title: The comparability of HR-pQCT bone measurements is improved by scanning anatomically standardized regions.
abstract: We investigated the sensitivity of distal bone density, structure, and strength measurements by high-resolution peripheral quantitative computed tomography (HR-pQCT) to variability in limb length. Our results demonstrate that HR-pQCT should be performed at a standard %-of-total-limb-length to avoid substantial measurement bias in population study comparisons and the evaluation of individual skeletal status in a clinical context.
  
  
  
  High-resolution peripheral quantitative computed tomography (HR-pQCT) measures of bone do not account for anatomic variability in bone length: a 1-cm volume is acquired at a fixed offset from an anatomic landmark. Our goal was to evaluate HR-pQCT measurement variability introduced by imaging fixed vs. proportional volumes and to propose a standard protocol for relative anatomic positioning.
  
  
  
  Double-length (2-cm) scans were acquired in 30 adults. We compared measurements from 1-cm sub-volumes located at the default fixed offset, and the average %-of-length offset. The average position corresponded to 4.0% ± 1.1 mm for radius, and 7.2% ± 2.2 mm for tibia. We calculated the RMS difference in bone parameters and T-scores to determine the measurement variability related to differences in limb length. We used anthropometric ratios to estimate the mean limb length for published HR-pQCT reference data, and then calculated mean %-of-length offsets.
  
  
  
  Variability between fixed vs. relative scan positions was highest in the radius, and for cortical bone in general (RMS difference Ct.Th = 19.5%), while individuals had T-score differentials as high as +3.0 SD (radius Ct.BMD). We estimated that average scan position for published HR-pQCT reference data corresponded to 4.0% at the radius, and 7.3% at tibia.
  
  
  
  Variability in limb length introduces significant bias to HR-pQCT measures, confounding cross-sectional analyses and limiting the clinical application for individual assessment of skeletal status. We propose to standardize scan positioning using 4.0 and 7.3% of total bone length for the distal radius and tibia, respectively.
authors.affiliation: Musculoskeletal Quantitative Imaging Research Group, Department of Radiology & Biomedical Imaging, University of California, QB3 Building, Suite 203, 1700 4th St, San Francisco, CA, 94158, USA.|Department of Radiology, Stanford University, Stanford, CA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Bonaretti
authors.affiliation: Musculoskeletal Quantitative Imaging Research Group, Department of Radiology & Biomedical Imaging, University of California, QB3 Building, Suite 203, 1700 4th St, San Francisco, CA, 94158, USA.
authors.forename: S
authors.initials: S
authors.lastname: Majumdar
authors.affiliation: Musculoskeletal Quantitative Imaging Research Group, Department of Radiology & Biomedical Imaging, University of California, QB3 Building, Suite 203, 1700 4th St, San Francisco, CA, 94158, USA.
authors.forename: T F
authors.initials: TF
authors.lastname: Lang
authors.affiliation: Division of Endocrinology, Metabolism and Nutrition, Department of Internal Medicine, College of Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: S
authors.initials: S
authors.lastname: Khosla
authors.affiliation: Musculoskeletal Quantitative Imaging Research Group, Department of Radiology & Biomedical Imaging, University of California, QB3 Building, Suite 203, 1700 4th St, San Francisco, CA, 94158, USA. andrew.burghardt@ucsf.edu.
authors.forename: A J
authors.initials: AJ
authors.lastname: Burghardt
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks; D000886:Anthropometry / Q000379:methods; D015519:Bone Density / Q000502:physiology*; D005260:Female; D020342:Finite Element Analysis; D005542:Forearm / Q000033:anatomy & histology; D006801:Humans; D007866:Leg / Q000033:anatomy & histology; D008297:Male; D011884:Radius / Q000000981:diagnostic imaging* / Q000502:physiology; D015203:Reproducibility of Results; D013977:Tibia / Q000000981:diagnostic imaging* / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000379:methods* / Q000592:standards
keywords: Bone; HR-pQCT; Multicenter study; Osteoporosis; Precision; Standardization