Reference/Citation: Koh JO, Cassidy JD, Watkinson EJ. Incidence of concussion in contact sports: a systematic review of the evidence. Brain Inj. 2003;17:901–917..
Clinical Question: What is the incidence of concussion in various contact sports?
Data Sources: Studies for the review were found through a MEDLINE search (1985–2000) and by gathering and reviewing older articles referenced in the searched articles. The main terms that were included in the search were brain injuries, brain concussion, and incidence. Text words that were also included were mild traumatic brain injury, concussion, incidence, injury, and head injury, along with the names of 8 contact sports ( American football, boxing, ice hockey, judo, karate, tae kwon do, rugby, and soccer).
Study Selection: For this review, concussion was defined as “a mild brain injury resulting from a direct blow to the head resulting in physiological changes in brain function.” Cohort studies with documented incidence of concussion in athletes from 8 identified contact sports were the target of the search. All studies of male and female athletes in any of the 8 contact sports, including practices and games and regardless of level of competition, were included in the study search. Possible articles for review were identified through a 3-step screening process. Article titles were initially screened by one of the authors. If the title seemed to be relevant to the purpose of the review, the abstract of the article was then screened for inclusion/exclusion criteria as the second step. To be included, studies had to relate to the incidence of injury to the head and brain, report results relevant to concussion, involve 1 of the 8 identified contact sports, and be published between 1985 and 2000. All systematic reviews about mild traumatic brain injury (TBI) or concussion were also included. Studies were excluded if they discussed concussion due to whiplash injury or concussion associated with spinal cord injury, facial bone fracture, or soft tissue injuries; if they reported prevalence, rather than incidence, of concussion; if they addressed chronic TBI; if they comprised case reports or letters to the editor; or if they lacked a denominator to determine risk rates. Finally, relevant and unknown articles from the abstract screening were reviewed again for the inclusion and exclusion criteria by an independent, outside party.
Data Extraction: A general methodologic criteria design was used to critically appraise all articles that met the inclusion and exclusion criteria. This design appraised 11 study design and reporting criteria. In order for an article to be accepted into the systematic review, it had to meet at least the 5 mandatory criteria: description of the source population, appropriate description of inclusion and exclusion criteria, verifiable results from the raw data, differentiation of the incidence of injury between practice and game settings, and adequately measured denominator of population or person-time at risk. For each individual study, the 5 mandatory criteria listed above were rated with regard to whether they were included or addressed in the paper ( yes), were missing from the paper ( no), or were included but not described fully or in a way characterized by sound quality ( substandard). If any of the 5 mandatory criteria were rated no, the article was not evaluated any further. Data taken from these articles included sex, types of sessions in which concussion occurred, and numbers defining incidence of concussion within a contact sport. In some studies, rates were recalculated from the raw data in order to check accuracy, or if they were not presented in the published material, rates were calculated. These rates were recalculated with the denominator presented in the original study, athletes at risk for injury or time at risk for injury. Athlete-exposure was not defined in the review but is commonly used as the denominator in epidemiologic studies and represents one time in which an athlete takes part in a game or practice that exposes him or her to a risk for injury.
Main Results: The overall search identified 559 publications with possible relevance to the incidence of concussion in contact sports. After the titles were screened, 213 articles remained, and their abstracts were reviewed. The abstract screening for relevance yielded 127 articles to which the inclusion and exclusion criteria were applied. The investigators then critically reviewed 63 articles that fit the inclusion criteria. During this critical review, 40 articles did not meet the 5 mandatory criteria listed above and were not evaluated further. After final screening, 23 articles were included in the study. Review of these 23 articles revealed that among team sports for high school males, ice hockey athletes demonstrated the highest incidence of concussion (3.6 per 1000 athlete-exposures [AEs], 95% confidence interval [CI] = 0.99–9.29) and soccer athletes the lowest incidence of concussion (0.18 per 1000 AEs, 95% CI = 0.14–0.22). At the professional level, similar concussion incidence rates were found in both ice hockey (6.5 per 1000 player-games, 95% CI = 4.8–8.6) and rugby (9.05 per 1000 player-games, 95% CI = 4.1–17.1) players. When compared with other individual male sports (karate and tae kwon do), boxing had the highest incidence of concussion in professional (0.8 per 10 rounds, 95% CI = 0.75–0.95) and amateur (7.9 per 1000 man-minutes, 95% CI = 5.45–11.09) athletes. Only 6 included studies (5 dealing with tae kwon do and 1 with soccer) addressed concussion incidence in females. Tae kwon do had the highest incidence of concussion (8.77 per 1000 AEs, 95% CI = 0.22–47.9).
Conclusions: The information presented in the article offers helpful insight into the rate of concussion in athletes from 8 contact sports. Ice hockey seemed to have the greatest incidence of concussion for males, whereas tae kwon do had the highest incidence rate for females. Relatively few rigorous epidemiologic studies on the incidence of concussion exist. Specifically, 63% of the identified studies did not meet the methodologic criteria to be included in this systematic review. In addition, limited information exists on the risk of concussion for females in contact sports. Future authors should address the limitations in reporting incidences, including the lack of adequately measured denominators (person-time at risk), vague definitions of concussion, combining game and practice injuries, and history of concussive injury. Future researchers should also include at least the 5 mandatory methodologic criteria used in the critical appraisal of articles for this review to allow for better reporting of concussion incidence and comparison among various studies. Concussion incidence in females should also be explored.