Upper Instrumented Vertebra Selection Influences Proximal Balance but Not Long-Term Clinical Outcomes in Lenke Type 1 Adolescent Idiopathic Scoliosis.

Background/Objectives: Selection of the upper instrumented vertebra (UIV) in Lenke type 1 adolescent idiopathic scoliosis (AIS) influences postoperative proximal balance; however, the long-term clinical relevance of radiographic differences remains uncertain. This study evaluated long-term radiological and clinical outcomes in a homogeneous Lenke type 1 AIS cohort undergoing posterior spinal fusion with UIV selection at T2 or T4. Methods: During the study period, 120 consecutive Lenke type 1 AIS patients underwent posterior spinal fusion. Twelve patients who developed major postoperative complications were excluded, resulting in a final cohort of 108 patients (T2: n = 61; T4: n = 47). Patients requiring posterior column osteotomies were excluded to maintain surgical homogeneity. Radiological parameters, including coronal and sagittal alignment, proximal balance measures, and curve flexibility, were assessed preoperatively, postoperatively, and at a minimum follow-up of five years. Clinical outcomes were evaluated using validated Turkish versions of the Pediatric Quality of Life Inventory (PedsQL) and the Scoliosis Research Society-22 revised questionnaire (SRS-22r). Longitudinal within-group changes were analyzed. Results: Substantial correction of the main thoracic curve was achieved postoperatively and maintained at long-term follow-up within each cohort (p < 0.001). Preoperative bending radiographs demonstrated preserved curve flexibility, indicating that postoperative alignment differences were not attributable to baseline rigidity. Proximal coronal and shoulder balance parameters improved over time within each cohort, with residual differences observed according to UIV selection. Psychosocial domains of the PedsQL and SRS-22r improved significantly over time within each cohort. In contrast, PedsQL physical functioning scores declined significantly at long-term follow-up (p < 0.001), consistent with fusion-related stiffness rather than global clinical deterioration. No clinically meaningful divergence in patient-reported outcome trajectories was observed according to the UIV strategy. Conclusions: In Lenke type 1 AIS, UIV selection influences long-term proximal balance-related radiological parameters but does not confer a clinically meaningful advantage in patient-reported outcomes. Both T2 and T4 strategies provide durable deformity correction and sustained multidimensional recovery when guided by individualized criteria. Prospective multicenter investigations are warranted to further clarify the clinical relevance of proximal balance metrics.