title: Retropatellar contact characteristics before and after total knee arthroplasty.
abstract: OBJECTIVE
  Qualitative analysis of the retropatellar contact characteristics after total knee arthroplasty.
  
  
  METHODS
  Six cadaveric knees were investigated before and after implantation of a Genesis I knee prosthesis without and with patellar resurfacing in different positions. Joint contact characteristics were evaluated with Fuji Prescale film type 'Super Low' and analyzed qualitatively in nine quadrants. The pressure was determined from a 5-s loading duration in four different knee positions between 45 degrees and 120 degrees of flexion. The femoral component of the prosthesis was implanted in neutral as well as in internal and external rotation. A quadriceps force of 280 N with either a predominant medial or lateral pulling direction was applied.
  
  
  RESULTS
  Without prosthesis the largest contact area is between 60 degrees and 90 degrees of flexion. A lateral muscle force direction as well as an external rotation increased the frequency of loading in the medial quadrants. After implantation of the prosthesis the central and superior quadrants were predominantly contacted irrespective of the flexion angle. No marked differences between the flexion angles were found. Implantation of the patellar resurfacing led to contact in the three central quadrants.
  
  
  CONCLUSIONS
  Implantation of the endoprosthesis leads to increased contact in slight and extreme flexion angles. Especially the central areas are increasingly loaded. No predominant influence of the rotation of the femoral component or the direction of the muscle pull was found. An improved distribution of the contact area could not be demonstrated after patellar resurfacing.
authors.affiliation: Orthopaedic Department, University Clinics Münster, Klinik und Poliklinik für Allgemeine Orthopädie, Albert-Schweitzer-Str. 33, D-48149 Münster, Germany. fuchssu@uni-muenster.de
authors.forename: Susanne
authors.initials: S
authors.lastname: Fuchs
authors.forename: Adrian
authors.initials: A
authors.lastname: Skwara
authors.forename: Carsten O
authors.initials: CO
authors.lastname: Tibesku
authors.forename: Dieter
authors.initials: D
authors.lastname: Rosenbaum
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007719:Knee Joint / Q000502:physiology / Q000601:surgery; D007720:Knee Prosthesis; D008875:Middle Aged; D010329:Patella / Q000502:physiology* / Q000601:surgery; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation