title: The clinical epicondylar axis is not the functional flexion axis of the human knee.
abstract: BACKGROUND
  The functional flexion axis (FFA) is the principal axis around which the knee moves and thus, by definition, does not move in vertical displacement relative to the tibia. The transepicondylar axis (TEA) has been reported to coincide with the FFA. If that is not true, the TEA should show vertical displacement during motion, and this hypothesis was investigated.
  
  
  METHODS
  Three-dimensional knee kinematics of 20 healthy volunteers were determined during a squatting motion via a 3-dimensional to 2-dimensional image registration technique by calculating the vertical displacement of the clinical epicondylar axis (CEA) through the full range of motion.
  
  
  RESULTS
  From 0° to 90° knee flexion, the average vertical displacement of the lateral end of the CEA was <3 mm, whereas that of the medial end was large (7.6 mm).
  
  
  CONCLUSIONS
  The large vertical displacement of the medial end of the CEA suggests that the CEA is not the FFA. This finding implies that the CEA may not be an appropriate axis for a TKA prosthesis having a "single radius" design.
  
  
  METHODS
  Level IV.
authors: Department of Orthopaedic Surgery, Niigata Medical Center, Niigata, Japan, tomo07301977@yahoo.co.jp.
authors: Tomoharu
authors: T
authors: Mochizuki
authors: Takashi
authors: T
authors: Sato
authors: John David
authors: JD
authors: Blaha
authors: Osamu
authors: O
authors: Tanifuji
authors: Koichi
authors: K
authors: Kobayashi
authors: Hiroshi
authors: H
authors: Yamagiwa
authors: Satoshi
authors: S
authors: Watanabe
authors: Yoshio
authors: Y
authors: Koga
authors: Go
authors: G
authors: Omori
authors: Naoto
authors: N
authors: Endo
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D014057:Tomography, X-Ray Computed