The position of the spinal cord relative to the vertebrae in adolescent idiopathic scoliosis

We aimed to clarify the position of the spinal cord relative to the vertebra in patients with Lenke type 1 adolescent idiopathic scoliosis (AIS). In all, 35 patients with Lenke type 1 AIS who underwent posterior spinal fusion using a pedicle screw construct and preoperative computed tomography (CT) after myelography were recruited. The following radiological parameters were measured on preoperative CT myelography: spinal cord–vertebral (SV) angle, entry–spinal cord distance (ESD), ESD-X, ESD-Y, spinal cord–pedicle (SP) angle, and rotation angle (RAsag). The SV and SP angles were the smallest at T9 level, followed by T8 and T7 levels, and tended to increase cranially and caudally. The ESD was the shortest at T9 level, followed by T8 and T10 levels. The ESD-X was the smallest at T9 level, followed by T8 level, while the ESD-Y was the smallest at T10 level, followed by T9 and T8 levels. Mean RAsag increased from T4 to T9 levels and decreased from T9 to T12 levels. The ESD was significantly negatively correlated to RAsag. Among all apical vertebrae, the SV and SP angles were negatively correlated to Cobb angle. The RAsag was positively correlated while the ESD was negatively correlated to the Cobb angle. The spinal cord is close to the vertebrae in the apical vertebral region and far from the vertebrae at the upper and lower thoracic vertebral levels in AIS. Therefore, the potential risk of spinal cord injury by pedicle screw is the highest in the apical vertebral region.