title: Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome.
abstract: BACKGROUND
  An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis.
  
  
  METHODS
  Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell.
  
  
  RESULTS
  Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%.
  
  
  CONCLUSIONS
  An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-Von-Borries-Str. 1-7, 30625, Hannover, Germany. bohnsack@annastift.de
authors.forename: Michael
authors.initials: M
authors.lastname: Bohnsack
authors.forename: Phillip
authors.initials: P
authors.lastname: Klages
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
authors.forename: Andre
authors.initials: A
authors.lastname: Halcour
authors.forename: Arne
authors.initials: A
authors.lastname: Wilharm
authors.forename: Sven
authors.initials: S
authors.lastname: Ostermeier
authors.forename: Oliver
authors.initials: O
authors.lastname: Rühmann
authors.forename: Carl-Joachim
authors.initials: CJ
authors.lastname: Wirth
mesh_terms: D000273:Adipose Tissue; D000328:Adult; D001178:Arthroplasty / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D002102:Cadaver; D004487:Edema / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008953:Models, Anatomic; D046788:Patellofemoral Pain Syndrome / Q000209:etiology