title: Comparison of 2-dimensional measurement techniques for predicting knee angle and moment during a drop vertical jump.
abstract: OBJECTIVE
  To determine the association of 2-dimensional (2D) video-based techniques and 3-dimensional (3D) motion analysis to assess potential knee injury risk factors during jump landing.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Research laboratory.
  
  
  METHODS
  Thirty-six female athletes in cutting and pivoting sports.
  
  
  METHODS
  : Athletes performed a drop vertical jump during which movement was recorded with a motion analysis system and a digital video camera positioned in the frontal plane.
  
  
  METHODS
  The 2D variables were the frontal plane projection angle (FPPA), the angle formed between thigh and leg, and the knee-to-ankle separation ratio, the distance between knee joints divided by the distance between ankles. The 3D variables were knee abduction angle and external abduction moment. All variables were assessed at peak knee flexion. Linear regression assessed the relationship between the 2D and 3D variables. In addition, intraclass correlation coefficients (ICC) determined rater reliability for the 2D variables and compared the 2D measurements made from digital video with the same measurements from the motion analysis.
  
  
  RESULTS
  : The knee-to-ankle separation ratio accounted for a higher variance of 3D knee abduction angle (r = 0.350) and knee abduction moment (r = 0.394) when compared with the FPPA (r = 0.145, 0.254). The digital video measures had favorable rater reliability (ICC, 0.89-0.94) and were comparable with the motion analysis system (ICC, ≥ 0.92).
  
  
  CONCLUSIONS
  When compared with the FPPA, the knee-to-ankle separation ratio had better association with previously cited knee injury risk factors in female athletes. The 2D measures have adequate consistency and validity to merit further clinical consideration in jump landing assessments.
authors.affiliation: School of Physical Therapy & Rehabilitation Science, The University of Montana, Missoula, Montana 59812, USA. ryan.mizner@umontana.edu
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Mizner
authors.forename: Terese L
authors.initials: TL
authors.lastname: Chmielewski
authors.forename: John J
authors.initials: JJ
authors.lastname: Toepke
authors.forename: Kari B
authors.initials: KB
authors.lastname: Tofte
mesh_terms: D000293:Adolescent; D056352:Athletes; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007717:Knee / Q000502:physiology*; D007718:Knee Injuries / Q000503:physiopathology; D015203:Reproducibility of Results; D012307:Risk Factors; D014741:Video Recording; D055815:Young Adult