title: Increased patellofemoral pressure after TKA: an in vitro study.
abstract: OBJECTIVE
  Considering the discrepant results of the recent biomechanical studies, the purpose of this study was to simulate dynamic muscle-loaded knee flexion with a large number of specimens and to analyse the influence of total knee arthroplasty (TKA) without and with patellar resurfacing on the patellofemoral pressure distribution.
  
  
  METHODS
  In 22 cadaver knee specimens, dynamic muscle-loaded knee flexion (15°-90°) was simulated with a specially developed knee simulator applying variable muscle forces on the quadriceps muscles to maintain a constant ankle force. Patellofemoral pressures were measured with flexible, pressure-sensitive sensor foils (TEKSCAN) and patellofemoral offset with an ultrasound motion-tracking system (ZEBRIS). Measurements were taken on the native knee, after total knee arthroplasty and after patellar resurfacing. Correct positioning of the patellar implant was examined radiologically.
  
  
  RESULTS
  The maximal patellofemoral peak pressure partly increased from the native knee to the knee with TKA with intact patella (35°-90°, p < 0.012) and highly increased (twofold to threefold) after patellar resurfacing (20°-90°, p < 0.001). Concurrently, the patellofemoral contact area decreased and changed from a wide area distribution in the native knee, to a punctate area after TKA with intact patella and a line-shaped area after patellar resurfacing. Patellar resurfacing led to no increase in patellar thickness and patellofemoral offset.
  
  
  CONCLUSIONS
  Despite correct implantation of the patellar implants and largely unchanged patellofemoral offset, a highly significant increase in pressure after patellar resurfacing was measured. Therefore, from a biomechanical point of view, the preservation of the native patella seems reasonable if there is no higher grade patellar cartilage damage.
authors: Department of Orthopaedic Surgery, University Hospital Tübingen, Hoppe-Seyler-Straße 3, 72076, Tübingen, Germany.
authors: Ulf G
authors: UG
authors: Leichtle
authors: Markus
authors: M
authors: Wünschel
authors: Carmen I
authors: CI
authors: Leichtle
authors: Otto
authors: O
authors: Müller
authors: Philipp
authors: P
authors: Kohler
authors: Nikolaus
authors: N
authors: Wülker
authors: Andrea
authors: A
authors: Lorenz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D001696:Biomechanical Phenomena; D006801:Humans; D066298:In Vitro Techniques; D007720:Knee Prosthesis; D008953:Models, Anatomic; D010329:Patella / Q000601:surgery*; D057071:Patellofemoral Joint / Q000502:physiology* / Q000601:surgery; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing