title: Self-reported giving-way episode during a stepping-down task: case report of a subject with an ACL-deficient knee.
abstract: METHODS
  Case report.
  
  
  OBJECTIVE
  To describe the knee kinematics and moments of a giving-way trial of a subject with an anterior-cruciate-ligament- (ACL) deficient knee relative to his non-giving-way trials and to healthy subjects during a step-down task.
  
  
  BACKGROUND
  Episodes of giving way are believed to damage joint structures, therefore treatments aim to prevent giving-way episodes, yet few studies document giving-way events.
  
  
  METHODS
  The giving-way trial experienced by a 32-year-old male subject with ACL deficiency during a step-down task was compared to his non-giving-way trials (n = 5) and data from healthy subjects (n = 20). Position data collected at 60 Hz were combined with anthropometric data and ground reaction force data collected at 300 Hz to estimate knee displacement and 3-dimensional angles and net joint moments.
  
  
  RESULTS
  The knee joint displacement was higher during the giving-way trial: from 4% to 32% of stance, reaching 9.0 mm at 18% of stance as compared to 1.6 +/- 0.7 mm for the non-giving-way trials. After 4% of stance, the knee flexion angle of the giving-way trial was 6.6 degrees higher than the non-giving-way trials and was associated with a higher knee extension moment. The knee frontal plane moment was near neutral during early stance of the giving-way trial in contrast to the non-giving way and healthy subjects which demonstrated a knee abduction moment.
  
  
  CONCLUSIONS
  The response of this subject to the giving-way event suggests that higher knee flexion angles may enhance knee stability and, in reaction to the giving-way event, that knee extension moment may increase.
authors.affiliation: Ithaca College, Rochester Campus, Rochester, NY 14623, USA. jhouck@ithaca.edu
authors.forename: Jeff
authors.initials: J
authors.lastname: Houck
authors.forename: Amy
authors.initials: A
authors.lastname: Lerner
authors.forename: David
authors.initials: D
authors.lastname: Gushue
authors.forename: H John
authors.initials: HJ
authors.lastname: Yack
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology; D008124:Locomotion; D008297:Male; D012016:Reference Values; D012421:Rupture; D013647:Task Performance and Analysis