Variations of Radiographic Parameters Relevant to the Presumed Lower Instrumented Vertebrae During Intraoperative Fluoroscopic Positioning for Lenke 5/6 Adolescent Idiopathic Scoliosis.

Background: Radiographic evaluation of the presumed lower instrumented vertebrae (LIV) is crucial for determining the optimal fusion level for adolescent idiopathic scoliosis (AIS) with main thoracolumbar/lumbar curves. However, few studies have examined its variations intraoperatively. This study aims to investigate the radiographic variations of the presumed LIV during fluoroscopic positioning to aid surgeons in decision-making.

Methods: Lenke 5/6 AIS patients who underwent correction surgery in our center were consecutively recruited from January 2021 to December 2023. The spinal radiographs, including preoperative standing X-ray, recumbent computed tomography (CT), and intraoperative positioning fluoroscopy, were collected. The parameters of the presumed LIV were measured and compared. The correlation analysis was also performed to establish the liner regression equation.

Results: Ninety-seven patients, comprising 23 boys and 74 girls, were enrolled, with an average main curve of 55.1 ± 11.0°. The vertebral body tilt and disc angle of the presumed LIV were 27.2 ± 6.2° and 8.5 ± 3.8° on preoperative standing X-rays, respectively, both significantly decreasing on CT images and intraoperative fluoroscopy. The rotation of the presumed LIV also showed significant differences intraoperatively. Significant correlations were observed between vertebral body tilt and disc angle across X-rays, CT images, and fluoroscopy. A linear equation was established for predicting intraoperative variations of the presumed LIV based on baseline X-rays.

Conclusions: This study firstly reports the radiographic variations of the presumed LIV using intraoperative positioning fluoroscopy for Lenke 5/6 AIS and establishes the correlation with baseline measurements. This information may assist surgeons in selecting the optimal LIV, but long-term follow-up is needed to evaluate its outcomes.