Chronic traumatic encephalopathy neuropathology might not be inexorably progressive or unique to repetitive neurotrauma.

In the 20th century, chronic traumatic encephalopathy (CTE) was conceptualized as a neurological disorder affecting some active and retired boxers who had tremendous exposure to neurotrauma. In recent years, the two research groups in the USA who have led the field have asserted definitively that CTE is a delayed-onset and progressive neurodegenerative disease, with symptoms appearing in midlife or decades after exposure. Between 2005 and 2012 autopsy cases of former boxers and American football players described neuropathology attributed to CTE that was broad and diverse. This pathology, resulting from multiple causes, was aggregated and referred to, in toto, as the pathology 'characteristic' of CTE. Preliminary consensus criteria for defining the neuropathology of CTE were forged in 2015 and published in 2016. Most of the macroscopic and microscopic neuropathological findings described as characteristic of CTE, in studies published before 2016, were not included in the new criteria for defining the pathology. In the past few years, there has been steadily emerging evidence that the neuropathology described as unique to CTE may not be unique. CTE pathology has been described in individuals with no known participation in collision or contact sports and no known exposure to repetitive neurotrauma. This pathology has been reported in individuals with substance abuse, temporal lobe epilepsy, amyotrophic lateral sclerosis, multiple system atrophy, and other neurodegenerative diseases. Moreover, throughout history, some clinical cases have been described as not being progressive, and there is now evidence that CTE neuropathology might not be progressive in some individuals. Considering the current state of knowledge, including the absence of a series of validated sensitive and specific biomarkers, CTE pathology might not be inexorably progressive or specific to those who have experienced repetitive neurotrauma.

Consent, capacity and compliance in concussion management: cave ergo medicus (let the doctor beware).

While the acute effects of concussion and mild traumatic brain injury (TBI) are well understood, the certainty in the medical literature regarding the long-term outcomes of sports-related concussion is limited. Long-term deficits that may result from single, repeated concussions, and possibly subconcussive impacts, include cognitive dysfunction, depression and executive dysfunction. Perhaps most troublingly, repetitive head impacts have been linked to neurodegenerative diseases, including chronic traumatic encephalopathy (CTE), although the precise risk of long-term consequences remains unknown. CTE represents a distinct tauopathy with an unknown incidence in athletic populations; however, a cause and effect relationship has not yet been demonstrated between CTE and concussions or between CTE and exposure to contact sports, as no prospective longitudinal studies have been performed to address that question. Studies of high-school sports exposure and long-term outcomes have not demonstrated consistent findings.Medical advice regarding return to play and the risk of acute and/or long-term consequences is therefore problematic. It is important that the individual's right to make their own choices regarding their health is respected. Team, coach, parental, peer or financial pressures should not influence this decision. The choice to return to play after a concussion or mild TBI injury is the athlete's decision once they have (1) recovered from their injury and have the legal capacity to make an informed decision; (2) been medically assessed and (3) been informed of any possible long-term risks in a language that they can understand.Given the current lack of certainty in relation to long-term outcomes from concussion, is it possible to provide a framework to inform players of current evidence, as part of a consent process, even if the information upon which the decision to return to sport is based remains uncertain and evolving?

Developing common demographic data elements to include in future editions of the SCAT and Child SCAT: a modified international Delphi study.

BACKGROUND: The Sport Concussion Assessment Tool (SCAT) and Child SCAT are the 'gold standard' assessment tools for a suspected sport-related concussion (SRC). A number of 'modifiers' (eg, previous history of concussion) of a SRC have been identified. These may influence how the SCAT/Child SCAT results should be interpreted. OBJECTIVES: To achieve consensus, via an international panel of SRC experts, on which athlete/player and parent/caregiver demographic variables should be considered for inclusion in future editions of the SCAT/Child SCAT respectively. METHODS: A two-round modified Delphi technique, overseen by a steering committee, invited 41 panellists to achieve expert consensus (≥80% agreement). The first round utilised open questions to generate demographic variables; the second round used a five-point ordinal item to rank the importance of including each variable in future editions of the SCAT/Child SCAT. RESULTS: 15 experts participated in at least one Delphi round. 29 athlete/player and eight parent/caregiver variables reached consensus for inclusion in the SCAT, whereas two parent/caregiver variables reached consensus for exclusion. 28 athlete/player and four parent/caregiver variables reached consensus for the Child SCAT, whereas two parent/caregiver variables reached consensus for exclusion. Key categories of variables included the following: concussion/sport details, personal medical conditions and family medical history. CONCLUSION: This study provides a list of athlete/player and parent/caregiver demographic variables that should be considered in future revisions of the SCAT/Child SCAT. By considering (and ultimately likely including) a wider and standard set of additional demographic variables, the Concussion in Sport experts will be able to provide clinicians and researchers with data that may enhance interpretation of the individual's data and the building of larger datasets.

Anger and Depression in Middle-Aged Men: Implications for a Clinical Diagnosis of Chronic Traumatic Encephalopathy.

OBJECTIVE: In recent years, it has been proposed that problems with anger control and depression define clinical features of chronic traumatic encephalopathy (CTE). The authors examined anger problems and depression in middle-aged men from the general population and related those findings to the proposed clinical criteria for CTE. METHODS: A sample of 166 community-dwelling men ages 40-60 was extracted from the normative database of the National Institutes of Health Toolbox. All participants denied prior head injury or traumatic brain injury (TBI). Participants completed scales assessing anger, hostility, aggression, anxiety, and depression. RESULTS: In response to the item "I felt angry," 21.1% of men reported "sometimes," and 4.8% reported "often." When asked "If I am provoked enough I may hit another person," 11.4% endorsed the statement as true. There were moderate correlations between anger and anxiety (Spearman's ρ=0.61) and between depression and affective anger (ρ=0.51), hostility (ρ=0.56), and perceived hostility (ρ=0.35). Participants were dichotomized into a possible depression group (N=49) and a no-depression group (N=117) on the basis of the question "I feel depressed," specific to the past 7 days. The possible depression group reported higher anxiety (p<0.001, Cohen's d=1.51), anger (p<0.001, Cohen's d=0.96), and hostility (p<0.001, Cohen's d=0.95). CONCLUSIONS: Some degree of anger and aggression are reported by a sizable minority of middle-aged men in the general population with no known history of TBI. Anger and hostility are correlated with depression and anxiety, indicating that all tend to co-occur. The base rates and comorbidity of affective dysregulation in men in the general population is important to consider when conceptualizing CTE phenotypes.

International study of video review of concussion in professional sports.

BACKGROUND: Video review has become an important tool in professional sporting codes to help sideline identification and management of players with a potential concussion. AIM: To assess current practices related to video review of concussion in professional sports internationally, and compare protocols and diagnostic criteria used to identify and manage potential concussions. METHODS: Current concussion management guidelines from professional national and international sporting codes were reviewed. Specific criteria and definitions of video signs associated with concussion were compared between codes. Rules and regulations adopted across the codes for processes around video review were also assessed. RESULTS: Six sports with specific diagnostic criteria and definitions for signs of concussion identified on video review participated in this study (Australian football, American football, world rugby, cricket, rugby league and ice hockey). Video signs common to all sports include lying motionless/loss of responsiveness and motor incoordination. The video signs considered by the majority of sports as most predictive of a diagnosis of concussion include motor incoordination, impact seizure, tonic posturing and lying motionless. Regulatory requirements, sideline availability of video, medical expertise of video reviewers and use of spotters differ across sports and geographical boundaries. By and large, these differences reflect a pragmatic approach from each sport, with limited underlying research and development of the video review process in some instances. CONCLUSIONS: The use of video analysis in assisting medical staff with the diagnosis or identification of potential concussion is well established across different sports internationally. The diagnostic criteria used and the expertise of the video review personnel are not clearly established, and research efforts would benefit from a collaborative harmonisation across sporting codes.

International consensus definitions of video signs of concussion in professional sports.

BACKGROUND: The use of video to assist professional sporting bodies with the diagnosis of sport-related concussion (SRC) has been well established; however, there has been little consistency across sporting codes with regards to which video signs should be used, and the definitions of each of these signs. AIM: The aims of this study were to develop a consensus for the video signs considered to be most useful in the identification of a possible SRC and to develop a consensus definition for each of these video signs across the sporting codes. METHODS: A brief questionnaire was used to assess which video signs were considered to be most useful in the identification of a possible concussion. Consensus was defined as >90% agreement by respondents. Existing definitions of these video signs from individual sports were collated, and individual components of the definitions were assessed and ranked. A modified Delphi approach was then used to create a consensus definition for each of the video signs. RESULTS: Respondents representing seven sporting bodies (Australian Football League, Cricket Australia, Major League Baseball, NFL, NHL, National Rugby League, World Rugby) reached consensus on eight video signs of concussion. Thirteen representatives from the seven professional sports ranked the definition components. Consolidation and refinement of the video signs and their definitions resulted in consensus definitions for six video signs of possible concussion: lying motionless, motor incoordination, impact seizure, tonic posturing, no protective action-floppy and blank/vacant look. CONCLUSIONS: These video signs and definitions have reached international consensus, are indicated for use by professional sporting bodies and will form the basis for further collaborative research.

White matter alterations over the course of two consecutive high-school football seasons and the effect of a jugular compression collar: A preliminary longitudinal diffusion tensor imaging study.

The cumulative effects of repetitive subclinical head impacts during sports may result in chronic white matter (WM) changes and possibly, neurodegenerative sequelae. In this pilot study, we investigated the longitudinal WM changes over the course of two consecutive high-school football seasons and explored the long-term effects of a jugular vein compression collar on these WM alterations. Diffusion tensor imaging data were prospectively collected both pre- and postseason in the two consecutive seasons. Participants were assigned into either collar or noncollar groups. Tract-based spatial statistics (TBSS) approach and region of interest-based approach were used to quantify changes in WM diffusion properties. Despite comparable exposure to repetitive head impacts, significant reductions in mean, axial, and/or radial diffusivity were identified in Season 1 in multiple WM regions in the noncollar group but not in the collar group. After an 8- to 9-month long off-season, these changes observed in the noncollar group partially and significantly reversed but also remained significantly different from the baseline. In Season 2, trend level WM alterations in the noncollar group were found but located in spatially different regions than Season 1. Last, the WM integrity in the collar group remained unchanged throughout the four time points. In conclusion, we quantitatively assessed the WM structural changes and partial reversal over the course of two consecutive high-school football seasons. In addition, the mitigated WM alterations in athletes in the collar group might indicate potential effect of the collar in ameliorating the changes against repetitive head impacts. Hum Brain Mapp 39:491-508, 2018. © 2017 Wiley Periodicals, Inc.

The Berlin 2016 process: a summary of methodology for the 5th International Consensus Conference on Concussion in Sport.

The purpose of this paper is to summarise the methodology for the 5th International Consensus Conference on Concussion in Sport. The 18 months of preparation included engagement of a scientific committee, an expert panel of 33 individuals in the field of concussion and a modified Delphi technique to determine the primary questions to be answered. The methodology also involved the writing of 12 systematic reviews to inform the consensus conference and submission and review of scientific abstracts. The meeting itself followed a 2-day open format, a 1-day closed expert panel meeting and two additional half day meetings to develop the Concussion Recognition Tool 5 (Pocket CRT5), Sport Concussion Assessment Tool 5 (SCAT5) and Child SCAT5.

What is the definition of sports-related concussion: a systematic review.

OBJECTIVES: Various definitions for concussion have been proposed, each having its strengths and weaknesses. We reviewed and compared current definitions and identified criteria necessary for an operational definition of sports-related concussion (SRC) in preparation of the 5th Concussion Consensus Conference (Berlin, Germany). We also assessed the role of biomechanical studies in informing an operational definition of SRC. DESIGN: This is a systematic literature review. DATA SOURCES: Data sources include MEDLINE, Embase, Cumulative Index to Nursing and Allied Health Literature, Cochrane Central Register of Clinical Trials and SPORT Discus (accessed 14 September 2016). ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Eligibility criteria were studies reporting (clinical) criteria for diagnosing SRC and studies containing SRC impact data. RESULTS: Out of 1601 articles screened, 36 studies were included (2.2%), 14 reported on criteria for SRC definitions and 22 on biomechanical aspects of concussions. Six different operational definitions focusing on clinical findings and their dynamics were identified. Biomechanical studies were obtained almost exclusively on American football players. Angular and linear head accelerations linked to clinically confirmed concussions demonstrated considerable individual variation. SUMMARY/CONCLUSIONS: SRC is a traumatic brain injury that is defined as a complex pathophysiological process affecting the brain, induced by biomechanical forces with several common features that help define its nature. Limitations identified include that the current criteria for diagnosing SRC are clinically oriented and that there is no gold/standard to assess their diagnostic properties. A future, more valid definition of SRC would better identify concussed players by demonstrating high predictive positive/negative values. Currently, the use of helmet-based systems to study the biomechanics of SRC is limited to few collision sports. New approaches need to be developed to provide objective markers for SRC.

A systematic review of potential long-term effects of sport-related concussion.

OBJECTIVE: Systematic review of possible long-term effects of sports-related concussion in retired athletes. DATA SOURCES: Ten electronic databases. STUDY SELECTION: Original research; incidence, risk factors or causation related to long-term mental health or neurological problems; individuals who have suffered a concussion; retired athletes as the subjects and possible long-term sequelae defined as >10 years after the injury. DATA EXTRACTION: Study population, exposure/outcome measures, clinical data, neurological examination findings, cognitive assessment, neuroimaging findings and neuropathology results. Risk of bias and level of evidence were evaluated by two authors. RESULTS: Following review of 3819 studies, 47 met inclusion criteria. Some former athletes have depression and cognitive deficits later in life, and there is an association between these deficits and multiple prior concussions. Former athletes are not at increased risk for death by suicide (two studies). Former high school American football players do not appear to be at increased risk for later life neurodegenerative diseases (two studies). Some retired professional American football players may be at increased risk for diminishment in cognitive functioning or mild cognitive impairment (several studies), and neurodegenerative diseases (one study). Neuroimaging studies show modest evidence of macrostructural, microstructural, functional and neurochemical changes in some athletes. CONCLUSION: Multiple concussions appear to be a risk factor for cognitive impairment and mental health problems in some individuals. More research is needed to better understand the prevalence of chronic traumatic encephalopathy and other neurological conditions and diseases, and the extent to which they are related to concussions and/or repetitive neurotrauma sustained in sports.

The Child Sport Concussion Assessment Tool 5th Edition (Child SCAT5): Background and rationale.

This article presents the Child Sport Concussion Assessment Tool 5th Edition (Child SCAT5). The Sport Concussion Assessment Tool was introduced in 2004, following the 2nd International Conference on Concussion in Sport in Prague, Czech Republic. Following the 4th International Consensus Conference, held in Zurich, Switzerland, in 2012, the SCAT 3rd edition (Child SCAT3) was developed for children aged between 5 and12 years. Research to date was reviewed and synthesised for the 5th International Consensus Conference on Concussion in Sport in Berlin, Germany, leading to the current revision of the test, the Child SCAT5. This article describes the development of the Child SCAT5.

What tests and measures should be added to the SCAT3 and related tests to improve their reliability, sensitivity and/or specificity in sideline concussion diagnosis? A systematic review.

OBJECTIVES: Several iterations of the Sport Concussion Assessment Tool (SCAT) have been published over the past 16 years. Our goal was to systematically review the literature related to the SCAT and provide recommendations for improving the tool. To achieve this goal, five separate but related searches were conducted and presented herein. DESIGN: Systematic literature review. DATA SOURCES: Medline, Embase, PsycINFO, Cumulative Index of Nursing and Allied Health Literature (CINAHL), Cochrane Central Register of Controlled Trials, SPORTDiscus and PubMed. ELIGIBILITY CRITERIA: Original, empirical, peer-reviewed findings published in English and included sports-related concussion (SRC). Review papers, case studies, editorials and conference proceedings/abstracts were excluded. The age range for the ChildSCAT was 5-12 years and for the Adult SCAT was 13 years and above. RESULTS: Out of 2961 articles screened, a total of 96 articles were included across the five searches. Searches were not mutually exclusive. The final number of articles included in the qualitative synthesis for each search was 21 on Adult SCAT, 32 on ChildSCAT, 21 on sideline, 8 on video/observation and 14 on oculomotor. SUMMARY/CONCLUSIONS: The SCAT is the most widely accepted and deployable sport concussion assessment and screening tool currently available. There is some degree of support for using the SCAT2/SCAT3 and ChildSCAT3 in the evaluation of SRC, with and without baseline data. The addition of an oculomotor examination seems indicated, although the most valid method for assessing oculomotor function is not clear. Video-observable signs of concussion show promise, but there is insufficient evidence to warrant widespread use at this time.

The Concussion Recognition Tool 5th Edition (CRT5): Background and rationale.

The Concussion Recognition Tool 5 (CRT5) is the most recent revision of the Pocket Sport Concussion Assessment Tool 2 that was initially introduced by the Concussion in Sport Group in 2005. The CRT5 is designed to assist non-medically trained individuals to recognise the signs and symptoms of possible sport-related concussion and provides guidance for removing an athlete from play/sport and to seek medical attention. This paper presents the development of the CRT5 and highlights the differences between the CRT5 and prior versions of the instrument.

The Sport Concussion Assessment Tool 5th Edition (SCAT5): Background and rationale.

This paper presents the Sport Concussion Assessment Tool 5th Edition (SCAT5), which is the most recent revision of a sport concussion evaluation tool for use by healthcare professionals in the acute evaluation of suspected concussion. The revision of the SCAT3 (first published in 2013) culminated in the SCAT5. The revision was based on a systematic review and synthesis of current research, public input and expert panel review as part of the 5th International Consensus Conference on Concussion in Sport held in Berlin in 2016. The SCAT5 is intended for use in those who are 13 years of age or older. The Child SCAT5 is a tool for those aged 5-12 years, which is discussed elsewhere.

Day-to-day variability of post-concussion-like symptoms reported over time by a non-concussed cohort.

PRIMARY OBJECTIVE: To explore the change (trend) in post-concussion-like symptoms reported over time. RESEARCH DESIGN: Longitudinal study. METHODS AND PROCEDURES: University students aged 18-30 years self-reported their symptoms experienced on a daily basis. Each participant was contacted via a text message each day during one of three pre-defined time zones to complete the Sport Concussion Assessment Tool 2 (SCAT2) post-concussion symptom scale on 7 consecutive days. MAIN OUTCOMES AND RESULTS: One hundred and ten (26 males and 84 females) students completed the study on all 7 days. Only two meaningful clusters emerged and comprised of a total of 105 participants. The primary cluster included 85 participants who showed a relatively stable pattern in their symptoms reported over time. Meanwhile, a second cluster comprised of 20 participants who demonstrated a decreasing trend in the reported symptom scores. CONCLUSIONS: The data indicated that non-concussed participants exhibited considerable individual variability in the symptom scores reported over time. However, some participants showed a systematic decreasing trend in their symptom scores reported over the 7 days. Caution must be exercised in interpreting the serial symptom scores that are obtained following a concussion, given that this study was conducted in a non-concussed cohort.

Cognitive and physical symptoms of concussive injury in children: a detailed longitudinal recovery study.

BACKGROUND: Recovery from concussion sustained in childhood and adolescence is poorly understood. We explored patterns of recovery for neurocognition and postconcussive symptoms following concussion in children and adolescents. METHODS: Using a prospective, longitudinal design, we collected baseline data on 728 children and adolescents aged 10-17 years. 10 participants sustained a concussive injury (n=10) in the 12 months following baseline testing and they were reviewed at day 5, 10 and 30 postconcussion. Assessments included the CogSport for Kids computerised test battery to evaluate neurocognitive function and self-report, and parent measures of postconcussive symptoms. At day 30, parents also completed measures rating their child's quality of life and executive functions. RESULTS: Children and adolescents displayed a gradual reduction in postconcussive symptoms over the 30 days following injury. At day 5, 87% of participants were reporting physical and cognitive symptoms, with a generalised reduction in all symptoms by day 10 (40% of participants). On the computerised measure, reaction time was slower after concussion, but returned to baseline levels by day 30. At day 30, 10% of participants demonstrated ongoing postconcussive symptoms. Number of previous concussions was related to speed of symptom resolution. CONCLUSIONS: At 5 days postconcussion, the majority of children and adolescents experienced debilitating postconcussive symptoms. However, by 30 days postinjury, 90% demonstrated recovery to normal for both neurocognition and postconcussive symptoms.

Does sports participation (including level of performance and previous injury) increase risk of osteoarthritis? A systematic review and meta-analysis.

BACKGROUND: To assess the relationship between sport and osteoarthritis (OA), and specifically to determine whether previous participation, in terms of level (elite or non-elite), type of sport, intensity or previous injury, was associated with OA. METHODS: This systematic review was developed using PRISMA guidelines. Databases were searched (to May 2016). Narrative review and meta-analysis (with risk ratio (RR) and 95% CIs) approaches were undertaken where appropriate. Study quality was assessed using GRADE. RESULTS: 46 studies were included. Narratively, 31 studies reported an increased risk of OA, with 19 demonstrating an increased risk in elite athletes. There was an increased risk after sports exposure (irrespective of type; RR 1.37; 95% CI 1.14 to 1.64; 21 studies). It remained uncertain whether there was a difference in risk of OA between elite and non-elite athletes (RR 1.37; 95% CI 0.84 to 2.22; 17 studies). The risk was higher in soccer (RR 1.42; 95% CI 1.14 to 1.77; 15 studies) but lower in runners (RR 0.86; 95% CI 0.53 to 1.41; 12 studies). 9 studies showed an association with the intensity of sport undertaken and OA. 5 studies demonstrated a higher prevalence of OA following meniscectomies and anterior cruciate ligament tears. Overall, the evidence was of GRADE 'very low' quality. CONCLUSIONS: There was very low-quality evidence to support an increased relationship between sports participation and OA in elite participants. It is unclear whether there is a difference in risk between elite and non-elite participants with further prospective studies needed to evaluate this. Pooled findings suggested that significant injuries were associated with OA in soccer players.

Smartphone and tablet apps for concussion road warriors (team clinicians): a systematic review for practical users.

BACKGROUND: Mobile technologies are steadily replacing traditional assessment approaches for the recognition and assessment of a sports concussion. Their ease of access, while facilitating the early identification of a concussion, also raises issues regarding the content of the applications (apps) and their suitability for different user groups. AIM: To locate and review apps that assist in the recognition and assessment of a sports concussion and to assess their content with respect to that of internationally accepted best-practice instruments. METHODS: A search of international app stores and of the web using key terms such as 'concussion', 'sports concussion' and variants was conducted. For those apps meeting the inclusion criteria, data were extracted on the platform, intended users and price. The content of each app was benchmarked to the Sport Concussion Assessment Tool 2 (SCAT2) and Pocket SCAT2 using a custom scoring scheme to generate a percentage compliance statistic. RESULTS: 18 of the 155 apps identified met the inclusion criteria. Almost all (16/18) were available on an iOS platform and only five required a payment to purchase. The apps were marketed for a wide range of intended users from medical professionals to the general public. The content of the apps varied from 0% to 100% compliance with the selected standard, and 'symptom evaluation' components demonstrated the highest level of compliance. CONCLUSIONS: The surge in availability of apps in an unregulated market raises concerns as to the appropriateness of their content for different groups of end users. The consolidation of best-practice concussion instruments now provides a framework to inform the development of future apps.

Chronic traumatic encephalopathy in sport: a systematic review.

OBJECTIVE: To provide a critical review of chronic traumatic encephalopathy (CTE) by considering the range of clinical presentations, neuropathology and the strength of evidence for CTE as a distinct syndrome. DATA SOURCES: Seven electronic databases were searched using a combination of MeSH terms and key words to identify relevant articles. REVIEW METHODS: Specific inclusion and exclusion criteria were used to select studies for review. Data extracted where present included study population, exposure/outcome measures, clinical data, neurological examination findings, cognitive assessment, investigation results and neuropathology results. RESULTS: The data from 158 published case studies were reviewed. Critical differences between the older descriptions of CTE (the 'classic' syndrome) and the recent descriptions (the 'modern' syndrome) exist in the age of onset, natural history, clinical features, pathological findings and diagnostic criteria, which suggests that modern CTE is a different syndrome. The methodology of the current studies does not allow determination of aetiology or risk factors. CONCLUSIONS: The clinicopathological differences between the 'classic' CTE syndrome and the 'modern' syndrome suggest that the new syndrome needs a different nomenclature. Further research is required to clearly define the clinical phenotype of the modern CTE syndrome and establish the underlying aetiology. Future research needs to address these issues through large-scale, prospective clinicopathological studies.

Big hits on the small screen: an evaluation of concussion-related videos on YouTube.

BACKGROUND: YouTube is one of the largest social networking websites, allowing users to upload and view video content that provides entertainment and conveys many messages, including those related to health conditions, such as concussion. However, little is known about the content of videos relating to concussion. OBJECTIVE: To identify and classify the content of concussion-related videos available on YouTube. STUDY DESIGN: An observational study using content analysis. METHODS: YouTube's video database was systematically searched using 10 search terms selected from MeSH and Google Adwords. The 100 videos with the largest view counts were chosen from the identified videos. These videos and their accompanying text were analysed for purpose, source and description of content by a panel of assessors who classified them into data-driven thematic categories. RESULTS: 434 videos met the inclusion criteria and the 100 videos with the largest view counts were chosen. The most common categories of the videos were the depiction of a sporting injury (37%) and news reports (25%). News and media organisations were the predominant source (51%) of concussion-related videos on YouTube, with very few being uploaded by professional or academic organisations. The median number of views per video was 26 191. CONCLUSIONS: Although a wide range of concussion-related videos were identified, there is a need for healthcare and educational organisations to explore YouTube as a medium for the dissemination of quality-controlled information on sports concussion.