title: In vivo kinematics of mobile-bearing total knee arthroplasty during deep knee bending under weight-bearing conditions.
abstract: OBJECTIVE
  Little is known about the in vivo kinematics of mobile-bearing total knee arthroplasty, especially at deep knee flexion under weight-bearing conditions.
  
  
  METHODS
  In vivo knee kinematics was analyzed for 12 patients (13 knees) implanted with PFC-Sigma Rotating Platform-Flex (RP-F) prostheses. Under fluoroscopic surveillance, each patient performed weight-bearing deep knee bending. Motion between each component was analyzed using a two- to three-dimensional registration technique, which uses computer-assisted design models to reproduce the spatial positions of the femoral and tibial components and a polyethylene insert (implanted with four tantalum beads) from single-view fluoroscopic images.
  
  
  RESULTS
  External rotation of the femoral component on the tibial tray was mostly caused by rotation of the polyethylene insert on the tibial tray. The femoral component typically exhibited a central pivot pattern from extension to 80° relative to the tibial component. From 80° to 120°, bilateral condyles moved backward. In an upright standing position, the femoral component had already rotated externally relative to the tibial component by 7.8±7.5°, and the polyethylene insert had also rotated 8.2°±6.2° externally on the tibial tray.
  
  
  CONCLUSIONS
  The present results demonstrated that mobile-bearing mechanisms with this prosthesis might reduce articular contact stress in vivo.
authors.affiliation: Division of Orthopedic Biomaterial Science, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
authors.forename: Kazuma
authors.initials: K
authors.lastname: Futai
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Tomita
authors.forename: Takaharu
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Masashi
authors.initials: M
authors.lastname: Tamaki
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Kazuomi
authors.initials: K
authors.lastname: Sugamoto
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D017076:Computer-Aided Design; D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D012680:Sensitivity and Specificity; D016474:Weight-Bearing / Q000502:physiology*