title: Kinematics of anterior cruciate ligament ruptures in World Cup alpine skiing: 2 case reports of the slip-catch mechanism.
abstract: BACKGROUND
  Based on visual video analyses of 20 injury situations, the main mechanism of anterior cruciate ligament (ACL) injury in World Cup alpine skiing, termed the "slip-catch" mechanism, was identified. This situation is characterized by a common pattern in which the inside edge of the outer ski catches the snow surface while turning, forcing the knee into valgus and tibial internal rotation. To describe the exact joint kinematics at the time of injury, a more sophisticated approach is needed.
  
  
  OBJECTIVE
  To describe the knee and hip kinematics in 2 slip-catch situations utilizing a model-based image-matching (MBIM) technique.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Two typical slip-catch situations in World Cup alpine skiing reported through the International Ski Federation (FIS) Injury Surveillance System were captured on video with several camera views and high video quality. The injury situations were analyzed using the MBIM technique to produce continuous measurements of knee and hip joint kinematics.
  
  
  RESULTS
  Within 60 milliseconds, the knee flexion angle increased rapidly from 26° to 63° in case 1 and from 39° to 69° in case 2. In the same period, we observed a rapid increase in internal rotation of the tibia with a peak of 12° and 9°, respectively. The knee valgus angle changed less markedly in both cases. We also observed a rapid increase of hip flexion as well as substantial hip internal rotation.
  
  
  CONCLUSIONS
  Knee compression and knee internal rotation and abduction torque are important components of the injury mechanism in a slip-catch situation.
  
  
  CONCLUSIONS
  Prevention efforts should focus on avoiding a forceful tibial internal rotation in combination with knee valgus.
authors: Oslo Sports Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Pb 4014 Ullevaal Stadion, Oslo, N-0806, Norway. tone.bere@nih.no
authors: Tone
authors: T
authors: Bere
authors: Kam-Ming
authors: KM
authors: Mok
authors: Hideyuki
authors: H
authors: Koga
authors: Tron
authors: T
authors: Krosshaug
authors: Lars
authors: L
authors: Nordsletten
authors: Roald
authors: R
authors: Bahr
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D012399:Rotation; D012865:Skiing / Q000293:injuries*; D013977:Tibia / Q000503:physiopathology*; D019415:Torque; D014741:Video Recording
keywords: anterior cruciate ligament; injury biomechanics; injury mechanism; knee injury; professional alpine skiing; video analysis