title: Comparison between cylindrical axis-reference and articular surface-reference femoral bone cut for total knee arthroplasty.
abstract: OBJECTIVE
  Reproducing a functional flexion-extension axis (FEA) of the femur is key to achieving successful collateral ligament balance and joint line in total knee arthroplasty (TKA). This study compared the feasibility of cylindrical axis (CA)-reference bone cut and articular surface-reference bone cuts in reproducing the FEA for Japanese osteoarthritis patients.
  
  
  METHODS
  The study enrolled 122 knees from 86 patients who underwent primary TKA due to grade III or IV osteoarthritis. Data from pre-operative CT were reconstructed into three-dimensional (3D) models using 3D-planning software. Cylindrical radii of the condyles were measured, and femoral bone cut angles relative to anatomical landmarks were determined in the coronal and axial reference planes based on CA-reference and articular surface-reference methods.
  
  
  RESULTS
  Mean cylindrical radii for medial and lateral femoral condyles were 17.4 ± 1.6 and 17.3 ± 1.4 mm, respectively. Of the 122 knees, 46 exhibited >1 mm of difference between condyles. Fifty-three and 22 knees exhibited >2° of angular difference between CA-reference and articular surface-reference bone cuts in the coronal and axial planes. Mean angle of the CA and surgical epicondylar axis in 3D space was 4.6 ± 2.1°. As practical parameters for TKA, the angle between CA and IM rod was significantly larger than that between the distal articular surface line and IM rod in the coronal plane (p < 0.0001), indicating that CA-reference involves a smaller valgus bone cut of the distal femur than articular surface reference.
  
  
  CONCLUSIONS
  CA-reference bone cut of the femur is preferable to articular surface-reference bone cut for reproducing FEA in Japanese OA patients, in whom more than one-third of knees exhibited asymmetry of radii between medial and lateral condyles. In clinical practice, the CA-reference bone cut represents a good technical option for kinematically aligned TKA in the Japanese population.
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan. y-niki@keio.jp.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Niki
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Nagai
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Sassa
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Kengo
authors.initials: K
authors.lastname: Harato
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Suda
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D017885:Collateral Ligaments / Q000601:surgery; D005269:Femur / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*
keywords: Cylindrical axis; Cylindrical radius; Femoral condyle; Flexion–extension axis; Kinematically aligned total knee arthroplasty; Pre-operative planning