Clinical relevance among optical, ultrasonic, and radiographic imaging in scoliosis assessment.

PURPOSE: Although optical (OPI) and ultrasonic imaging (USI) have each been independently investigated as non-invasive alternatives to radiography (Xray) in scoliosis assessment, no study has yet directly compared their clinical performance. This study aimed to evaluate the clinical agreement and validity of OPI and USI, using Xray as the reference standard.

METHODS

Radiographic Cobb angle served as the gold standard for clinical evaluation of two non-invasive methods. The OPI-angle was derived from spine models fitted to digitised surface data based on structured-light, while USI-angle was measured from images acquired using an ultrasonic system. All scans were performed in the same upright posture. For analysis, 14 participants with suspected scoliosis completed all three assessments (Xray, OPI, USI) for direct three-way comparison. Additionally, 29 participants underwent Xray and OPI, and 25 underwent Xray and USI, enabling respective pairwise comparisons with the radiographic Cobb angle. The correlation, agreement, and measurement error were evaluated, with subgroup analyses based on spinal region, curve severity, and apical vertebral rotation (AVR) level.

RESULTS

Both non-invasive methods showed strong correlations with the radiographic Cobb angle (OPI: r = 0.873, 95% CI: 0.734-0.938; USI: r = 0.902, 95% CI: 0.791-0.953), with mean absolute differences (MADs) of 4.3° and 4.2°, respectively. The correlation between OPI- and USI-angles was r = 0.795 (95% CI: 0.590-0.898). Subgroup analyses revealed stronger correlations in the thoracic compared to the lumbar region for both methods. USI-angle showed a smaller MAD in mild than in moderate curves (4.3° vs. 7.1°). Optimal performance for both methods was observed at 5-10° AVR (OPI: MAD = 3.9°, r = 0.846; USI: MAD = 5.2°, r = 0.835).

CONCLUSIONS

Both OPI and USI demonstrated strong agreement with radiographic measurements in scoliosis assessment, supporting their potential as useful non-invasive tools for clinical screening and monitoring applications. Additional validation with larger sample sizes, different severities, and various body mass index levels is required to further improve their clinical efficacy and applicability.