title: In vivo kinematics of a low contact stress rotating platform total knee arthroplasty system under weight bearing and non-weight bearing condition.
abstract: BACKGROUND
  The patterns and magnitudes of axial femorotibial rotation are variable due to the prosthesis design, ligamentous balancing, and surgical procedures. We aimed to investigate the effects of the weight bearing (WB) condition on the kinematics of mobile-bearing total knee arthroplasty (TKA).
  
  
  METHODS
  We examined 12 patients (19 knees) implanted with a low contact stress (LCS) mobile-bearing TKA system using a two-dimensional to three-dimensional registration technique. The in vivo kinematics of dynamic deep knee flexion under WB and non-WB (NWB) conditions were compared. We evaluated the knee range of motion, femoral axial rotation relative to the tibial component, anteroposterior translation, and kinematic pathway of the femorotibial contact point for both the medial and lateral sides.
  
  
  RESULTS
  Under the WB condition, the mean range of motion was 117.8° ± 16.7°. Under the NWB condition, the mean range of motion was 111.0° ± 4.4°. The mean range of axial rotation from full extension to maximum flexion was 3.0° ± 1.5° under the WB condition and 2.2° ± 1.0° under the NWB condition. With regard to the anteroposterior translation, the LCS mobile-bearing TKA system showed the same kinematic patterns under both conditions, except for axial rotation at 0°, 10°, and 110°. From hyperextension to maximum flexion, the kinematic pattern reflected a central pivot under both conditions.
  
  
  CONCLUSIONS
  In conclusion, this study demonstrated that, in an LCS mobile-bearing TKA system, knee kinematics showed the same patterns under NWB and WB conditions, except for axial rotation at the early phase. Further understanding of knee kinematics could provide us with useful information for future design concepts of TKA implants.
authors.affiliation: Department of Orthopaedic Surgery, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu, 501-1194, Japan, mkazuu@gifu-u.ac.jp.
authors.forename: Kazu
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Keishi
authors.initials: K
authors.lastname: Iwamoto
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Mori
authors.forename: Takaharu
authors.initials: T
authors.lastname: Yamasaki
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ito
authors.forename: Iori
authors.initials: I
authors.lastname: Takigami
authors.forename: Nobuo
authors.initials: N
authors.lastname: Terabayashi
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ogawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Tomita
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Akiyama
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology* / Q000601:surgery*; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D016896:Treatment Outcome; D016474:Weight-Bearing / Q000502:physiology