title: Presence, location, type and size of denuded areas of subchondral bone in the knee as a function of radiographic stage of OA - data from the OA initiative.
abstract: OBJECTIVE
  To assess the presence, location, type and size of denuded areas of subchondral bone (dAB) in the femorotibial joint, measured quantitatively with 3T MRI, in a large subset of OAI participants.
  
  
  METHODS
  One knee of 633 subjects (250 men, 383 women, aged 61.7+/-9.6 y) were studied, spanning all radiographic osteoarthritis (OA) stages. dABs were determined quantitatively using segmentations of coronal FLASHwe images, representing areas where the subchondral bone was not covered by cartilage. Post hoc visual examination of segmented images determined whether dABs represented full thickness cartilage loss or internal osteophyte.
  
  
  RESULTS
  7% Of the knees were Kellgren & Lawrence (KL) grade 0, 6% grade 1, 41% grade 2, 41% grade 3, and 5% grade 4. 39% Of the participants (48% of the men and 33% of the women) displayed dABs; 61% of the dABs represented internal osteophytes. 1/47 Participants with KL grade 0 displayed 'any' dAB whereas 29/32 of the KL grade 4 knees were affected. Even as early as KL grade 1, 29% of the participants showed dABs. There were significant relationships of dAB with increasing KL grades (P<0.001) and with ipsi-compartimental JSN (P< or =0.001). Internal osteophytes were more frequent laterally (mainly posterior tibia and internal femur) whereas full thickness cartilage loss was more frequent medially (mainly external tibia and femur).
  
  
  CONCLUSIONS
  dABs occur already at earliest stages of radiographic OA (KL grades 1 and 2) and become more common (and larger) with increasing disease severity. Almost all KL grade 4 knees exhibited dABs, with cartilage loss being more frequent than internal osteophytes.
authors.affiliation: Institute of Anatomy and Musculoskeletal Research, Paracelsus Medical University, Salzburg, Austria. richard.frobell@pmu.ac.at
authors.forename: R B
authors.initials: RB
authors.lastname: Frobell
authors.forename: W
authors.initials: W
authors.lastname: Wirth
authors.forename: M
authors.initials: M
authors.lastname: Nevitt
authors.forename: B T
authors.initials: BT
authors.lastname: Wyman
authors.forename: O
authors.initials: O
authors.lastname: Benichou
authors.forename: D
authors.initials: D
authors.lastname: Dreher
authors.forename: R Y
authors.initials: RY
authors.lastname: Davies
authors.forename: J H
authors.initials: JH
authors.lastname: Lee
authors.forename: F
authors.initials: F
authors.lastname: Baribaud
authors.forename: A
authors.initials: A
authors.lastname: Gimona
authors.forename: M
authors.initials: M
authors.lastname: Hudelmaier
authors.forename: S
authors.initials: S
authors.lastname: Cotofana
authors.forename: F
authors.initials: F
authors.lastname: Eckstein
mesh_terms: D000368:Aged; D002358:Cartilage, Articular / Q000473:pathology*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D011859:Radiography