title: In vitro kinematic measurements of the patellar tendon in two different types of posterior-stabilized total knee arthroplasties.
abstract: BACKGROUND
  Fixed-bearing posterior-stabilized (PS) total knee arthroplasty (TKA) has been used in Asian countries for several years, but few studies have investigated differences in the kinematic properties of the patellar tendon after standard PS TKA as compared to high-flex PS TKA.
  
  
  OBJECTIVE
  To quantify the in vitro three-dimensional (3D) kinematics of the patellar tendon during passive high flexion and full extension before and after two different types of PS TKAs.
  
  
  METHODS
  Six fresh-frozen cadaveric knees were tested under the following conditions: the unaltered state, status-post traditional PS prostheses (Simth-nephew GENESIS II) replacement, and status-post high-flexion PS prostheses replacement. The soft tissue around the knee and the quadriceps muscle were preserved, then tested under the load of a specific weight in an Oxford knee rig. We designed a specialized rigid body with four active markers fixed to each bone to track the 3D passive motion of the cadaveric knees. Flexion and extension was controlled by the knee rig and captured by an Optotrak Certus high precision optical tracking system. The attachment sites of the patellar tendon were registered as virtual markers to calculate the 3D kinematics.
  
  
  RESULTS
  The patellar tendon of the unaltered knee and both TKA knees showed similar deformation. We found the length of the patellar tendon changed significantly during a motion from full extension to 30°, but there was no significant change in length while undergoing a motion from 30° to full flexion. Both the sagittal plane and coronal plane angles of the patellar tendon decreased after PS TKAs. There was no significant difference in patellar tendon kinematics between the two types of PS TKAs.
  
  
  CONCLUSIONS
  We believe the changes observed in the sagittal plane and coronal plane angles of the patellar tendon after PS TKAs may influence the extensor mechanism and be an important cause of patella-femoral complications. These data may be used to assess patella-femoral complications after surgery so as to improve the design of high-flexion TKAs for Asians and achieve long-term stability.
authors.affiliation: Department of Biomedical Engineering, Tsinghua University, 100084, China.
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Zhu
authors.forename: Hui
authors.initials: H
authors.lastname: Ding
authors.forename: Xiao
authors.initials: X
authors.lastname: Dang
authors.forename: Jing
authors.initials: J
authors.lastname: Tang
authors.forename: Yixin
authors.initials: Y
authors.lastname: Zhou
authors.forename: Guangzhi
authors.initials: G
authors.lastname: Wang
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D066298:In Vitro Techniques; D018482:Muscle, Skeletal / Q000503:physiopathology; D017847:Patellar Ligament / Q000503:physiopathology*