title: Dynamic in vitro measurement of patellar movement after total knee arthroplasty: an in vitro study.
abstract: BACKGROUND
  Changing the kinematic behaviour of patellar movement could be one of the reasons for anterior knee pain after implantation of a total knee arthroplasty (TKA). The aim of the current study was to measure the potential influence on patellar kinematics of patellar resurfacing during TKA.
  
  
  METHODS
  Patellar movement before and after TKA with and without patellar resurfacing was measured under dynamic conditions in an in vitro cadaver simulation. Physiologic Musculus quadriceps forces were applied to five physiologic human knee specimens undergoing simulated isokinetic extension motions, patellar movement was measured using an ultrasonic measurement system. Thereafter, the Interax I.S.A.-prosthesis system was implanted without and with resurfacing the patella, and patellar movement was again measured.
  
  
  RESULTS
  The physiologic patella center moved on a semilunar path up to 6.4 mm (SD 6.4 mm) medially during extension. After TKA, the unresurfaced patella showed significantly less medial translation (p = 0.04) than the resurfaced patella. Subsequent resurfacing of the patella then resulted in a return to mediolateral positioning of the patella similar to the physiological case, whereas the resurfaced patella tilted up to twice as much as physiologic.
  
  
  CONCLUSIONS
  The results of this study suggest that resurfacing of the patella during TKA can result in a restoration of the physiologic mediolateral shift of the patellofemoral joint while angulation of the patella remains unphysiologic.
authors.affiliation: Department of Orthopaedics, Hannover Medical School (MHH), Hannover, Germany. sven.ostermeier@annastift.de
authors.forename: Sven
authors.initials: S
authors.lastname: Ostermeier
authors.forename: Olaf
authors.initials: O
authors.lastname: Buhrmester
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
authors.forename: Christina
authors.initials: C
authors.lastname: Stukenborg-Colsman
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D066298:In Vitro Techniques; D008875:Middle Aged; D009068:Movement; D010329:Patella / Q000503:physiopathology*; D011184:Postoperative Period; D013499:Surface Properties