title: Mechanisms of anterior cruciate ligament injury in World Cup alpine skiing: a systematic video analysis of 20 cases.
abstract: BACKGROUND
  There is limited insight into the mechanisms of anterior cruciate ligament injuries in alpine skiing, particularly among professional ski racers.
  
  
  OBJECTIVE
  This study was undertaken to qualitatively describe the mechanisms of anterior cruciate ligament injury in World Cup alpine skiing.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  Twenty cases of anterior cruciate ligament injuries reported through the International Ski Federation Injury Surveillance System for 3 consecutive World Cup seasons (2006-2009) were obtained on video. Seven international experts in the field of skiing biomechanics and sports medicine related to alpine skiing performed visual analyses of each case to describe the injury mechanisms in detail (skiing situation, skier behavior, biomechanical characteristics).
  
  
  RESULTS
  Three main categories of injury mechanisms were identified: slip-catch, landing back-weighted, and dynamic snowplow. The slip-catch mechanism accounted for half of the cases (n = 10), and all these injuries occurred during turning, without or before falling. The skier lost pressure on the outer ski, and while extending the outer knee to regain grip, the inside edge of the outer ski caught abruptly in the snow, forcing the knee into internal rotation and valgus. The same loading pattern was observed for the dynamic snowplow (n = 3). The landing back-weighted category included cases (n = 4) where the skier was out of balance backward in flight after a jump and landed on the ski tails with nearly extended knees. The suggested loading mechanism was a combination of tibiofemoral compression, boot-induced anterior drawer, and quadriceps anterior drawer.
  
  
  CONCLUSIONS
  Based on this video analysis of 20 injury situations, the main mechanism of anterior cruciate ligament injury in World Cup alpine skiing appeared to be a slip-catch situation where the outer ski catches the inside edge, forcing the outer knee into internal rotation and valgus. A similar loading pattern was observed for the dynamic snowplow. Injury prevention efforts should focus on the slip-catch mechanism and the dynamic snowplow.
authors.affiliation: Oslo Sports Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway. tone.bere@nih.no
authors.forename: Tone
authors.initials: T
authors.lastname: Bere
authors.forename: Tonje Wåle
authors.initials: TW
authors.lastname: Flørenes
authors.forename: Tron
authors.initials: T
authors.lastname: Krosshaug
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Koga
authors.forename: Lars
authors.initials: L
authors.lastname: Nordsletten
authors.forename: Christopher
authors.initials: C
authors.lastname: Irving
authors.forename: Erich
authors.initials: E
authors.lastname: Muller
authors.forename: Robert Cortas
authors.initials: RC
authors.lastname: Reid
authors.forename: Veit
authors.initials: V
authors.lastname: Senner
authors.forename: Roald
authors.initials: R
authors.lastname: Bahr
mesh_terms: D000070598:Anterior Cruciate Ligament Injuries; D001265:Athletic Injuries / Q000209:etiology; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D012399:Rotation / Q000009:adverse effects; D012865:Skiing / Q000293:injuries*; D013314:Stress, Mechanical; D014741:Video Recording