Change Of The Positions Of Aorta And Conus Medullaris In Ankylosing Spondylitis Patients With Thoracolumbar Kyphosis:a Magnetic Resonance Imaging Investigation

Part one:Does the Position of the Aorta Change with the Altered Body Position in Ankylosing Spondylitis Patients with Thoracolumbar Kyphosis?Objective:Aortic complications may occur during the lumbar spine osteotomy in correcting thoracolumbar kyphosis secondary to ankylosing spondylitis (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. And this study aims to quantitatively explore the differences in the anatomic position of the aorta relative to the spine between supine and prone positions in AS patients with thoracolumbar kyphosis.Methods:From 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 years) 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 (a) was set at 0.05.Results:At 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.Conclusions:There 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.Part two:Does the position of conus medullaris change with the increased thoracolumbar kyphosis in ankylosing spondylitis patients?Objective:One previous study revealed no significant change of conus locations in patients with idiopathic scoliosis; however, the effect of ankylosing spondylitis (AS)-related thoracolumbar kyphosis on conus position remains unexplored. In this study, we investigated the variation of conus medullaris terminations in patients with thoracolumbar kyphosis secondary to AS when compared with normal subjects, and evaluated the relationship between conus positions and the magnitude of kyphosis.Methods:MR images of 96 AS patients with thoracolumbar kyphosis, including 86 males and 10 females with an average of 34.6 years (range,17-65 years), and 100 age-matched normal controls were reviewed to determine the conus terminations in relation to spinal levels, which were assigned numerical values according to the standard method. Sagittal parameters of the AS group measured on radiograph included:global kyphosis (GK), thoracic kyphosis (TK), lumbar lordosis (LL). and thoracolumbar junction (TLJ).Results:There was no significant difference of the conus distributions between AS and control group (P=0.49), and conus tips located at the mean level of the lower third of L1 in both groups. In addition, conus medullaris displayed similar positions in AS patients among various apical region groups (P=0.88), and no significant difference was found when AS population was stratified into GK ranges of 30° (P=0.173). Also, no remarkable correlation of the conus positions with GK (r=-0.15. P=0.15), TK (r=-0.10. P=0.34). LL (r=-0.10, P=0.32), and TLJ (r=-0.06, P=0.54) was identified.Conclusions:The conus terminations displayed a wide range of distributions in AS patients with thoracolumbar kyphosis, which was similar to normal subjects. Moreover, the conus located at a relatively fixed position and would not be affected by the change of kyphosis magnitude.