title: Crepitus is a first indication of patellofemoral osteoarthritis (and not of tibiofemoral osteoarthritis).
abstract: OBJECTIVE
  The patellofemoral joint (PFJ) is important in early detection of knee osteoarthritis (OA). Little is known about the relationship between specific clinical findings and PFJ Magnetic resonance Imaging (MRI) features. The objective was to examine the relationship between (early) clinical findings and PFJ MRI features in females (45-60 years) without knee OA (PFJ or tibiofemoral joint (TFJ) OA) based on a recently suggested MRI definition.
  
  
  METHODS
  MRIs of knees of women of a sub-study of the Rotterdam Study were scored with semi-quantitative scoring. Specific patellar tests were performed on physical examination. Current knee pain and history of patellar knee pain were reported. Binomial logistic generalized estimated equations were used to determine the association between clinical findings of OA and PFJ MRI features. All associations were adjusted for age, body mass index (BMI) and TFJ MRI features.
  
  
  RESULTS
  In 888 women (1776 knees, mean age: 55.1 years and mean BMI: 27.0 kg/m(2)) we found significant associations between crepitus and all PFJ MRI features (Odds ratios (OR) range: 2.61-5.49). A history of patellar pain was significantly associated with almost all PFJ MRI features (ORcartilage: 1.95; ORcysts: 1.86; ORbone marrow lesions: 1.83), except for osteophytes. No significant associations were found between the clinical findings and TFJ MRI features.
  
  
  CONCLUSIONS
  Crepitus and history of patellar pain are clinical findings that indicate PFJ lesions seen on MRI. These tests could help to indicate signs of PFJOA. Follow-up data needs to confirm whether these tests have an additional diagnostic value for early knee OA in PFJ or TFJ.
authors.affiliation: Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: d.schiphof@erasmusmc.nl.
authors.forename: D
authors.initials: D
authors.lastname: Schiphof
authors.affiliation: Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: m.vanmiddelkoop@erasmusmc.nl.
authors.forename: M
authors.initials: M
authors.lastname: van Middelkoop
authors.affiliation: Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: biancabdk81@gmail.com.
authors.forename: B M
authors.initials: BM
authors.lastname: de Klerk
authors.affiliation: Department of Radiology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: e.oei@erasmusmc.nl.
authors.forename: E H G
authors.initials: EH
authors.lastname: Oei
authors.affiliation: Department of Epidemiology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: a.hofman@erasmusmc.nl.
authors.forename: A
authors.initials: A
authors.lastname: Hofman
authors.affiliation: Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: b.koes@erasmusmc.nl.
authors.forename: B W
authors.initials: BW
authors.lastname: Koes
authors.affiliation: Department of Orthopaedics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands; Department of Orthopaedics, UMC Utrecht, Utrecht, The Netherlands; Department of Rheumatology, UMC Utrecht, Utrecht, The Netherlands. Electronic address: hweinans@umcutrecht.nl.
authors.forename: H
authors.initials: H
authors.lastname: Weinans
authors.affiliation: Department of General Practice, Erasmus MC, University Medical Center, Rotterdam, The Netherlands; Department of Orthopaedics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Electronic address: s.bierma-zeinstra@erasmusmc.nl.
authors.forename: S M A
authors.initials: SM
authors.lastname: Bierma-Zeinstra
mesh_terms: D015992:Body Mass Index; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008875:Middle Aged; D015588:Observer Variation; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000175:diagnosis; D010146:Pain / Q000209:etiology; D057071:Patellofemoral Joint / Q000473:pathology*; D010808:Physical Examination / Q000379:methods; D013016:Sound; D013352:Subcutaneous Emphysema / Q000209:etiology*
keywords: Crepitus; MRI; Pain; Patellofemoral osteoarthritis