title: Risk factors for acute knee injury in female youth football.
abstract: OBJECTIVE
  To prospectively evaluate risk factors for acute time-loss knee injury, in particular ACL injury, in female youth football players.
  
  
  METHODS
  Risk factors were studied in 4556 players aged 12-17 years from a randomised controlled trial during the 2009 season. Covariates were both intrinsic (body mass index, age, relative age effect, onset of menarche, previous acute knee injury or ACL injury, current knee complaints, and familial disposition of ACL injury) and extrinsic (no. of training sessions/week, no. of matches/week, match exposure ratio, match play with other teams, and artificial turf exposure). Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated from individual variable and multiple Cox regression analyses.
  
  
  RESULTS
  Ninety-six acute knee injuries were recorded, 21 of them ACL injuries. Multiple Cox regression showed a fourfold higher ACL injury rate for players with familial disposition of ACL injury (HR 3.57; 95% CI 1.48-8.62). Significant predictor variables for acute knee injury were age >14 years (HR 1.97; 95% CI 1.30-2.97), knee complaints at the start of the season (HR 1.98; 95% CI 1.30-3.02), and familial disposition of ACL injury (HR 1.96; 95% CI 1.22-3.16). No differences in injury rates were seen when playing on artificial turf compared with natural grass.
  
  
  CONCLUSIONS
  Female youth football players with a familial disposition of ACL injury had an increased risk of ACL injury and acute knee injury. Older players and those with knee complaints at pre-season were more at risk of acute knee injury. Although the predictive values were low, these factors could be used in athlete screening to target preventive interventions.
  
  
  METHODS
  II.
authors.affiliation: Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, 58183, Linköping, Sweden. martin.hagglund@liu.se.|Football Research Group, Linköping, Sweden. martin.hagglund@liu.se.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-6883-1471
authors.initials: M
authors.lastname: Hägglund
authors.affiliation: Football Research Group, Linköping, Sweden.|Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, 58183, Linköping, Sweden.|Department of Orthopaedics, Hässleholm-Kristianstad-Ystad Hospitals, Hässleholm, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Waldén
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007718:Knee Injuries / Q000453:epidemiology* / Q000209:etiology; D011446:Prospective Studies; D012307:Risk Factors; D012916:Soccer / Q000293:injuries*
keywords: ACL; Epidemiology; Female athlete; Knee; Prevention; Soccer