title: Using ordered values of subregional cartilage thickness change increases sensitivity in detecting risk factors for osteoarthritis progression.
abstract: OBJECTIVE
  To examine whether ordered values of (sub)regional femorotibial cartilage thickness change are superior to region-based approaches in detecting risk factors for cartilage loss in osteoarthritis (OA).
  
  
  METHODS
  58 women with knee OA had 3 Tesla MR images acquired at baseline and 24 months. Changes in cartilage thickness (∆ThCtAB) were determined in eight medial femorotibial subregions. An ascending sort of individual ∆ThCtAB measurements was done to create "ordered values". Risk factors for cartilage loss considered were: age, BMI, anatomical knee axis (AAA), minimal (medial) joint space width (mJSW), and percent of medial tibial plateau covered by the meniscus (percent cover). All change metrics were tested for association with the risk factors using Kendall's τ and relative sensitivity of multiple tests of subregions and ordered values were compared with single metrics of change from plate and compartment summaries and the first ordered value.
  
  
  RESULTS
  The associations between subregion ∆ThCtAB and AAA (P=0.0002), mJSW (P=0.016), and age (P=0.011) were significant, but only AAA (at α=0.05) and age (at α=0.1) remained significant after adjusting for multiple subregions. In contrast, cMFTC had P-values<0.05 for AAA (P=0.0001), mJSW (P=0.016), and meniscus subluxation (0.04). The first ordered value had significant associations with AAA (P=0.0004), mJSW (P=0.003), meniscus subluxation (P=0.02) and percent cover (P=0.031) all of which were significant at α=0.05 after adjusting for tests on multiple risk factors.
  
  
  CONCLUSIONS
  Ordered values of ∆ThCtAB were more sensitive in detecting risk factors of cartilage loss than subregional ∆ThCtAB. Sensitivity was further enhanced by considering the minimum ordered value as a single test, thus not requiring adjustment for multiple tests. Using ordered values there was a significant association between ∆ThCtAB and baseline AAA, mJSW, meniscus subluxation and meniscus percent cover. This study provides an important step in validating ordered values of cartilage change.
authors.affiliation: StatAnswers Consulting LLC, San Diego, CA 92122, USA. robert.j.buck@gmail.com
authors.forename: R J
authors.initials: RJ
authors.lastname: Buck
authors.forename: B T
authors.initials: BT
authors.lastname: Wyman
authors.forename: M-P
authors.initials: MP
authors.lastname: Hellio Le Graverand
authors.forename: D
authors.initials: D
authors.lastname: Hunter
authors.forename: E
authors.initials: E
authors.lastname: Vignon
authors.forename: W
authors.initials: W
authors.lastname: Wirth
authors.forename: F
authors.initials: F
authors.lastname: Eckstein
mesh_terms: D000368:Aged; D002358:Cartilage, Articular / Q000473:pathology*; D018450:Disease Progression; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000473:pathology*; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index