Aim or objective The aim of this study is to consolidate studies of physiological measures following sport-related concussion (SRC) to determine if a time course of postinjury altered neurobiology can be outlined. This biological time course was considered with respect to clinically relevant outcomes such as vulnerability to repeat injury and safe timing of return to physical contact risk.
Design Systematic review.
Data sources PubMed, CINAHL, Cochrane Central, PsychINFO.
Eligibility criteria for selecting studies Studies were included if they reported original research on physiological or neurobiological changes after SRC. Excluded were cases series <5 subjects, reviews, meta-analyses, editorials, animal research and research not pertaining to SRC.
Results A total of 5834 articles were identified, of which 80 were included for full-text data extraction and review. Relatively few longitudinal studies exist that follow both physiological dysfunction and clinical measures to recovery.
Summary/conclusions Modalities of measuring physiological change after SRC were categorised into the following: functional MRI, diffusion tensor imaging, magnetic resonance spectroscopy, cerebral blood flow, electrophysiology, heart rate, exercise, fluid biomarkers and transcranial magnetic stimulation. Due to differences in modalities, time course, study design and outcomes, it is not possible to define a single ‘physiological time window’ for SRC recovery. Multiple studies suggest physiological dysfunction may outlast current clinical measures of recovery, supporting a buffer zone of gradually increasing activity before full contact risk. Future studies need to use generalisable populations, longitudinal designs following to physiological and clinical recovery and careful correlation of neurobiological modalities with clinical measures.
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Acknowledgements We thank our UCLA Biomedical Librarian, Rikke Ogawa and her colleague Bethany Myers, who assisted with development of the search strategies and conducted the literature searches. We are also very grateful to Philip Rosenbaum for assisting with organisation of the project, managing the reference library and proofreading and Joshua Stanley for assisting in data extraction.
Competing interests JK—Fellowship partially supported by UCLA Steve Tisch BrainSPORT programme. EB—grants/research support: National Institute of Child Health and Human Development (grant Nos 5R01HD048946 and 3R01HD048946-05S1) and the USA. Army Medical Research and Material Command under Award No W81XWH-13-2-0095 (Chronic Effects of Neurotrauma Consortium); Director—Neuropsychological Research and Assessment Lab at BYU's Comprehensive Clinic. Medicolegal: Some forensic cases. TC—grants/research support: Brainscope, Datalys, Pentecost Foundation. SK—Chief Medical Officer, Rugby Football Union; Committee Member: World Rugby Head Injury Assessment Working Group and Football Association Independent Panel on Concussion and Head Injury. JJL—grants/research support: NIH, The Ralph C. Wilson Foundation, Program for Understanding Childhood Concussion and Stroke, The Robert Rich Family Foundation and The Buffalo Sabres Foundation. AM—grants/research support: NIH, US Dept of Defense, NSF. MMC—grants/research support: US Dept of Defense, US Dept of Veteran’s Affairs, NCAA, NFL-GE, GE Health Care, MCW CTSI, private donors; Consultant: Green Bay Packers; Past member: NFL Head, Neck and Spine Committee (w/o compensation); Member: GE Healthcare Medical Advisory Board, Board of Governors for International Neuropsychological Society. KJS—Consultant, Evidence Sport and Spinal Therapy; speaking honoraria for presentations at scientific meetings. TCVM—Trustee, United States Brain Injury Alliance; Senior Associate Editor: Journal of Athletic Training, Associate Editor: Journal of Sport Rehabilitation; Consultant, Concussion Health. RZ—grants/research support: CIHR, Ontario Neurotrauma Foundation, Ontario SPOR Support Unit, Clinical Research Chair in Pediatric Concussion, University of Ottawa Brain and Mind Institute. CCG—grants/research support: NIH, NCAA, US Department of Defense, Today’s and Tomorrow’s Children Fund, UCLA Brain Injury Research Center, UCLA Faculty Grants Program, UCLA Steve Tisch BrainSPORT programme, Avanir (research grant 2017-2018), NINDS Neural Analytics SBIR grant (2016-2018); Consultant: NFL—Neurological Care Program, NHLPA, Neural Analytics Inc (2015-16); Advisory Panel: LoveYourBrain, MLS, NBA, NCAA, USSF; Medicolegal: One or two cases annually; Speaker’s Bureau: Medical Education Speakers Network.
Provenance and peer review Not commissioned; externally peer reviewed.
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