title: Decreased quadriceps activation measured hours prior to a noncontact anterior cruciate ligament tear.
abstract: METHODS
  Case report.
  
  
  BACKGROUND
  Decreased quadriceps activation has been shown to be present following anterior cruciate ligament (ACL) injury, but its presence prior to ACL injury is unknown. The purpose of this case report was to describe the level of quadriceps activation measured hours before a noncontact ACL injury in an individual who previously demonstrated known biomechanical risk factors for ACL injury.
  
  
  METHODS
  A 23-year-old female (height, 176.9 cm; mass, 72.4 kg), sustained a left noncontact ACL injury while landing from a jump stop during a recreational basketball game. This case was unique because data regarding landing biomechanics and quadriceps force and activation were gathered in 2 separate, unrelated studies prior to injury.
  
  
  RESULTS
  Peak external knee abduction moment (-65.3 Nm) during a drop jump landing 8 months prior to injury indicated elevated risk for ACL injury. Involved quadriceps central activation ratios (CAR) were obtained 1 week (CAR, 0.81) and 4 hours (CAR, 0.77) prior to injury. Strength and CAR (0.76) measurements changed very little within 36 hours of injury and both strength, and activation (CAR, 0.90) improved following surgical reconstruction and formal rehabilitation.
  
  
  CONCLUSIONS
  An individual with known biomechanical risk factors for ACL injury may compound risk for noncontact ACL injury if decreased quadriceps activation is also present.
  
  
  METHODS
  Prognosis, level 4.
authors.affiliation: University of Virginia, Charlottesville, VA 22903, USA. TGindstaff@virginia.edu
authors.forename: Terry L
authors.initials: TL
authors.lastname: Grindstaff
authors.forename: Kate R
authors.initials: KR
authors.lastname: Jackson
authors.forename: J Craig
authors.initials: JC
authors.lastname: Garrison
authors.forename: David R
authors.initials: DR
authors.lastname: Diduch
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Ingersoll
mesh_terms: D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D005260:Female; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007718:Knee Injuries / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D012421:Rupture; D013848:Thigh / Q000503:physiopathology; D055815:Young Adult