Impact of coordinate system alignment on CT-based distal radius morphometry relevant to surgical planning: A bilateral comparative study.

Background: Computed tomography-based three-dimensional morphometric analysis is increasingly used for surgical planning and contralateral templating in distal radius surgery. However, the influence of coordinate system alignment on morphometric measurements has not been systematically evaluated. Methods: A cross-sectional imaging study was performed using CT-derived three-dimensional models from 83 healthy Vietnamese adults (166 distal radii). Distal radius width and thickness were measured using two coordinate systems: the default software bounding-box orientation and an anatomically axis-corrected system aligned with the distal radius longitudinal axis. Measurements were compared using paired analyses, and inter-observer reliability was assessed using intraclass correlation coefficients. Results: Width measurements showed no statistically significant differences between the two coordinate systems. In contrast, thickness measurements were consistently greater after anatomical axis correction, with median differences of 0.18 mm on the right and 0.15 mm on the left (both p < 0.001). Inter-observer reliability was excellent for all measurements (ICC = 1.0), reflecting the high reproducibility of the standardized coordinate alignment workflow. Conclusion: Anatomical coordinate system alignment introduces small but consistent differences in CT-based distal radius morphometric measurements, particularly for thickness estimation. Although the absolute differences were small, standardizing coordinate system alignment may improve the reproducibility and comparability of CT-derived measurements used for morphometric analysis, preoperative planning, and contralateral templating. Future CT-based morphometric studies should explicitly describe the coordinate system used for measurement.