title: Patella tracking and patella contact pressure in modular patellofemoral arthroplasty: a biomechanical in vitro analysis.
abstract: BACKGROUND
  In the recent years modular partial knee prosthesis with the opportunity to combine unicompartmental tibiofemoral (UKA) and patellofemoral prosthesis (PFJ) were introduced to the clinics. To date, little is known about the biomechanics of these bi-cruciate retaining prosthetic designs. Aim of this study was to evaluate the influence of a PFJ in bicompartmental arthroplasty (UKA + PFJ) on patella tracking and retropatella pressure distribution.
  
  
  METHODS
  A dynamic in vitro knee kinemator simulating an isokinetic extension cycle of the knee was used on eight knee specimen. Patella tracking and patellofemoral contact pressure were evaluated using pressure sensitive films after implantation of a medial UNI and after subsequent implantation of a PFJ.
  
  
  RESULTS
  Whereas the area contact pressure remained the same after PFJ implantation, the contact area was reduced significantly and significantly elevated peak pressures were determined in deep flexion and close to extension. The patella tracking was not significantly altered, however, effects of edge loading could be shown.
  
  
  CONCLUSIONS
  When using PFJ prosthesis, one must be aware of altered pressure introduction on the retropatella surface compared to the physiological situation. The elevated peak pressures and reduced contact area may be an argument for patella resurfacing and the problems of edge loading indicate that care must be taken on the correct implantation of the device with no implant overhang.
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany. tilman.calliess@ddh-gruppe.de.
authors.forename: Tilman
authors.initials: T
authors.lastname: Calliess
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Ettinger
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany.
authors.forename: Ssuheib
authors.initials: S
authors.lastname: Schado
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Becher
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 3, 30625, Hannover, Germany.|Orthopädische Praxis und Gelenk-Klinik, Alte Bundesstrasse 58, 79194, Gundelfingen, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Ostermeier
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D057071:Patellofemoral Joint / Q000502:physiology* / Q000601:surgery*
keywords: Bicompartmental; Knee arthroplasty; Patella pressure; Patellofemoral; Unicompartmental