title: Intraoperative vs. weightbearing patellar kinematics in total knee arthroplasty: a cadaveric study.
abstract: BACKGROUND
  During knee replacement surgery, surgeons optimize intraoperative patellar tracking with the aim of optimizing postoperative tracking. This link has not been investigated to date. Our research questions were: (1) How well do patellar kinematics correlate between passive and weightbearing flexion across numerous changes in component placement? (2) How do the kinematics differ between the two loading configurations?
  
  
  METHODS
  Eight cadaveric knee joints with modified knee components that allowed 11 different femoral, tibial and patellar placements were tested in two experimental rigs simulating intraoperative and weightbearing dynamic flexion. Baseline placement had all components in neutral position. Pearson correlation coefficients were calculated for absolute baseline kinematics and for relative kinematics due to changes in component position (i.e., the 10 altered positions vs. baseline).
  
  
  RESULTS
  Correlations between intraoperative and weightbearing rigs for absolute baseline kinematics were unpredictable, ranging from poor to excellent (mean 0.56 for tilt and mean 0.50 for shift). Correlations between rigs for changes in tilt and shift, i.e. relative kinematics, were strong (>0.8) or very strong (>0.9), with the exception of shift in early flexion (0.54). Differences in relative kinematics, which averaged 2.2 degrees in tilt (standard deviation 1.8 degrees ) and 1.6mm in shift (standard deviation 1.7mm), were notably smaller and less variable than differences in absolute kinematics, which averaged 4.2 degrees in tilt (standard deviation 3.6 degrees ) and 4.3mm in shift (standard deviation 3.9mm).
  
  
  CONCLUSIONS
  The results of this study suggest that, while absolute kinematics may differ between conditions, if a surgeon adjusts a component position to improve patellar kinematics intraoperatively, the effects of such a geometric change will likely carry through to the postoperative joint.
authors.affiliation: Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada. canglin@ucalgary.ca
authors.forename: C
authors.initials: C
authors.lastname: Anglin
authors.forename: J M
authors.initials: JM
authors.lastname: Brimacombe
authors.forename: D R
authors.initials: DR
authors.lastname: Wilson
authors.forename: B A
authors.initials: BA
authors.lastname: Masri
authors.forename: N V
authors.initials: NV
authors.lastname: Greidanus
authors.forename: J
authors.initials: J
authors.lastname: Tonetti
authors.forename: A J
authors.initials: AJ
authors.lastname: Hodgson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D002102:Cadaver; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000502:physiology*; D011897:Random Allocation; D025321:Surgery, Computer-Assisted; D016474:Weight-Bearing