title: Three distinct mechanisms predominate in non-contact anterior cruciate ligament injuries in male professional football players: a systematic video analysis of 39 cases.
abstract: BACKGROUND
  Current knowledge on anterior cruciate ligament (ACL) injury mechanisms in male football players is limited.
  
  
  OBJECTIVE
  To describe ACL injury mechanisms in male professional football players using systematic video analysis.
  
  
  METHODS
  We assessed videos from 39 complete ACL tears recorded via prospective professional football injury surveillance between 2001 and 2011. Five analysts independently reviewed all videos to estimate the time of initial foot contact with the ground and the time of ACL tear. We then analysed all videos according to a structured format describing the injury circumstances and lower limb joint biomechanics.
  
  
  RESULTS
  Twenty-five injuries were non-contact, eight indirect contact and six direct contact injuries. We identified three main categories of non-contact and indirect contact injury situations: (1) pressing (n=11), (2) re-gaining balance after kicking (n=5) and (3) landing after heading (n=5). The fourth main injury situation was direct contact with the injured leg or knee (n=6). Knee valgus was frequently seen in the main categories of non-contact and indirect contact playing situations (n=11), but a dynamic valgus collapse was infrequent (n=3). This was in contrast to the tackling-induced direct contact situations where a knee valgus collapse occurred in all cases (n=3).
  
  
  CONCLUSIONS
  Eighty-five per cent of the ACL injuries in male professional football players resulted from non-contact or indirect contact mechanisms. The most common playing situation leading to injury was pressing followed by kicking and heading. Knee valgus was frequently seen regardless of the playing situation, but a dynamic valgus collapse was rare.
authors.affiliation: Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden Football Research Group, Linköping, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Waldén
authors.affiliation: Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: Tron
authors.initials: T
authors.lastname: Krosshaug
authors.affiliation: Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: John
authors.initials: J
authors.lastname: Bjørneboe
authors.affiliation: Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: Thor Einar
authors.initials: TE
authors.lastname: Andersen
authors.affiliation: Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: Oliver
authors.initials: O
authors.lastname: Faul
authors.affiliation: Football Research Group, Linköping, Sweden Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-6883-1471
authors.initials: M
authors.lastname: Hägglund
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D001265:Athletic Injuries / Q000209:etiology / Q000503:physiopathology; D001696:Biomechanical Phenomena; D006801:Humans; D007718:Knee Injuries / Q000209:etiology / Q000503:physiopathology; D008297:Male; D012421:Rupture / Q000209:etiology; D012916:Soccer / Q000293:injuries*; D013548:Sweden; D014741:Video Recording
keywords: ACL; Anterior cruciate ligament; Football; Prevention; Soccer