title: Mechanisms of noncontact anterior cruciate ligament injury.
abstract: OBJECTIVE
  To examine and summarize previous retrospective and observational studies assessing noncontact anterior cruciate ligament (ACL) injury mechanisms and to examine such reported ACL injury mechanisms based on ACL loading patterns due to knee loadings reported in in vivo, in vitro, and computer simulation studies.
  
  
  METHODS
  We searched MEDLINE from 1950 through 2007 using the key words anterior cruciate ligament + injury + mechanisms; anterior cruciate ligament + injury + mechanisms + retrospective; and anterior cruciate ligament + injury + mechanisms + video analysis.
  
  
  METHODS
  We selected retrospective studies and observational studies that specifically examined the noncontact ACL injury mechanisms (n = 7) and assessed ACL loading patterns in vivo, in vitro, and using computer simulations (n = 33).
  
  
  METHODS
  The motion patterns reported as noncontact ACL injury mechanisms in retrospective and observational studies were assessed and critically compared with ACL loading patterns measured during applied external or internal (or both) forces or moments to the knee.
  
  
  RESULTS
  Noncontact ACL injuries are likely to happen during deceleration and acceleration motions with excessive quadriceps contraction and reduced hamstrings co-contraction at or near full knee extension. Higher ACL loading during the application of a quadriceps force when combined with a knee internal rotation moment compared with an external rotation moment was noted. The ACL loading was also higher when a valgus load was combined with internal rotation as compared with external rotation. However, because the combination of knee valgus and external rotation motions may lead to ACL impingement, these combined motions cannot be excluded from the noncontact ACL injury mechanisms. Further, excessive valgus knee loads applied during weight-bearing, decelerating activities also increased ACL loading.
  
  
  CONCLUSIONS
  The findings from this review lend support to ACL injury prevention programs designed to prevent unopposed excessive quadriceps force and frontal-plane or transverse-plane (or both) moments to the knee and to encourage increased knee flexion angle during sudden deceleration and acceleration tasks.
authors.affiliation: Osaka University of Health and Sport Sciences, Sennan-gun, Osaka, Japan. yshimoko@ouhs.ac.jp
authors.forename: Yohei
authors.initials: Y
authors.lastname: Shimokochi
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
mesh_terms: D000054:Acceleration; D016118:Anterior Cruciate Ligament / Q000503:physiopathology*; D000070598:Anterior Cruciate Ligament Injuries; D003198:Computer Simulation; D006801:Humans; D007718:Knee Injuries / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000293:injuries; D016059:Range of Motion, Articular; D012307:Risk Factors