Model for epidemiological studies on professional soccer player Arliani GG et al. studies. As a result, epidemiological studies in Brazil and other countries are characterized by a lack of uniformity in study design, data collection methods, injury definitions, standardized diagnostic criteria, and recovery time. To accurately interpret the results from epidemiological studies on professional soccer player injuries, findings from different studies must be compared. However, methodolo- gical differences in the various scientific studies have made meaningful comparisons impossible. Therefore, a uniform methodological model is needed to conduct epidemiological studies on professional soccer player injuries. This study aims to establish a methodological model for epidemiological studies on professional soccer player injuries and to describe the numerous previously published studies on this topic. Creating and establishing this model is very important because Brazil is quite different from European and other countries with respect to football and geography. MATERIALS AND METHODS This research project was approved by the Ethics Committee of Universidade Federal de Sa˜o Paulo/Escola Paulista de Medicina. To perform a meta-analysis of the existing studies on professional soccer player injuries, we developed an exten- sive search strategy using filters and a Boolean association strategy (MeSH term/Decs, Table 1). We included the Latin American and Caribbean Center on Health Sciences (LILACS, http://bases.bvs.br) and Medline databases (Table 1) in our study. For the Medline search, we used an initial filter limiting publications to those published after 2004 because there was a high-quality comprehensive review published that year.7 The search for articles in the LILACS database was performed from the onset of its creation (1982). Using the articles identified using the initial search strategy, two independent researchers manually identified all articles that could be included in this study. The inclusion criteria were as follows: epidemiological studies (cross-sectional, case-control, and cohort) and studies focused on non-recreational soccer players, including players under 17 years old, under 20 years old, and professionals. We excluded studies that focused exclusively on pediatric populations or included other sports in the analysis. In addition, we excluded studies that did not analyze muscu- loskeletal injuries. Studies by Ha¨gglund7 and Dro¨vak5 were used as the basis for this new model because they incorporated the relevant studies published prior to 2004. The titles and structured abstracts of studies were used to identify relevant articles. When the titles and abstracts provided insufficient information to determine inclusion or exclusion, the articles were read in full. When the two evaluators could not reach consensus regarding the inclusion of a particular article, a third evaluator assisted with the decision. Table 1 - Search Strategy. CLINICS 2011;66(10):1707-1712 A complete reading of all selected articles and the subsequent analysis of each study’s primary findings (Tables 2, 3) was performed to reach a consensus. To promote this consensus of the Brazilian Football Association (CBF), the researchers met during the preparation of the final document. RESULTS We considered 60 studies from Medline and 16 studies from LILACS in the final analysis. Twelve studies were selected for final inclusion in this review: seven from LILACS4-10 and five from Medline.11-15 The characteristics of each study are provided in Tables 2, 3, and 4. Prospective cohort studies were the most common studies (58%), followed by cross-sectional studies (25%) and retrospective studies (17%) (Tables 2, 3, and 4). DISCUSSION Epidemiological studies on professional soccer player injuries should be conducted prospectively based on a hierarchy of evidence. The prospective cohort design is more efficient than retrospective, cross-sectional, and case control studies. The retrospective study design, which was once widely used, has many biases that can reduce the validity of risk assessments. Therefore, the selection of a prospective design ensures that the measurement of injury risk is more reliable.16 To evaluate the risk of injury for a particular sport, one must consider the time of athlete’s exposure to sports activities, i.e., measure how long an individual athlete is exposed to the injury risk. The standard measure for reporting the incidence of soccer injuries is usually the number of injuries per 1000 hours of sports participation.17 Exposure assessments should be determined individually, as individual athletes will have different degrees of exposure due to varying training and playing time, even among players on the same team. Exposure time is the total number of hours of exposure for each individual, including the time spent training and the time played in games from the start of the monitoring period (usually the beginning of the season) until the first injury occurs or until the end of the monitoring period (if no injury occurs).7 Once a player recovers from an injury and resumes full participation in training and in games, the exposure time starts again. The study period must include at least one full season, including the preseason. Hagllund et al.11 demonstrated that the incidence of injuries was similar in two consecutive seasons, indicating that a study covering one full season can provide a sufficient overview of the incidence of injuries among elite soccer players. However, a prolonged study period is recommended for the analysis of specific patterns of injury. #1 ‘‘Athletic Injuries’’[Mesh] #2 Soccer"[Mesh] #3 random*[tiab] OR cohort*[tiab] OR risk*[tiab] OR causa*[tiab] OR predispose*[tiab] OR odds ratio[mh] OR case control* OR odds ratio* OR controlled clinical trial [pt] OR randomized controlled trial [pt] OR risk[mh] OR practice guideline[pt] OR epidemiologic studies[mh] OR case control studies[mh] OR cohort studies[mh] OR age factors[mh] OR comorbidity[mh] OR epidemiologic factors[mh] #4 #1 AND #2 AND #3 AND #4 Terms 1708