title: Least significant changes and monitoring time intervals for high-resolution pQCT-derived bone outcomes in postmenopausal women.
abstract: BACKGROUND
  Least Significant Change (LSC) assists in determining whether observed bone change is beyond measurement precision. Monitoring Time Interval (MTI) estimates time required to reliably detect skeletal changes. MTIs have not been defined for bone outcomes provided by high resolution peripheral quantitative computed tomography (HR-pQCT). The purpose of this study was to determine the LSCs and MTIs for HR-pQCT derived bone area, density and micro-architecture with postmenopausal women.
  
  
  METHODS
  Distal radius and tibia of 33 postmenopausal women (mean age: 77, SD: ±7 years), from the Saskatoon cohort of the Canadian Multicentre Osteoporosis Study (CaMos), were measured using HR-pQCT at baseline and 1-year later. We determined LSC from precision errors and divided them by the median annual percent changes to define MTIs for bone area, density, and micro-architecture.
  
  
  RESULTS
  Distal radius: HR-pQCT LSCs indicated a 1-8% observed change was needed for reliable monitoring of bone area and density while a 3-18% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to cortical and trabecular area and density measures, cortical thickness and bone volume fraction; the shortest MTIs (~2 years) pertained to bone micro-architectural measures (trabecular number, thickness, separation and heterogeneity). Distal tibia: LSCs indicated a <1-5% observed change was needed for reliable monitoring of bone area and density, while a 3-19% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to trabecular density, bone volume fraction, number, separation and heterogeneity; the shortest MTIs (~1 year) pertained to cortical and trabecular area, cortical density and thickness.
  
  
  CONCLUSIONS
  MTIs suggest that performing HR-pQCT follow-up measures in postmenopausal women every 2 years at the distal radius and every 1 year at the distal tibia to monitor true skeletal changes as indicated by the LSCs.
authors.affiliation: College of Kinesiology, University of Saskatchewan.
authors.forename: C E
authors.initials: CE
authors.lastname: Kawalilak
authors.affiliation: Department of Mechanical Engineering, College of Engineering, University of Saskatchewan.
authors.forename: J D
authors.initials: JD
authors.lastname: Johnston
authors.affiliation: College of Medicine, University of Saskatchewan.
authors.forename: W P
authors.initials: WP
authors.lastname: Olszynski
authors.affiliation: College of Kinesiology, University of Saskatchewan.
authors.forename: S A
authors.initials: SA
authors.lastname: Kontulainen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001842:Bone and Bones / Q000000981:diagnostic imaging; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D006801:Humans; D008875:Middle Aged; D008991:Monitoring, Physiologic; D015663:Osteoporosis, Postmenopausal / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging; D011884:Radius / Q000000981:diagnostic imaging; D012525:Saskatchewan / Q000453:epidemiology; D013977:Tibia / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed