Proximal Thoracic Alignment Change Influences Cervical Sagittal Alignment After Correction Surgery in Patients With Lenke Type 2 Adolescent Idiopathic Scoliosis.

Objective: To examine the factors influencing cervical sagittal alignment (CSA) after posterior correction and fusion surgery (PSF) for patients with Lenke type 2 adolescent idiopathic scoliosis (AIS).

Methods: A total of 102 female patients with Lenke 2 AIS and a minimum 2-year follow-up were included. The upper instrumented vertebra was T2 in all patients. Sagittal and coronal parameters were measured before and 2 years after surgery. Patients were categorized into cervical malalignment (CM) and noncervical malalignment (NCM) groups following Passias' criteria. Radiographic factors influencing CSA were analyzed.

Results: Preoperatively, 57 patients (55.9%) were assigned to the CM group and 45 patients (44.1%) to the NCM groups. The cervical lordosis (CL) in CM group was more kyphotic (19.3° vs. 3.3°), smaller proximal thoracic kyphosis (PTK; 9.7° vs. 15.4°), and smaller T1 slope (7.1° vs. 14.0°) than those in the NCM group. Main thoracic kyphosis (MTK) did not show significantly difference between the 2 groups (11.3° vs. 14.4°). Two years after surgery, the CM group demonstrated significant improvements in CSA. PTK increased from 9.7° to 13.5°, T1 slope increased from 7.1° to 10.5°, and cervical kyphosis improved from -19.3° to -8.8°, while MTK remained unchanged (11.3° vs. 11.6°).

Conclusion: PSF significantly improved CSA in patients with preoperative CM. Increased PTK, correlated with improved CL, suggests that PSF-induced PTK enhancement, rather than MTK, drives T1 slope and subsequent CSA improvement.