title: Knee pain and inflammation in the infrapatellar fat pad estimated by conventional and dynamic contrast-enhanced magnetic resonance imaging in obese patients with osteoarthritis: a cross-sectional study.
abstract: OBJECTIVE
  To investigate the association between knee pain and signs of inflammation in the infrapatellar fat pad (IPFP) in obese patients with knee osteoarthritis (KOA).
  
  
  METHODS
  In a cross-sectional setting, 3-T conventional contrast-enhanced (CE) magnetic resonance imaging (MRI) and dynamic contrast-enhanced (DCE)-MRI of KOA were analysed to quantify the extent of inflammation in the IPFP, and correlated (Spearman's rank correlation) to pain and other symptoms assessed via the Knee injury and Osteoarthritis Outcome Score (KOOS) (100 = no pain, 0 = extreme pain). The extent of inflammation in the IPFP was assessed according to the MRI Osteoarthritis Knee Score (MOAKS) using CE-MRI and by DCE-MRI perfusion variables. The perfusion variable, "Inflammation", was chosen as primary perfusion variable in the analysis. Intraclass correlation coefficients for the perfusion variables ranged from 0.81 to 0.99.
  
  
  RESULTS
  MRI and clinical data were obtained in 95 patients. The typical patient was a woman (82%) with an average age of 65 years (SD 6.5) and a body mass index (BMI) of 32 kg/m(2) (SD 3.7). The bivariate association between KOOS pain and the DCE-MRI perfusion variable "Inflammation" showed a statistically significant correlation (r = -0.42, P < 0.0001). A statistically significant correlation was also found between KOOS pain and MOAKS Hoffa-synovitis (r = -0.21, P = 0.046).
  
  
  CONCLUSIONS
  Perfusion variables on DCE-MRI reflecting the severity of inflammation in the IPFP and MOAKS Hoffa-synovitis were associated with the severity of pain in KOA. These results suggest that severe inflammation in the IPFP is associated with severe pain in KOA and that DCE-MRI is a promising method to study the impact of inflammation in KOA.
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: christine_ballegaard@hotmail.com.
authors.forename: C
authors.initials: C
authors.lastname: Ballegaard
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark; Department of Radiology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: robert.gabriel.riis@regionh.dk.
authors.forename: R G C
authors.initials: RG
authors.lastname: Riis
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: henning.bliddal@frh.regionh.dk.
authors.forename: H
authors.initials: H
authors.lastname: Bliddal
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark; Institute of Sports Science and Clinical Biomechanics, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark. Electronic address: robin.christensen@frh.regionh.dk.
authors.forename: R
authors.initials: R
authors.lastname: Christensen
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: marius.henriksen@regionh.dk.
authors.forename: M
authors.initials: M
authors.lastname: Henriksen
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: else.marie.bartels@regionh.dk.
authors.forename: E M
authors.initials: EM
authors.lastname: Bartels
authors.affiliation: Institute of Sports Science and Clinical Biomechanics, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark; Department of Orthopaedics, Clinical Sciences Lund, Lund University, Sweden; Department of Orthopaedics and Traumatology, University of Southern Denmark, Odense, Denmark. Electronic address: stefan.lohmander@med.lu.se.
authors.forename: L S
authors.initials: LS
authors.lastname: Lohmander
authors.affiliation: Rheumatology Department, Royal North Shore Hospital and Kolling Institute, University of Sydney, NSW, Australia. Electronic address: david.hunter@sydney.edu.au.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hunter
authors.affiliation: Department of Radiology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: rasmus.bouert@regionh.dk.
authors.forename: R
authors.initials: R
authors.lastname: Bouert
authors.affiliation: The Parker Institute, Department of Rheumatology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark; Department of Radiology, Copenhagen University Hospital, Bispebjerg-Frederiksberg, Copenhagen F, Denmark. Electronic address: mikael.boesen@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Boesen
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000368:Aged; D018771:Arthralgia / Q000473:pathology*; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000473:pathology*; D020370:Osteoarthritis, Knee / Q000473:pathology*; D017063:Outcome Assessment, Health Care; D010329:Patella / Q000473:pathology*; D012720:Severity of Illness Index; D012984:Software; D013585:Synovitis / Q000473:pathology
keywords: Chronic pain; Inflammation; Knee; Magnetic resonance imaging; Osteoarthritis