• Zhe Qu, Qian Bang-Ping, Yong Qiu, Ben-Long Shi, Ming-Liang Ji, Bin Wang, Yang Yu, and Ze-Zhang Zhu.
• The Department of Spine Surgery, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China.
• J Spinal Disord Tech. 2015 Jun 18.

Study DesignA prospective magnetic resonance imaging (MRI) study.ObjectiveTo quantitatively explore the differences in the anatomic position of the aorta relative to the spine between supine and prone positions in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis.Summary Of Background DataAortic complications may occur during the lumbar spine osteotomy in correcting thoracolumbar kyphosis secondary to AS, and a clear understanding of the spatial relationship between the aorta and the vertebrae is essential to prevent these iatrogenic complications. However, previous anatomical study was performed with AS patients in the supine position, which was different from the prone position adopted in surgery. To date, no report has been published to investigate the mobility of the aorta relative to the vertebrae between supine and prone positions in AS patients with thoracolumbar kyphosis.MethodsFrom March 2013 to September 2014, twenty-two AS patients (21 males, 1 female) with thoracolumbar kyphosis with a mean age of 30.7 years (range, 19-46▒y) were recruited. MRI examinations from T9 to L3 in both the supine and prone positions were performed, and the left pedicle-aorta (LtP-Ao) angle and LtP-Ao distance were measured at each level. The differences of these parameters between the two positions were compared by the paired Sample t-test, and the relationships between the shifting of the aorta and the change of global kyphosis (GK) and lumbar lordosis (LL) were evaluated by the Pearson correlation coefficient. The level of significance (α) was set at 0.05.ResultsAt T9-L3 levels, no significant difference was noted in LtP-Ao distances (43.78▒mm vs. 44.42▒mm; P=0.077) and LtP-Ao angles (0.82°vs. 0.22°; P=0.053) between supine and prone positions. The correlation analysis also revealed no remarkable correlation between the change of LtP-Ao angle and increase of global kyphosis (GK) and lumbar lordosis (LL) in the prone position.ConclusionsThere is no significant change of the relative positions between the aorta and the vertebrae at T9-L3 levels after the patient turned to a prone position, which implied that the mobility and range of motion of the aorta is limited in advanced stage of AS.

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