Impact of Sagittal Reference Lines on Predicting Distal Junctional Kyphosis in Adolescent Idiopathic Scoliosis

Incorporating the sagittal stable vertebra (SSV) in posterior spinal fusion (PSF) may reduce postoperative distal junctional kyphosis (DJK) in adolescent idiopathic scoliosis (AIS), but its determination varies across reference methods and may be affected by patient posture. This study aims to investigate the SSV determined by different sagittal reference lines in predicting the risk of DJK after PSF in AIS patients.

This retrospective cohort study evaluated AIS patients with Lenke Type 1 or 2 curves treated with PSF between January 2009 and July 2017. The inclusion or exclusion of SSV in PSF based on SSV determined by different reference lines was assessed for its association with the postoperative DJK. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and odds ratio were calculated.

One hundred twenty-two patients (mean age at surgery: 15.1 ± 3.2 years) were included with the incidence of postoperative DJK 6.6%. PSF with the exclusion of SSV, defined by the vertebral level at which 50% of the vertebral body was anterior to the posterior sacral vertical line (PSVL), the midline between PSVL and the C7 plumb line (PSVL-C7PL Midline), and the line connecting the center point of the C7 vertebral body and the posterior superior corner of the sacrum (C7PSL), was significantly associated with the occurrence of postoperative DJK. Among the evaluated reference lines, PSVL demonstrated numerically higher sensitivity, NPV, odds ratio, and area under the curve (AUC), although these differences in AUC did not reach statistical significance.

Although there are concerns about whether standing posture affects the SSV determined by a specific reference line, this study demonstrates that PSVL might be an effective and convenient reference line for identifying SSV.