Defi nition and Classifi cation of Concussion

Traumatic brain injury (TBI) is a leading cause of hospitalization and death among children and adolescents and therefore represents a major public health problem (Langlois et al. 2006 ) . Recent estimates of pediatric TBI suggest an annual incidence of 475,000 cases for children ages 0 to 14 (Langlois et al. 2006 ) . However, most studies of TBI prevalence (i.e., all cases) and incidence (i.e., new cases) only include injuries associated with hospitalization resulting in fewer documented cases of milder forms of TBI such as concussions (Yeates 2010 ) . Two relatively recent population based studies in Canada have documented estimated prevalence rates for pediatric concussion at 200 per 100,000 (Gordon et al. 2006 ) and 135 per 100,000 (Willer et al. 2004 ) . However, these two studies are likely underestimates of the true prevalence of concussion, as the Gordon et al. ( 2006 ) study relied on retrospective report by parents of concussion that limited daily activity, and the Willer et al. ( 2004 ) study relied on narrative descriptions made by school staff not trained in recognizing the symptoms of concussion. Data from the US Centers for Disease Control and Prevention (CDC, Langlois et al. 2006 ) suggest that the prevalence rate for mild TBI in children is higher than these two studies when based on emergency department visits.