Rule breakers achieve successful shoulder balance: unraveling the myth of upper instrumented vertebrae selection criteria

This study compared shoulder balance outcomes in "rule breakers" (RB) vs. "rule followers" (RF) based on commonly utilized upper instrumented vertebrae (UIV) selection guidelines. Adolescent idiopathic scoliosis (AIS) patients (Lenke 1-4) who underwent posterior spine fusion (PSF) with minimum 2-year follow-up had radiographic measurement of shoulder balance including first rib angle (FRA), T1 tilt, coracoid process height difference (CPHD), and clavicle angle (CA) at preop, postop, 6-month, 1-year, and 2-year timepoints. Postoperative outcomes were compared between RB and RF groups defined based on the UIV selection guidelines of Rose and Lenke. Among 88 patients (43 RF, 45 RB), age, gender, preoperative T1 tilt, FRA, CA, and CPHD were not significantly different between groups (p > 0.05). Immediately post-surgery, the RF group had more balanced shoulders (CPHD: 11.6 mm vs. 15.7 mm, p = 0.033; CA: 2.8° vs. 3.6°, p = 0.045; FRA: 3.4° vs. 5.1°, p = 0.009; T1 tilt: 4.7° vs. 6.1°, p = 0.045). At 2 years, no difference was observed between RF vs. RB in CA (2.3 vs. 2.2°, p = 0.857) and CPHD (8.5 vs. 8.1 mm, p = 0.791). FRA and T1 tilt were higher in RB vs. RF (FRA: 4.6 vs. 2.9°, p = 0.002; T1 tilt: 5.6 vs. 3.9, p = 0.008). Shoulder balance (CPHD