Variations in the position of the aorta and vertebral safe zones in supine, prone, and lateral decubitus for adolescent idiopathic scoliosis

Analyze the modifications in the “safe zones” of T4–L4 vertebral bodies relative to aorta according to patient positioning, as well as in the relationship between the aorta and the vertebrae. Patients with adolescent idiopathic scoliosis who underwent surgical treatment during 2017 were included. Preoperative whole spine MRI in supine, prone, and LD positions was performed. The safe zone right (SZR) was defined as the angle formed between X-axis (0o) and a line connecting the origin and the edge of the aorta, and the safe zone left (SZL) was the angle between the edge of the aorta to 180o (X-axis). A total of 21 patients were studied, median age was 15.2 years, and 71.4% were female. The mean SZR lied from 0°–86.1o at T4 to 0°–76.9o at L4 in supine, from 0°–84.05o at T4 to 0o–78.5o at L4 in prone, and from 0° to 91.75o at T4 to 0°–80.4o at L4 in LD. While the mean SZL was located from 155.4o–180o at T4 to 107.9o–180o at L4 in supine, from 134°–180° at T4 to 103.9°–180° at L4 in prone, and from 143.8o–180o at T4 to 106o–180o at L4 in LD. Statistically significant differences were found almost at all levels when comparing supine versus prone and LD. Patient positioning during spinal surgery significantly modifies T4–L4 vertebral safe zones relative to aorta. These variations should be taken into account when analyzing an MRI performed in supine if the patient is undergoing surgery in a different position, to avoid vascular-related injuries.