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.
Competing Interests: Competing interests: PM is a co-investigator, collaborator or consultant on grants relating to mild TBI funded by several governmental organisations. He is directly employed by the National Health and Medical Research Council of Australia and is based at the Florey Institute of Neuroscience and Mental Health. He is co-chair of the Australian Centre for Research into Sports Injury and its Prevention (ACRISP), which is one of the International University Research Centres for Prevention of Injury and Protection of Athlete Health supported by the International Olympic Committee (IOC). He is co-chair of the International Concussion in Sport Group. He has a clinical and consulting practice in general and sports neurology. He receives book royalties from McGraw-Hill and was employed in an editorial capacity by the British Medical Journal Publishing Group from 2001 to 2008. He has been reimbursed by the government, professional scientific bodies and sporting bodies for travel costs related to presenting research on mild TBI and sports-related concussion at meetings, scientific conferences and symposiums. He received consultancy fees in 2010 from Axon Sports (USA) for the development of educational material (which was not renewed) and has received research funding since 2001 from CogState Inc. He has not received any research funding, salary or other monies from the Australian Football League, FIFA or the National Football League. The Australian Football League funds research at the Florey Institute under a legal memorandum and PM does not receive any money from this industry-funded research. PM is a cofounder and shareholder in two biomedical companies (involved in eHealth and compression garment technologies) but does not hold any individual shares in any company related to concussion or brain injury assessment or technology. He did not receive any form of financial support directly related to this manuscript. NF-D and JD report no conflicts of interest. AM is a self-employed consultant and holds honorary academic appointments. He has been funded as a consultant to undertake research and policy related work for government, sports federations and industry on the topic of safety and injury risk management, including concussion, head injury and helmets. He did not receive any form of financial support directly related to this manuscript. He reports no conflicts of interest. PEV is a neurologist and Chairman of the Steering Commitee of a trial in traumatic brain injury sponsored by EVER Neuro Pharma GmbH. He has been funded as a consultant for EVER Neuro Pharma. He did not receive any form of financial support directly related to this manuscript. He reports no conflicts of interest. JDC is an injury epidemiologist employed by the University Health Network, University of Toronto. He is a professor in the Division of Epidemiology and the Institute of Health Policy, Management and Evaluation at the Dalla Lana School of Public Health, University of Toronto. He has received funding from the Ontario Neurotrauma Foundation to undertake systematic reviews on mild traumatic brain injury and served on the WHO Collaborating Centre Task Force on Mild Traumatic Brain Injury, which received funding from various sources, including traffic insurance companies in North America and Europe. He was retained as an expert witness for the National Hockey League on November 30, 2016. He did not receive any form of financial support related to this manuscript, and has no other conflicts of interest to report. RJE is a consultant to the National Hockey League, Major League Soccer, US Soccer Federation and Princeton University. He receives financial remuneration for these consulting relationships. He has a clinical practice in sport neuropsychology and serves as an expert (neuropsychology and sport neuropsychology) in medico-legal cases involving traumatic brain injury. WM is the Medical Director of the National Hockey League. He has received research grant support through the University of Calgary from the Canadian Institutes of Health Research, Alberta Innovates Health Solutions, the International Football Association (FIFA), Alberta Children’s Hospital Research Institute and the Hotchkiss Brain Institute. He is the founding Chair of the Sport Injury Prevention Research Centre, which is one of the International Research Centres for Prevention of Injury and Protection of Athlete Health supported by the International Olympic Committee (IOC). He has a clinical consulting practice in sport medicine at the University of Calgary Sport Medicine Centre. He is an Expert Group member of the IOC Medical Commission and has received travel funding in that capacity.
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