**1. Introduction**

An estimated 41 million American children participate in competitive sports each year [1]. Participation in competitive sports is not without risk, however, as the Center for Disease Control reports that 2.7 million children aged 19 and under visited the emergency room annually for sports related injuries from 2001 to 2009 [2]. Specifically sports concussion is becoming an increasing public health issue as prevalence is estimated at 1.6–3.8 million annually [3]. Youth sports also contribute significantly to high rates of mild traumatic brain injury with 29% of sports related concussions happening in athletes between 16 and 19 years of age, and 40% of sports sports-related concussions occurring between 2001 and 2005 being sustained by children ages 8–13 [4, 5]. Although, cycling is the leading cause of head injury in children under the age of 14 [6], the three highest concussion rates in high school sports can be attributed to football, boys' ice hockey, and girls' soccer, with estimated rates of 76.8, 54, and 33 concussions per 100,000 athletic exposures, respectively [7]. These reports are likely underestimated as not all injured individuals seek medical care and therefore an estimated 50% of concussive injuries go unreported [8].

There is lack of a concrete and consistent definition of concussion which also creates challenges in the accuracy of sports related concussion epidemiology estimations. However, we share here the most widely accepted definition

of concussion most recently published by an international consensus group [9], which is defined as:

Concussion is a brain injury and is defined as a complex pathophysiological process affecting the brain, induced by biomechanical forces. Several common features that incorporate clinical, pathologic and biomechanical injury constructs that may be utilized in defining the nature of a concussive head injury include:


Concussions result in a myriad of symptomatology which are generally categorized into four main domains: (1) physical (i.e. headache, dizziness, visual dysfunction), (2) cognitive (i.e. difficult with concentration and memory), (3) emotional (i.e. depression, anxiety and mood lability), (4) sleep disturbance (hypersomnia and insomnia). The most commonly reported symptoms include headache, dizziness and difficulties with concentration and memory. Symptoms are likely caused by functional, metabolic and microstructural abnormalities as routine neuroimaging is typically unhelpful at demonstrating anatomical evidence of neuropathic changes [10].

Exposure to repetitive concussion or sub-concussive impacts, in which a significant traumatic brain injury may have occurred even in the absence of visible signs or symptoms, is now recognized as having possible long-term neurological consequences, including neurodegenerative disease [11–15]. Given the growing incidence and concern around sports concussion as well as the potential long-term sequelae associated with the injury, awareness of the current understanding of the pathophysiology is vital within the general field of sports medicine. Additionally, as targeted screening and management options are becoming increasingly available, knowledge of the current evidence-based tools for effective screening and subsequent management of the injury are important.
