Does fusion to T2 compared with T3/T4 lead to improved shoulder balance in adolescent idiopathic scoliosis with a double thoracic curve?

Proximal fusion level selection in adolescent idiopathic scoliosis (AIS) with a double thoracic curve (Lenke-2) remains debatable. The aim of this study was to compare the radiological outcomes of corrective surgery for Lenke-2 AIS according to the upper instrumented vertebra (UIV). This study included 74 patients who underwent corrective surgery for Lenke-2 AIS with the right main thoracic and left proximal thoracic (PT) curve at a single center. Various radiological parameters were measured using whole-spine standing radiographs preoperatively and postoperatively. Patients were grouped by proximal fusion level: T2 (group F; fusion, N=15) or T3/T4 (group NF; nonfusion, N=59). Preoperative and postoperative radiological parameters were compared between the two groups. Group NF was divided on the basis of the existence of a postoperative shoulder imbalance (PSI; >15 mm) and a subgroup analysis was carried out. PT curve correction rate (58.5 vs. 46.3%, P=0.005), right shoulder depression (4.3 vs. 10.3 mm, P=0.020), and proximal adjacent wedging (1.1 vs. 3.5°, P<0.001) were different between groups F and NF postoperatively. In the subgroup analysis, the Risser grade (3.9 vs. 2.8, P=0.009) and the main thoracic curve flexibility (53.5 vs. 42.6%, P=0.038) were different between the PSI positive and the PSI negative group when T3 or T4 was chosen as the UIV in Lenke-2 AIS. If T2 is selected as the UIV in patients with Lenke-2 AIS, more PT curve correction, less right shoulder depression, and less adjacent disc wedging can be anticipated. If T3 or T4 is chosen as the UIV, then right shoulder depression can be a problem postoperatively. Greater skeletal maturity and higher flexibility of the main thoracic curve might be preoperative risk factors for PSI. Thus, extension of the proximal fusion to T2 can be considered if the patient shows greater skeletal maturation and more flexible main thoracic curve to prevent PSI in Lenke-2 AIS with the right main thoracic and left PT curve.