The comparability of HR-pQCT bone measurements is improved by scanning anatomically standardized regions

Abstract

Introduction 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. Methods Double-length (2-cm) scans were acquired in 30 adults. We compared measurements from 1-cm subvolumes 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. Results 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. Conclusion 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.

HR-pQCT Measures of Bone Microarchitecture Predict Fracture: Systematic Review and Meta-Analysis

“…Regrettably, there remains a lack of consensus and standardization of methods for HR‐pQCT imaging and analysis, as well as for estimation methods, such as for Ct.Po, Ct.Th, and FEA measures. Only recently has the community coalesced toward scanning a relative position at 4.0% (radius) and 7.3% (tibia) of total bone length in adults to avoid limb length biases that arise when scanning at a fixed position . Although efforts have been made in terms of providing training tools and establishing normative databases, there is an urgent need for the HR‐pQCT community to consolidate current practices and establish standardized and highly reproducible imaging and analysis protocols and reporting guidelines akin to those widely adopted for rodent μCT studies …”

Sex-, Ethnic-, and Age-Specific Centile Curves for pQCT- and HR-pQCT-Derived Measures of Bone Structure and Strength in Adolescents and Young Adults

“…Thus, we use a percent distance of total limb length so as to scan the same relative ROI in each participant at each measurement time point. Using a site that is relative to limb length has also been recommended when using HR‐pQCT to assess adult populations, as this controls measurement bias between individuals who are different heights …”

Volumetric Bone Mineral Density and Failure Load of Distal Limbs Predict Incident Clinical Fracture Independent of FRAX and Clinical Risk Factors Among Older Men

“…HR‐pQCT scans were done using Scanco XtremeCT II machines (Scanco Medical AG, Brüttisellen, Switzerland), which have a nominal voxel size of 61 μm. Centrally trained operators acquired scans of the distal radius (9 mm from the articular surface), distal tibia (22 mm from the articular surface), and diaphyseal tibia (centered at 30% of tibial length, as measured externally from the tibial plateau to the tibial malleolus . The radius from the nondominant arm and the tibia from the ipsilateral leg were scanned except in the case of prior fracture, metal shrapnel or implant, or recent non–weight‐bearing loads >6 weeks.…”

“…Centrally trained operators acquired scans of the distal radius (9 mm from the articular surface), distal tibia (22 mm from the articular surface), and diaphyseal tibia (centered at 30% of tibial length, as measured externally from the tibial plateau to the tibial malleolus. (15) The radius from the nondominant arm and the tibia from the ipsilateral leg were scanned except in the case of prior fracture, metal shrapnel or implant, or recent non-weight-bearing loads >6 weeks. Machines were calibrated prior to being used in the present study, and a single cross-calibration density phantom was circulated among the study sites.…”