title: Misalignment of the knees: does it affect human stance stability.
abstract: BACKGROUND
  Data describing the relationships between postural alignment and stance stability are scarce and controversial.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the effects of sensory disturbances on knee alignment in upright stance and the effects of knee hyperextension on stance stability.
  
  
  METHODS
  Kinetic and kinematic data of 23 healthy adult women were collected while quietly standing in four sensory conditions. Kinematic data: knee angle (dependent variables) variations were analyzed across sensory conditions. Kinetic data: as subjects with hyperextended knees showed a clear tendency to flex their knees as balance challenge increased, center of pressure (COP) parameters (dependent variables) were analyzed in each sensory condition among trial sub-groups: Aligned-Trials (knee angle<180°), Hyperextended-Trials (>180°) and Adjusted-Trials (>180° initially, turned <180° under challenging conditions).
  
  
  RESULTS
  Differences were found in mean velocity of COP in two conditions showing that knee alignment can affect stance stability.
  
  
  CONCLUSIONS
  Knee hyperextension is a transient condition changing under postural challenges. Knee hyperextension affected postural control as mean velocity was the highest in the hyperextended group in natural standing sensory condition and lowest with sensory disturbance.
authors.affiliation: Department of Physical Therapy, Communication Science & Disorders and Occupational Therapy, Faculty of Medicine, University of São Paulo, São Paulo, Brazil. fisioterapia.ichc@hcnet.usp.br
authors.forename: Cássio Marinho
authors.initials: CM
authors.lastname: Siqueira
authors.forename: Gabriel Bueno
authors.initials: GB
authors.lastname: Lahoz Moya
authors.forename: Rene Rogieri
authors.initials: RR
authors.lastname: Caffaro
authors.forename: Carolina
authors.initials: C
authors.lastname: Fu
authors.forename: André Fábio
authors.initials: AF
authors.lastname: Kohn
authors.forename: César Ferreira
authors.initials: CF
authors.lastname: Amorim
authors.forename: Clarice
authors.initials: C
authors.lastname: Tanaka
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*