Positional changes on MRI of aorta relative to vertebra in different postures for ankylosing spondylitis patients with thoracolumbar kyphosis

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Aortic position  Magnetic resonance imaging

English Abstract:

  【Abstract】 Objectives: To investigate the anatomical relationships of aorta relative to spine in different postures(supine and lateral positions) for ankylosing spondylitis(AS) patients with thoracolumbar kyphosis based on magnetic resonance images(MRI). Methods: 33 AS patients with thoracolumbar kyphosis undergone single-level pedicle subtraction osteotomy(PSO) from May 2020 to December 2022 were included in the study. There were 29 males and 4 females, and the patients averaged 38.3±8.8 years old(22-54 years). Baseline information including age, gender, and apical vertebra was recorded. Global kyphosis(GK) was measured on lateral full-length spinal radiographs preoperatively. MRI examinations in supine and right or left lateral positions were performed in all patients preoperatively, and parameters including aorta-vertebra angle(θ), aorta-vertebra distance(d1), and the interval between posterior aorta wall to anterior vertebral cortex(d2) were measured. In order to analyze the influence of right and left lateral posture on the position of the aorta relative to the vertebra, patients were categorized into right and left lateral position groups according to the corresponding lateral positional MRI examinations performed preoperatively for comparing the aortic position relative to vertebra between supine posture and (left or right) lateral posture in both groups. All the patients were divided into mild(GK≤70°) and severe(GK>70°) kyphotic groups for analyzing the impact of the kyphotic degree on the aortic position; meanwhile, the difference of the position of aorta relative to vertebra between supine and (left or right) lateral postures were also explored according to varied degrees of kyphotic groups. Results: Of all the 33 patients, 22 were divided into the left lateral position group and 11 were in the right lateral position group. There was no significant difference of baseline information and GK between both groups. Except for d2 in right lateral position group at T12(P=0.033), no significant difference of θ, d1, and d2 between supine and lateral postures of both groups was observed at T9-L3; Moreover, no statistical difference was there in θ, d1, and d2 between supine and lateral postures of both mild kyphotic group and severe kyphotic group at T9-L3. At T9-T12, GK was significantly negatively correlated with θ(P<0.05); At T9, T10, and T12, GK was significantly positively correlated with d1(P<0.05). At T9-T11, smaller θ was noted in severe kyphotic group(T9-T10, P＜0.05; T11, P＝0.057); At T9, T10, and T12, larger d1 was observed in severe kyphotic group(P＜0.05); And at L1-L3, no significant difference of θ and d1 was found between mild and severe kyphotic groups. Conclusions: MRI in lateral position can be considered as a replacement of supine positional MRI for AS patients with severe thoracolumbar kyphosis before operation; During the procedure of osteotomy or pedicle screw insertion, the risk of aortic damage in lumbar spine might be larger than that in thoracic spine; The mobility of aorta and the position of aorta relative to vertebra in thoracic region is going to be impacted by the severity of kyphosis.