title: Knee separation distance and lower extremity kinematics during a drop land: implications for clinical screening.
abstract: BACKGROUND
  Excessive knee valgus during dynamic tasks is thought to contribute to lower extremity overuse and traumatic injuries. Clinically, assessments of frontal-plane knee motion typically include measures of the distance between the knees during landing. However, it is not clear how this clinical assessment relates to knee-abduction angle or how it is influenced by the position of the lower extremities in the transverse and frontal planes.
  
  
  OBJECTIVE
  To determine whether normalized knee separation distance (NKSD) is a predictor of knee-abduction angles and to assess the influence of lower extremity transverse-plane and frontal-plane angles on NKSD during a drop land.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Motion analysis laboratory.
  
  
  METHODS
  Twenty-five healthy female athletes.
  
  
  METHODS
  The frontal-plane distance between the 2-dimensional coordinates of markers over the greater trochanters (intertrochanteric distance), lateral femoral epicondyles (knee separation distance), and lateral malleoli (stance width) bilaterally was calculated during a drop land. The knee separation distance was normalized by intertrochanteric distance (NKSD). Concurrently, 3-dimensional lower extremity transverse-plane and frontal-plane kinematics were obtained.
  
  
  METHODS
  We assessed NKSD, stance width, and bilateral average knee and hip transverse plane and frontal-plane angles and ankle frontal-plane angles. Linear regression was used to determine the association between NKSD and bilateral average knee frontal-plane angles. Stepwise multiple regression was used to identify the best predictors of NKSD during the drop land.
  
  
  RESULTS
  After we controlled for stance width, NKSD explained 52% of the variance in the knee frontal-plane angle. When we took lower extremity kinematics into account, after controlling for stance width, the average hip frontal-plane angle was the best predictor of NKSD, explaining 97% of the variance.
  
  
  CONCLUSIONS
  Although NKSD is a predictor of knee-abduction angle, frontal-plane hip angle and stance width are strongly related to NKSD. Caution must be taken when interpreting NKSD as knee abduction.
authors.affiliation: Jacquelin Perry Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, CHP-155, University of Southern California, Los Angeles, CA 90089, USA. sigward@usc.edu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Sigward
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Havens
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Powers
mesh_terms: D000293:Adolescent; D000070598:Anterior Cruciate Ligament Injuries; D056352:Athletes; D001696:Biomechanical Phenomena; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008124:Locomotion; D035002:Lower Extremity / Q000502:physiology; D055815:Young Adult