Segmental Characteristics of Main Thoracic Curves in Patients with Severe Adolescent Idiopathic Scoliosis

OBJECTIVE: Segmental flexibility in adolescent idiopathic scoliosis is crucial for the development of nonfusion and osteotomy technology. However, only global curve flexibility has been assessed in previous studies. Knowledge about segmental characteristics is absent. METHODS: Twenty patients with severe adolescent idiopathic scoliosis were enrolled in the present study. The vertebral and disc wedge angles were measured, and the segmental flexibility index was assessed by the correction rate of disc wedging on the traction film. Least significant difference analysis was used to compare the distribution of the variable. The patients were divided into 2 groups according to the stiffness of the global curves, and their relative wedging was compared. RESULTS: Vertebral wedging decreased from the apex toward the end. The apical and adjacent vertebrae accounted for 67.44% +/- 8.05% of the total vertebral wedging deformities. Disc wedging significantly decreased upward and downward from the apex. Disc wedging demonstrated no significant differences between U1 (first above the apex) and U2 or L1 (first below the apex) and L2, and these 4 discs accounted for 75.47% +/- 9.25% of the total disc wedging deformities. The levels close to the apical discs (U2 and L2) had the smallest extent of limited correctability. Segment disc flexibility showed a W-shaped distribution. The disc angle in the non-stiff group was significantly larger than the vertebral angle (40.13 degrees +/- 4.67 degrees vs. 26.62 degrees +/- 6.99 degrees; P< 0.001); however, similar results were not noted in the stiff group. CONCLUSIONS: Significant apical tethering in both vertebral body and disc wedging occurred, and the relative wedging changed significantly according to the rigidity of the main thoracic curves.