic encephalopathy described in the literature. As this arena of TBI research continues to evolve, it will be imperative to appropriately model concussive and even subconcussive injuries in an attempt to understand, prevent, and treat the associated chronic neurodegenerative sequelae.

Lack of long-term fMRI differences after multiple sports-related concussions

INTRODUCTION

Mild traumatic brain injury (mTBI) or concussion has been acutely associated with several cognitive symptoms, including deficits in response inhibition, working memory and motor performance. The pervasiveness of these cognitive symptoms has been more controversial. The effects of multiple concussions on neuropsychological functioning and brain activation following at least 6-months post-mTBI were examined.

METHODS

Twenty right-handed male athletes with a history of at least two concussions and 20 age/pre-morbid IQ/athletic-experience matched controls underwent neuropsychological assessment and fMRI scanning where they performed versions of a colour-word Stroop interference task, an operation-span working memory task and a finger-tapping task.

RESULTS

The Attention index score on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was lower for the concussion group, but only at liberal statistical threshold. Total RBANS score approached statistical significance. Reaction time during neurobehavioural tasks was similar across groups, but accuracy was reduced in the concussed group on the working memory task. Despite expected activation patterns within each group, there were no group differences in neural activation on any functional tasks using either whole-brain or ROI-specific analyses at liberal statistical thresholds.

CONCLUSION

There were minimal differences between the two closely matched groups. Results point to the relative plasticity of younger adults' cognitive abilities following concussion.

Military- and sports-related mild traumatic brain injury: clinical presentation, management, and long-term consequences

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Intensity- and interval-specific repetitive traumatic brain injury can evoke both axonal and microvascular damage

In the experimental setting several investigators have recently reported exacerbations of the burden of axonal damage and other neuropathological changes following repetitive traumatic brain injuries (TBI) that were sustained at intervals from hours to days following the initial insult. These same studies also revealed that prolonging the interval between the first and second insult led to a reduction in the burden of neuropathological changes and/or their complete elimination. Although demonstrating the capability of repetitive TBI to evoke increased axonal and other neuropathological changes, these studies did not address the potential for concomitant microvascular dysfunction or damage, although vascular dysfunction has been implicated in the second-impact syndrome. In this study we revisit the issue of repetitive injury in a well-controlled animal model in which the TBI intensity was bracketed from subthreshold to threshold insults, while the duration of the intervals between the injuries varied. Employing cranial windows to assess vascular reactivity and post-mortem amyloid precursor protein (APP) analysis to determine the burden of axonal change, we recognized that subthreshold injuries, even when administered in repeated fashion over a short time frame, evoked neither axonal nor vascular change. However, with an elevation of insult intensity, repetitive injuries administered within 3-h time frames caused dramatic axonal damage and significant vascular dysfunction bordering on a complete loss of vasoreactivity. If, however, the interval between the repetitive injury was extended to 5 h, the burden of axonal change was reduced, as was the overall magnitude of the ensuing vascular dysfunction. With the extension of the interval between injuries to 10 h, neither axonal nor vascular changes were found. Collectively, these studies reaffirm the existence of significant axonal damage following repetitive TBI administered within a relatively short time frame. Additionally, they also demonstrate that these axonal changes parallel changes in the cerebral microcirculation, which also may have adverse consequences for the injured brain.

Comparative analysis of state-level concussion legislation and review of current practices in concussion

Object

Forty-two states and the District of Columbia have passed legislation based on the Lystedt law of Washington state, enacted in 2009 to protect young athletes who have sustained a concussion. The aim of this study was to note the several similarities and differences among the various laws.

Methods

Concussion legislation was compared for 50 states and the District of Columbia. Evaluation parameters of this study included stipulations of concussion education, criteria for removal from play, requirements for evaluation and return to play after concussion, and individuals required to assess young athletes. Other parameters that were not consistent across states were also noted.

Results

Forty-three states and the District of Columbia have passed concussion legislation, and an additional 4 states have pending legislation. All states with existing legislation support concussion education for coaches; however, only 48% require coaches to undergo formal education. Athletes must be educated on concussion in 86% of states and parents in 88.7%. Suspicion of concussion is a criterion for removal from play in 75% of states; signs and symptoms of concussion are criteria for removal from play in 16% of states. The individuals allowed to evaluate and clear an athlete for return to play differ greatly among states.

Conclusions

Injury prevention legislation holds historical precedent, and given the increasing attention to long-term sequelae of repeated head trauma and concussion, concussion legislation has been rapidly passed in 43 states and the District of Columbia. Although the exact stipulations of these laws vary among states, the overall theme is to increase recognition of concussion in young athletes and ensure that they are appropriately cleared for return to play after concussion.

Epidemiology, trends, assessment and management of sport-related concussion in United States high schools

PURPOSE OF REVIEW

Sport-related concussion affects athletes at every level of participation. The short and long-term effects of concussions that occur during childhood and adolescence are not fully understood. The purpose of this review is to describe the current burden of disease, current practice patterns and current recommendations for the assessment and management of sport-related concussions sustained by United States high school athletes.

RECENT FINDINGS

Millions of high school students participate in organized sports in the United States. Current estimates suggest that, across all sports, approximately 2.5 concussions occur for every 10 000 athletic exposures, in which an athletic exposure is defined as one athlete participating in one game or practice. At schools that employ at least one athletic trainer, most high school athletes who sustain sport-related concussions will be cared for by athletic trainers and primary care physicians. Approximately 40% will undergo computerized neurocognitive assessment.

SUMMARY

The number of high school athletes being diagnosed with sport-related concussions is rising. American football has the highest number of concussions in high school with girls' soccer having the second highest total number. Fortunately, coaches are becoming increasingly aware of these injuries and return-to-play guidelines are being implemented.

Field-based measures of head impacts in high school football athletes

PURPOSE OF REVIEW

Recent technological advances have allowed the in-vivo measurement of impacts sustained to the head during helmeted sports. These measurements are of interest to researchers and clinicians for their potential to understand both the underlying mechanics of concussive injuries and the potential for real-time injury diagnostics. Following an overview of impact biomechanics, this review will evaluate the following: in-vivo technology being used in American football players; impact frequencies and magnitudes; and the biomechanical threshold for concussion.

RECENT FINDINGS

The average high school athlete sustains over 650 impacts in a season, and the level at which concussion occurs is approximately 100  g and 5500  rad/s/s.

SUMMARY

High school athletes sustain a significant number of head impacts each year. The impacts are similar in both volume and magnitude when compared with collegiate athletes. The magnitude of impact that results in concussion is also the same at both levels of play, although the collegiate athlete may have a higher injury tolerance.

Post-concussion cognitive declines and symptomatology are not related to concussion biomechanics in high school football players

Concussion is a major public health concern with nearly 4 million injuries occurring each year in the United States. In the acute post-injury stage, concussed individuals demonstrate cognitive function and motor control declines as well as reporting increased symptoms. Researchers have hypothesized that the severity of these impairments is related to impact magnitude. Using the Head Impact Telemetry System (HITS) to record head impact biomechanics, we sought to correlate pre- and post-concussive impact characteristics with declines in cognitive performance and increases in concussion-related symptoms. Over four seasons, 19 high school football athletes wearing instrumented helmets sustained 20 diagnosed concussions. Each athlete completed a baseline computer-based symptom and cognitive assessment during the pre-season and a post-injury assessment within 24 h of injury. Correlational analyses identified no significant relationships between symptoms and cognitive performance change scores and impact biomechanics (i.e., time from session start until injury, time from the previous impact, peak linear acceleration, peak rotational acceleration, and HIT severity profile [HITsp]). Nor were there any significant relationships between change scores and the number of impacts, cumulative linear acceleration, cumulative rotational acceleration, or cumulative HITsp values associated with all impacts prior to or following the injury. This investigation is the first to examine the relationship between concussion impact characteristics, including cumulative impact profiles, and post-morbid outcomes in high school athletes. There appears to be no association between head impact biomechanics and post-concussive outcomes. As such, the use of biomechanical variables to predict injury severity does not appear feasible at this time.