Background: Evaluating curve progression in adolescent idiopathic scoliosis (AIS) patients involves repeated exposure to radiation. Rasterstereography is reported to be a reliable, valid alternative to classic radiography. Few studies have evaluated rasterstereography's responsiveness in detecting curve progression over time or how brace treatment might influence these results.

Objective: The present study aimed to evaluate rasterstereography and scoliometer measurement responsiveness in detecting curve progression in a large cohort of AIS patients with a follow-up time of > 6 months and comparing brace-treated and non-braced patients.

Methods: We included consecutively AIS patients who underwent same-day rasterstereography, scoliometer and radiography evaluations from 2016 to 2018, with at least 6 months between visits. Each patient's major scoliosis curve was evaluated using their Cobb angle (CA) from radiography, their scoliosis angle (SA) from rasterstereography and their axial trunk rotation (ATR) angle from scoliometer measurement. Patients were separated into brace-treated and non-braced groups. Progressive curves were defined by an increase in CA ≥ 5°. The area under the curve (AUC) of non-parametric receiver operating characteristics (ROC) curves was used to assess responsiveness of SA and ATR in detecting progressive curves. We reported sensitivity and specificity.

Results: One-hundred-and-eleven AIS patients (55 brace-treated, 56 non-braced) were evaluated, of whom 17 (16%) had progressive curves: 10/55 (18%) brace-treated and 7/56 (13%) non-braced patients. We found poor AUC and sensitivity (< 50%) in detecting progressive curves among brace-treated patients. However, we found a good AUC (> 75%) and moderate sensitivity (< 70%) in detecting progressive curves among non-braced patients.

Conclusions: Rasterstereography and scoliometer measurements both showed poor and moderate sensitivity in detecting curve progression in brace-treated and non-braced AIS patients, respectively. This suggests that rasterstereography should not be used to monitor curve progression among AIS patients to reduce their exposure to radiation, particularly among brace-treated patients. Presents results adds to ongoing debates about surface topography's role in AIS monitoring, particularly for braced patients where torso shape changes may confound measurements. Although rasterstereography and scoliometer lacks sufficient sensitivity to serve as a standalone monitoring tool, these results identify untreated patients as the most promising target population for future technological refinements of surface topography.