title: Relationship of the posterior femoral axis of the "kinematically aligned" total knee arthroplasty to the posterior condylar, transepicondylar, and anteroposterior femoral axes.
abstract: BACKGROUND
  A recent proposed modification in surgical technique in total knee arthroplasty (TKA) has been the introduction of the "kinematically aligned" TKA, in which the angle and level of the posterior joint line of the femoral component and joint line of the tibial component are aligned to those of the "normal," pre-arthritic knee. The purpose of this study was to establish the relationship of the posterior femoral axis of the "kinematically aligned" total knee arthroplasty (TKA) to the traditional axes used to set femoral component rotation.
  
  
  METHODS
  One hundred and fourteen consecutive, unselected patients with preoperative MRI images undergoing TKA were retrospectively reviewed. The transepicondylar axis (TEA), posterior condylar axis (PCA), antero-posterior axis (APA) of the trochlear groove, and posterior femoral axis of the kinematically aligned TKA (KAA) were templated on axial MRI images by two independent observers. The relationships between the KAA, TEA, APA, and PCA were determined, with a negative value indicating relative internal rotation of the axis.
  
  
  RESULTS
  On average, the KAA was 0.5° externally rotated relative to the PCA (minimum of -3.6°, maximum of 5.8°), -4.0° internally rotated relative to the TEA (minimum of -10.5°, maximum of 2.3°), and -96.4° internally rotated relative to the APA (minimum of -104.5°, maximum of -88.5°). Each of these relationships exhibited a wide range of potential values.
  
  
  CONCLUSIONS
  Using a kinematically aligned surgical technique internally rotates the posterior femoral axis relative to the transepicondylar axis, which significantly differs from current alignment instrument targets.
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Park
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Duncan
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Nunley
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Keeney
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Barrack
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, MO, USA. Electronic address: namd@wudosis.wustl.edu.
authors.forename: Denis
authors.initials: D
authors.lastname: Nam
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D005269:Femur / Q000473:pathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D012189:Retrospective Studies; D012399:Rotation; D013977:Tibia / Q000473:pathology
keywords: Femoral rotation; Flexion–extension axis; Kinematic alignment; Total knee arthroplasty; Transepicondylar axis
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