title: Cross-talk correction method for knee kinematics in gait analysis using principal component analysis (PCA): a new proposal.
abstract: BACKGROUND
  In 3D gait analysis, the knee joint is usually described by the Eulerian way. It consists in breaking down the motion between the articulating bones of the knee into three rotations around three axes: flexion/extension, abduction/adduction and internal/external rotation. However, the definition of these axes is prone to error, such as the "cross-talk" effect, due to difficult positioning of anatomical landmarks. This paper proposes a correction method, principal component analysis (PCA), based on an objective kinematic criterion for standardization, in order to improve knee joint kinematic analysis.
  
  
  METHODS
  The method was applied to the 3D gait data of two different groups (twenty healthy subjects and four with knee osteoarthritis). Then, this method was evaluated with respect to three main criteria: (1) the deletion of knee joint angle cross-talk (2) the reduction of variance in the varus/valgus kinematic profile (3) the posture trial varus/valgus deformation matching the X-ray value for patients with knee osteoarthritis. The effect of the correction method was tested statistically on variabilities and cross-talk during gait.
  
  
  RESULTS
  Cross-talk was lower (p<0.05) after correction (the correlation between the flexion-extension and varus-valgus kinematic profiles being annihilated). Additionally, the variance in the kinematic profile for knee varus/valgus and knee flexion/extension was found to be lower and higher (p<0.05), respectively, after correction for both the left and right side. Moreover, after correction, the posture trial varus/valgus angles were much closer to x-ray grading.
  
  
  CONCLUSIONS
  The results show that the PCA correction applied to the knee joint eliminates the cross-talk effect, and does not alter the radiological varus/valgus deformation for patients with knee osteoarthritis. These findings suggest that the proposed correction method produces new rotational axes that better fit true knee motion.
authors.affiliation: Centre d'Investigation Clinique INSERM 1432, Plateforme d'Investigation Technologique, Dijon University Hospital, Dijon, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Baudet
authors.affiliation: Centre d'Investigation Clinique INSERM 1432, Plateforme d'Investigation Technologique, Dijon University Hospital, Dijon, France; INSERM U1093, Dijon, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Morisset
authors.affiliation: Medical Information department, Dijon University Hospital, Dijon, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: d'Athis
authors.affiliation: INSERM U1093, Dijon, France; University of Burgundy, Dijon, France; Department of rheumatology, Dijon University Hospital, Dijon, France.
authors.forename: Jean-Francis
authors.initials: JF
authors.lastname: Maillefert
authors.affiliation: Centre d'Investigation Clinique INSERM 1432, Plateforme d'Investigation Technologique, Dijon University Hospital, Dijon, France; INSERM U1093, Dijon, France; University of Burgundy, Dijon, France; Department of physical medicine, Dijon University Hospital, Dijon, France.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Casillas
authors.affiliation: INSERM U1093, Dijon, France; University of Burgundy, Dijon, France; Department of rheumatology, Dijon University Hospital, Dijon, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Ornetti
authors.affiliation: Centre d'Investigation Clinique INSERM 1432, Plateforme d'Investigation Technologique, Dijon University Hospital, Dijon, France; INSERM U1093, Dijon, France.
authors.forename: Davy
authors.initials: D
authors.lastname: Laroche
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003627:Data Interpretation, Statistical; D005684:Gait; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology; D025341:Principal Component Analysis