title: Is superolateral Hoffa fat pad edema a consequence of impingement between lateral femoral condyle and patellar ligament?
abstract: OBJECTIVE
  To evaluate whether knee extensor mechanism features are associated with superolateral Hoffa fat pad edema at magnetic resonance imaging.
  
  
  METHODS
  Institutional review board approval and written consent from all patients were obtained. Patients with superolateral Hoffa fat pad edema (n = 30) and a control group without edema of the fat pad (n = 60) were evaluated prospectively with magnetic resonance (MR) imaging. Demographic data and extensor mechanism features were compared, including trochlear depth, lateral trochlear inclination, patellar tilt angle, patellar height ratio, distance between patellar ligament and lateral trochlear facet, distance from the tibial tubercle to the trochlear groove, patellar facet asymmetry, and patellar ligament abnormalities.
  
  
  RESULTS
  The following variables were associated with superolateral Hoffa fat pad edema in the multivariable models: patellar height ratio (P = .023), shortest distance between patellar ligament and lateral trochlear facet (P < .001), and distance from the tibial tubercle to the trochlear groove (P = .046). Of all demographic and degenerative variables, only age was significantly associated, with younger patients more likely to have superolateral Hoffa fat pad edema (P < .009).
  
  
  CONCLUSIONS
  A high-riding patella, a short distance between the patellar ligament and the lateral trochlear facet, and an increased distance from the tibial tubercle to the trochlear groove are associated with superolateral Hoffa fat pad edema at MR imaging. These results are suggestive of impingement between the lateral femoral condyle and the posterior aspect of the patellar ligament in these patients.
authors.affiliation: Department of Radiology B, Hôpital Cochin, Université Paris Descartes, Paris, France. rcampagna1@gmail.com
authors.forename: Raphael
authors.initials: R
authors.lastname: Campagna
authors.forename: Eric
authors.initials: E
authors.lastname: Pessis
authors.forename: David Jean
authors.initials: DJ
authors.lastname: Biau
authors.forename: Henri
authors.initials: H
authors.lastname: Guerini
authors.forename: Antoine
authors.initials: A
authors.lastname: Feydy
authors.forename: Fabrice Stéphane
authors.initials: FS
authors.lastname: Thevenin
authors.forename: Etienne
authors.initials: E
authors.lastname: Pluot
authors.forename: Julien
authors.initials: J
authors.lastname: Rousseau
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Drapé
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004487:Edema / Q000175:diagnosis* / Q000209:etiology*; D005269:Femur / Q000473:pathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007592:Joint Diseases / Q000175:diagnosis*; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D017847:Patellar Ligament / Q000473:pathology*; D011446:Prospective Studies; D012044:Regression Analysis