Plasticity of vertebral wedge deformities in skeletally immature patients with adolescent idiopathic scoliosis after posterior corrective surgery

BACKGROUND: Vertebral bodies in patients with adolescent idiopathic scoliosis (AIS) usually have frontal wedge deformities. However, the plasticity of the deformed vertebrae in skeletally immature patients is unknown. The purpose of our study was to clarify the plasticity of vertebral deformities in skeletally immature patients with AIS by using in vivo three-dimensional (3D) analysis. METHODS: Ten female patients with AIS (mean age, 12.2 years; three patients, Lenke type 1; five patients, type 2; two patients, type 5) who underwent posterior fusion and whose Risser grade was ≤3 at surgery were included. Using computed tomography images (0.625-mm slice thickness) obtained 1 week and 1 year postoperatively, a total of seventy-three 3D bone models of vertebrae was made. The 3D bone models were made between the upper and lower end vertebrae within the main thoracic curve for patients with Lenke types 1 and 2 scoliosis, whereas they were made within the thoracolumbar/lumbar curve in patients with Lenke type 5 scoliosis. The height of the concave and convex sides in the anterior, middle and posterior parts of the vertebral bodies was measured using the original digital viewer, and the vertebral height ratio (VHR: concave/convex) was calculated. VHRs at 1 week and 1 year postoperatively were compared using the Wilcoxson signed-rank test. Differences were considered statistically significant at p < 0.05. RESULTS: VHR of the end vertebrae (n = 20) did not change postoperatively for any parts of the vertebral bodies. VHR of the vertebrae in the apical region (n = 28) also remained unchanged postoperatively. In contrast, VHR of the other vertebrae (n = 25) increased significantly in the anterior part postoperatively (from 0.938 to 0.961, p = 0.006). CONCLUSIONS: The wedge deformity of vertebral bodies showed a reshaping potential towards a symmetrical configuration in the region other than end and apex, although no plasticity of the vertebrae was observed in the apical region even in skeletally immature patients with AIS.