title: Is there an association between superolateral Hoffa fat pad edema on MRI and clinical evidence of fat pad impingement?
abstract: OBJECTIVE
  Patients with symptomatic Hoffa fat pad impingement often exhibit fat pad edema on MRI. We studied two patient groups to determine the association between MRI fat pad edema and clinical symptoms of Hoffa fat pad impingement.
  
  
  METHODS
  We studied 34 consecutive patients with an MRI diagnosis of fat pad edema and no injury in the prior year (group 1) and 47 consecutive patients with a knee MRI examination and no injury in the prior year (group 2). Two sports medicine physicians reviewed the clinical records to confirm or exclude symptomatic fat pad impingement. Two musculoskeletal radiologists independently scored 12 Hoffa fat pad locations for the presence of edema, noting the epicenter.
  
  
  RESULTS
  Seventeen of the 34 patients in group 1 had clinical symptoms of fat pad impingement, with all 34 having fat pad edema. There was no association between clinical fat pad impingement and fat pad edema in any specific location (p > 0.183), but patients with fat pad impingement had a greater number of regions of edema (p = 0.005, 0.026 for two observers). In group 2, all four patients with clinical fat pad impingement had MRI fat pad edema, but 38 of the 43 patients without clinical impingement had MRI fat edema; 11 of the 38 had edema centered in the superolateral fat pad.
  
  
  CONCLUSIONS
  Edema is present on MRI in the superolateral region of Hoffa fat pad in patients with clinical fat pad impingement. However, such edema can also be present in patients without symptoms of fat pad impingement.
authors.affiliation: Department of Radiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Ave, Madison WI 53792, USA. adesmet@uwhealth.org
authors.forename: Arthur A
authors.initials: AA
authors.lastname: De Smet
authors.forename: Kirkland W
authors.initials: KW
authors.lastname: Davis
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Dahab
authors.forename: Donna G
authors.initials: DG
authors.lastname: Blankenbaker
authors.forename: Alejandro Munoz
authors.initials: AM
authors.lastname: del Rio
authors.forename: David T
authors.initials: DT
authors.lastname: Bernhardt
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D001265:Athletic Injuries / Q000150:complications / Q000175:diagnosis*; D002648:Child; D004487:Edema / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000150:complications / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D012189:Retrospective Studies