Study Design: Retrospective comparative study.

Purpose: To evaluate whether prone traction radiographs provide additional value over prone neutral and erect radiographs in guiding lower instrumented vertebra (LIV) selection in adolescent idiopathic scoliosis (AIS).

Overview of Literature: Accurate LIV selection in AIS is essential to balance deformity correction with motion preservation. Radiographic landmarks such as the last touched vertebra (LTV) and last substantially touched vertebra (LSTV) are commonly used. Prone traction imaging may better demonstrate curve flexibility and potentially allow shorter fusion constructs, but its clinical utility remains incompletely defined.

Methods: AIS patients who underwent posterior spinal fusion between January 2020 and August 2024 were retrospectively reviewed. Patients were stratified into prone neutral (PN, n=55) and prone traction (PT, n=46) cohorts based on preoperative planning protocol. Radiographic parameters (including Cobb angles, LTV, and LSTV) were measured by 3 blinded observers. Vertebral levels saved were calculated relative to erect LSTV. Distal adding-on (AO) was assessed at ≥12 months follow-up.

Results: A total of 101 patients were included with comparable baseline characteristics. PT imaging demonstrated greater curve correction than PN (erect-to-prone ratios: proximal thoracic 0.787 vs 0.914, main thoracic 0.655 vs 0.783, lumbar 0.638 vs 0.749). Fusion proximal to erect LSTV occurred more frequently in the PT group (65.2%) than PN (40.0%). At least one level was saved in 43.5% of PT patients versus 29.1% of PN patients. Distal AO was rare (2.0%), occurring in 2 PT patients.

Conclusions: Prone neutral and prone traction radiographs can both assist in guiding distal fusion level selection in AIS. Prone traction imaging was associated with greater vertebral level preservation in this cohort, with a low observed rate of distal adding-on.