A comparison of the portable DIERS Postura prototype and the stationary DIERS Formetric system for radiation-free spinal reconstruction

Purpose The DIERS Postura reconstructs spinal curvature from back surface topography using an algorithm derived from the established DIERS Formetric . By replacing rasterstereography with an Azure Kinect depth camera, it offers a cost-efficient, portable alternative. This study assesses how this change affects Postura′s reliability and its agreement with Formetric to identify potential systematic errors. Methods Measurements were taken consecutively with the Postura and Formetric while the subjects maintained the same posture. Thirty-one subjects without spinal deformity were evaluated in habitual standing, with four sets of measurements per subject. Three landmarks were marked using reflective markers. Eleven spinal parameters calculated as outputs by both systems were analyzed using Intraclass Correlation Coefficient (ICC), Standard Error of Measurement (SEM), and Smallest Detectable Change (SDC). System agreement was assessed using the Bland-Altman method. Results The non-commercial Postura prototype (2021) showed moderate reliability for two parameters, good reliability for eight, and excellent reliability for one. SDC ranged from 0.52° to 5.11° for measured angles and from 2.06 mm to 7.46 mm for lengths. The agreement analysis showed for eight parameters a mean difference of less than 1°/1 mm, with Limits of Agreement (LoA) up to 5.6° and 8.3 mm. The kyphotic angle showed highest discrepancies, with an SDC of 5.11°, mean difference of −8.88°, and LoA of 10.70°. Conclusion Systematic errors were found in the determination of the spinous process line (SPL) and kyphotic angle. They were caused by the incompatibility of reflective markers with Postura's depth sensor. However, for parameters not directly relying on the SPL, Postura achieved Formetric′s reliability classification for four parameters, one classification lower for others, and good inter-system agreement for eight parameters. This study represents the only evaluation of a Postura system to date, providing insight into its accuracy and limitations, and a framework for the further validation of the released commercial version.