title: Reducing the lateral force acting on the patella does not consistently decrease patellofemoral pressures.
abstract: BACKGROUND
  Extensor mechanism procedures that decrease the lateral component of the patellar tendon or quadriceps force acting on the patella do not consistently reduce pain.
  
  
  OBJECTIVE
  Patellofemoral treatments do not consistently decrease patellofemoral pressures because of variations in the moments acting on the patella.
  
  
  METHODS
  Computer simulation study.
  
  
  METHODS
  Computational models of 4 knees were constructed to characterize the patellofemoral pressure distribution during simulated squatting from 40 degrees to 90 degrees. The knees were given an initial Q angle of 25 degrees. Patellofemoral treatments were simulated by increasing the percentage of the quadriceps force applied by the vastus medialis by 50% and by medializing the tibial tuberosity to decrease the Q angle to 15 degrees.
  
  
  RESULTS
  Decreasing the Q angle caused a larger decrease in the lateral component of the force applied by the quadriceps and patellar tendon than did increasing the force applied by the vastus medialis and, therefore, was more effective at decreasing patellofemoral pressures and the force needed to resist lateral subluxation. Both treatments also decreased the moments acting to rotate the distal patella laterally and tilt the patella laterally during flexion. Variations in these moments increased patellofemoral pressures for some knees.
  
  
  CONCLUSIONS
  Treatments that reduce patellofemoral subluxation can have an unexpected influence on patellofemoral pressures because of the moments acting on the patella.
  
  
  CONCLUSIONS
  Extensor mechanism procedures that restore patellofemoral stability may not provide pain relief.
authors.affiliation: Medical Education and Research Institute of Colorado, 3920 North Union Blvd, Suite 210, Colorado Springs, CO 80907, USA. elias@meric.info
authors.forename: John J
authors.initials: JJ
authors.lastname: Elias
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Cech
authors.forename: David M
authors.initials: DM
authors.lastname: Weinstein
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Cosgrea
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D010329:Patella / Q000502:physiology*; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013710:Tendons / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology