title: Differences in subchondral bone size after one year in osteoarthritic and healthy knees.
abstract: OBJECTIVE
  Increase of subchondral bone area (tAB) in OA has been reported, but it remains unclear if this is specific to OA. We investigated differences in knee tAB after one year in healthy subjects and in those with radiographic OA (rOA).
  
  
  METHODS
  MR images of 899 right knees from the OA Initiative were acquired at baseline and one year follow-up (year-1). Medial and lateral tibial cartilage (MT and LT) and weight-bearing femoral cartilage (cMF and cLF) were segmented and tAB computed. Subjects were stratified into: healthy controls, pre-rOA (K&L grades 0 and 1, with OA risk factors), established rOA (K&L grades 2-4), and independently with regards to joint space narrowing (without, with medial, lateral and bilateral JSN). Primary analysis tested if tAB was different between baseline and year-1 in rOA. Exploratory analyses investigated whether: (1) tAB changes differed between healthy controls and those with rOA; (2) tAB differences were greater in higher K&L grades; and (3) tAB was different between baseline and year-1 in JSN. Significance was set at P < 0.0125.
  
  
  RESULTS
  Differences in tAB were found in rOA in MT, cMF and cLF (ranging from +0.2% to +0.4%; P < 0.001), but not in healthy controls or pre-rOA. Rates of change did not differ between groups. Within the JSN groups differences of 0.2-0.4% were found in the femur (P < 0.05).
  
  
  CONCLUSIONS
  We find that knee tABs differ in rOA between baseline and year-1, but the change was not greater than in healthy knees, and is restricted to the femur in JSN.
authors.affiliation: Institute of Anatomy & Musculoskeletal Research, Paracelsus Medical University (PMU), Salzburg, Austria; Chondrometrics GmbH, Ainring, Germany. Electronic address: martin.hudelmaier@pmu.ac.at.
authors.forename: M
authors.initials: M
authors.lastname: Hudelmaier
authors.affiliation: Institute of Anatomy & Musculoskeletal Research, Paracelsus Medical University (PMU), Salzburg, Austria; Chondrometrics GmbH, Ainring, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Wirth
mesh_terms: D000368:Aged; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology*; D016022:Case-Control Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology*; D011859:Radiography; D012720:Severity of Illness Index; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology
keywords: Magnetic resonance imaging; Osteoarthritis; Sensitivity to change; Subchondral bone size