Study Of The Safe Application Of Pedicle Screw Bicortical Fixation In The Thoracolumbar Vertebrae

OBJECTIVE: How to improve the strength of pedicle screw fixation has always been the focus of spinal surgery research,especially the aggravation of population ageing,which makes the need to solve this problem more and more prominent.Pedicle screw bicortical fixation is a simple and effective method to enhance the strength of internal fixation,but it has not been widely promoted in clinic because of the risk of vascular injury.In order to control the risk of vascular injury,the Anatomic relationship between the thoracolumbar spine and the pre-vertebral great vessels was observed by CT three-dimensional reconstruction in prone position,to explore the safety methods of pedicle screw fixation with bicortical fixation.METHODS: Forty healthy adults,20 Male and 20 female,who volunteered to participate in the study were selected for three-dimensional CT examination of thoracolumbar segment(T9-L3)in prone position and supine position,respectively.For obtain clearer image,angiography was performed by injection of iodine contrast agent during the scanning process.The acquired images were reconstructed using the post-processing workstation of PHILIPS i CT image.The experiment was designed to obtain an axial image of the optimal pedicle screw trajectory plane,which was perpendicular to the posterior plane of the vertebral body.In order to facilitate observation and measurement,the reference line was marked as axis X,axis Y,and origin O.The X axis passed through the center of the pedicle,and the Y axis passed through the midline of the vertebral body.The angle of the Aorta and the inferior Vena Cava relative to the vertebral body was measured ?AOY/?VOY.The relative distance between the anterior great vessels and the vertebral body was measured in this direction,AVD / VVD.Self-controlled experiments were carried out in the prone and supine positions.The data obtained were analyzed using SPSS 22.0 statistical software.RESULTS: In prone position and supine position,the distance between aorta and vertebral body of T9~L3 segment decreased at first and then increased.In the prone position,the minimum AVD was at T12,which was 3.39±0.99 mm.The AVD increased more in the prone position than in the supine position,and the AVD values measured at the T9,T10,T 11,L2 vertebral bodies differed significantly between the prone and the supine positions(P < 0.05).The aorta of the T9-L3 segment tended to shift from the anterolateral side of the vertebral body to the anteromedial side.Except for T12 and L1,there were significant differences between the angles of AOY in the prone and the supine positions(P < 0.05).The prone position is closer to the midline of the spine than the supine position,in the range of 0°-30° near the midline.The vertebral bodies of T12 and L1 were relatively fixed with the aorta,AVD/?AOY were no significant difference in prone and supine position(P?0.05).In the prone and the supine positions,the distance between IVA and vertebral body of L1~L3 segment decreased gradually.However,the VVD values measured at the L1–L3 vertebral bodies didn't differ significantly between the prone and supine positions(P?0.05).the minimum VVD was at L3,which was 5.50±2.17 mm.However,it was limited to the 20°–30°position near the midline of the vertebral body.There was no significant difference in the values of ?VOY between prone position and supine position(P ? 0.05).CONCLUSION: The Aorta position in the T9-L3 vertebral body can be changed due to the change of body position.The aorta in prone is farther from the vertebral body and closer to the center.The inferior Vena Cava was relatively fixed in the anterior position of the L1-L3 vertebral body.It is safe to ensure that the protruding tips of the screw is less than 3mm in the treatment of thoracolumbar spinal diseases with pedicle screw bicortical anchorage.When judging the shortest distance,the measurement in the supine position is safer,but the prone position CT should be referred to when choosing the implantation direction TSA.Due to the mobility of the aorta in different postures and individual differences in anatomy,the prone position CT can help doctors to make better preoperative plans and decisions,which is of great significance for safe implementation of the bi-cortical fixation..