title: Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation.
abstract: OBJECTIVE
  Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.
  
  
  METHODS
  A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.
  
  
  RESULTS
  This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.
  
  
  CONCLUSIONS
  In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.
  
  
  METHODS
  II.
authors.affiliation: Biomechanics Research Laboratory, Mackay Memorial Hospital, New Taipei City, Taiwan.
authors.forename: Chang-Hung
authors.initials: CH
authors.lastname: Huang
authors.forename: Lin-I
authors.initials: LI
authors.lastname: Hsu
authors.forename: Kun-Jhih
authors.initials: KJ
authors.lastname: Lin
authors.forename: Ting-Kuo
authors.initials: TK
authors.lastname: Chang
authors.forename: Cheng-Kung
authors.initials: CK
authors.lastname: Cheng
authors.forename: Yung-Chang
authors.initials: YC
authors.lastname: Lu
authors.forename: Chen-Sheng
authors.initials: CS
authors.lastname: Chen
authors.forename: Chun-Hsiung
authors.initials: CH
authors.lastname: Huang
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D007720:Knee Prosthesis; D057071:Patellofemoral Joint / Q000503:physiopathology*; D011187:Posture / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013977:Tibia / Q000503:physiopathology