Appraisal of the DIERS method for calculating postural measurements: an observational study

BACKGROUND Surface topography is increasingly used with postural analysis. One system, DIERS formetric 4D, measures 40 defined spine shape parameters from a 6-s scan. Through system algorithms, a set of spine shape parameter values from 1 of 12 recorded images obtained during a scan becomes the DIERS-reported value (DRV) for postural assessment. The purpose of the current study was to compare DRV with a standard average value (SAV) calculated from all 12 images to determine which method is more appropriate for assessing postural change. METHODS One mannequin and 30 human participants were scanned over 5 days. Values from each image and the DRV for 40 defined spine shape parameters were exported, and mean DRV, mean SAV, mean DRV, and within-scan variance were calculated. Absolute difference and percent change between mean DRV and mean SAV were calculated for the mannequin and humans. Inter-method reliability was calculated for humans. Within-scan variance for each parameter was tested for significant variability. RESULTS For all spine shape parameters on the mannequin, absolute difference (< 0.6 mm, 0.1°, or 0.1%) and percent change (< 2.90%) between mean DRV and mean SAV for each parameter were small. Nine parameters on human participants had a large percent change (> 7%). Absolute difference between mean DRV and mean SAV for those nine parameters was small (≤ 0.87 mm or 0.61°). Absolute difference for all other parameters ranged from 0.02 to 6.98 mm for distance measurements, from 0.01 to 1.21° for angle measurements, and from 0.15 to 0.22% for percentage measurements. Inter-method reliability between DRV and SAV was excellent (0.94-1.00). For the mannequin, within-scan variance was small (< 1.62) for all parameters. For humans, within-scan variance ranged from 0.05 to 36.04 and was different from zero for all parameters (all P < 0.001). CONCLUSIONS The minimal variability observed in the mannequin suggested the DIERS formetric 4D instrument had high within-scan reliability. The DRV and SAV provided comparable spine shape parameter values. Because within-scan variability is not reported with the DRV, the clinical usefulness of current DRV values is limited. Establishing an estimate of variance with the SAV will allow clinicians to better identify a clinically meaningful change.