Spatial Relations Between the Vertebral Body and the Thoracic Aorta in Idiopathic Scoliosis

Purpose: In case of anterior surgery for scoliosis, screw penetration to the contralateral cortex of the vertebral body is often recommended. The purpose of this study is to evaluate the spatial relations between the vertebral body and the thoracic aorta in patients with idiopathic scoliosis.

Materials and Methods: The subjects of the study were ten patients with idiopathic scoliosis (two males, eight females) whose age was 12 to 17 years. There were two King type I curves, two type II curves, three type III curves, one type IV curve, one type V curve, and one thoracolumber curve. Cobb angle of them was 52º to 77º. An average level of the apical vertebra of the right thoracic or right thoracolumber curve was T 9.6.The patients underwent CAT scan from T1 to the pelvis as part of their planned surgery. Slice interval was either 5 mm or 10 mm. On each image of the vertebral body, a line l that passed the anterior edge of the rib heads of both sides was drawn. The line l represented the virtual passage of the screw. A virtual entry point of the screw was defined as a point of intersection of the line l and the right side edge of the vertebral body. A line m that passed the virtual entry point and the center of the aorta was drawn. An angle œ between the line l and m was measured. "Cross" type relations were defined as the line l crossed the aorta: frequency of "cross" type relations were analyzed. "Cross and close" type relations were defined as the line l crossed the aorta and a distance between the vertebral body and the aorta measured along the line l was less than 2 mm: frequency of "cross and close" type relations were analyzed.

Results: The descending aorta was observed at the level of T4 or T5 and caudal to them. The angle œ was smaller at T6, T7, T8 and T9 levels. There were 44 levels of "cross" type relations in nine patients: "cross" type relations accounted for 83% of T6, T7, T8, and T9 levels. There were seven levels of "cross and close" type relations in five patients, four at T6, two at T7, and one at T8 level. Six out of these seven "cross and close" type relations were upper end vertebra of right thoracic curve or caudal adjacent vertebra to it.

Conclusion: When planning anterior surgery for right thoracic or thoracolumbar curves, surgeons should pay attention to the close relations between the vertebral body and the thoracic aorta.