title: Concussions in the National Football League: A Current Concepts Review.
abstract: BACKGROUND
  Significant attention has been directed toward the immediate and long-term effects of sport-related concussions on athletes participating in contact sports, particularly football. The highest level of football, the National Football League (NFL), has received significant attention and criticism regarding player management and safety after mild traumatic brain injury (mTBI). Several review articles have reported data related to concussion in the NFL, but a succinct review and synthesis of data regarding NFL concussions is currently lacking.
  
  
  OBJECTIVE
  To (1) review systematically the published data regarding concussion in the NFL and assess limitations of the studies, (2) elucidate areas where further research is needed, and (3) identify methods to improve future investigations of concussion in the NFL.
  
  
  METHODS
  Systematic review of literature.
  
  
  METHODS
  English-language titles and abstracts published between 1900 and September 2014 were searched systematically across electronic databases, and a review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Peer-reviewed journal articles were included if they contained NFL concussion data with or without additional associated long-term effects. Reviews, editorials, letters to the editor, and comments were not included.
  
  
  RESULTS
  Of the 344 records screened for review, 88 articles were assessed for eligibility. There were 31 studies that met the inclusion criteria and formed the basis of the evidence synthesis. Included in the current review were 8 case-control studies (Oxford Centre for Evidence-Based Medicine evidence level 3b), 6 descriptive epidemiological studies (level 4), 6 cross-sectional studies (level 4), 6 cohort studies (level 2b), and 5 case series (level 4).
  
  
  CONCLUSIONS
  The study of concussions in the NFL has been limited by lack of recent empirical data, reliance on self-reported concussion history, and ascertainment bias of brains donated for autopsy studies. The scientific community as well as the public should be cautious in interpreting the current literature surrounding concussion.
authors.affiliation: Vanderbilt Sports Concussion Center, Vanderbilt University School of Medicine, Nashville, Tennessee, USA aaron.m.yengo-kahn@vanderbilt.edu.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Yengo-Kahn
authors.affiliation: Vanderbilt Sports Concussion Center, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Johnson
authors.affiliation: Vanderbilt Sports Concussion Center, Vanderbilt University School of Medicine, Nashville, Tennessee, USA Department of Neurological Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Zuckerman
authors.affiliation: Vanderbilt Sports Concussion Center, Vanderbilt University School of Medicine, Nashville, Tennessee, USA Department of Neurological Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Solomon
mesh_terms: D001265:Athletic Injuries / Q000453:epidemiology* / Q000517:prevention & control; D001924:Brain Concussion / Q000453:epidemiology* / Q000517:prevention & control; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005538:Football / Q000293:injuries*; D006260:Head Protective Devices / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D035002:Lower Extremity / Q000293:injuries; D008297:Male; D009141:Musculoskeletal System / Q000293:injuries; D012307:Risk Factors; D014481:United States
keywords: NFL; chronic traumatic encephalopathy; concussion; neuropsychological testing