title: Mechanisms of ACL injury in professional rugby union: a systematic video analysis of 36 cases.
abstract: BACKGROUND
  The mechanisms of ACL injury in rugby are not well defined.
  
  
  OBJECTIVE
  To describe the mechanisms of ACL injury in male professional rugby players using systematic video analysis.
  
  
  METHODS
  36 cases from games played in top professional leagues and international matches were analysed. 5 analysts independently assessed all videos to record the estimated frame/time of initial ground contact, frame/time of ACL tear and a range of play specific variables. This included contact versus non-contact ACL injuries, injury timing, joint flexion angles and foot contact with the ground. 37 side-stepping manoeuvres from a control game were analysed to allow comparison of non-injury versus injury situations.
  
  
  RESULTS
  57% of ACL injuries occurred in a contact manner. 2 main scenarios were identified: (1) offensive running and (2) being tackled, indicating that the ball carrier might be at higher risk of ACL injury. The majority of non-contact ACL injuries resulted from a side-stepping manoeuvre. In most non-contact cases, initial ground contact was through heel strike. Statistical assessment of heel strike at initial ground contact versus non-heel strike cases showed a significant difference in injury versus non-injury outcomes, with heel strike associated with higher injury risk. Non-contact ACL injuries had lower median knee flexion angles and a more dorsiflexed ankle when compared with a control group (10° vs 20°, p≤0.001 and 10° vs 0°, p=0.033 respectively).
  
  
  CONCLUSIONS
  Over half of ACL injuries in rugby in our analysis resulted from a contact mechanism. For non-contact injuries, lower knee flexion angles and heel-first ground contact in a side-stepping manoeuvre were associated with ACL injury.
authors.affiliation: Department of Orthopaedics and Sports Medicine, School of Medicine, Trinity College Dublin, Ireland.|Sports Surgery Clinic, Santry, Dublin, Ireland.
authors.forename: Connor
authors.initials: C
authors.lastname: Montgomery
authors.affiliation: Centre for Bioengineering, School of Engineering, Trinity College Dublin, Dublin, Ireland.
authors.forename: Jeff
authors.initials: J
authors.lastname: Blackburn
authors.affiliation: Department of Orthopaedics and Sports Medicine, School of Medicine, Trinity College Dublin, Ireland.|Sports Surgery Clinic, Santry, Dublin, Ireland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Withers
authors.affiliation: Centre for Bioengineering, School of Engineering, Trinity College Dublin, Dublin, Ireland.
authors.forename: Gregory
authors.identifier: http://orcid.org/0000-0002-4666-4473
authors.initials: G
authors.lastname: Tierney
authors.affiliation: Department of Orthopaedics and Sports Medicine, School of Medicine, Trinity College Dublin, Ireland.|Sports Surgery Clinic, Santry, Dublin, Ireland.
authors.forename: Cathal
authors.initials: C
authors.lastname: Moran
authors.affiliation: Centre for Bioengineering, School of Engineering, Trinity College Dublin, Dublin, Ireland.
authors.forename: Ciaran
authors.initials: C
authors.lastname: Simms
mesh_terms: D000070598:Anterior Cruciate Ligament Injuries / Q000209:etiology*; D001265:Athletic Injuries / Q000209:etiology*; D001696:Biomechanical Phenomena; D005538:Football / Q000293:injuries*; D006365:Heel / Q000503:physiopathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D016059:Range of Motion, Articular; D012420:Running; D014741:Video Recording
keywords: ACL; Anterior cruciate ligament; Contact sports; Knee injuries; Rugby