Correlation Study Of Optimal Inversion Angle And Length In Lumbar Pedicle Screw Fixation

Background:Lumbar pedicle screw fixation is a routine surgical method for the treatment of lumbar diseases.The pedicle screw fixation system has been used as the gold standard for lumbar fusion due to its biomechanical advantages,but if the pedicle screws are placed improperly,complications such as nerve injury,vascular injury,pedicle rupture,and spinal cord injury will occur.Among them,the retroperitoneal large vessel injury was one of the most serious complications of this operation.Therefore,how to avoid such complications has been particularly important for spine surgeons.The factors that lead to the injury of prevertebral great vessels（PGVs）during pedicle screw placement include:anatomical variation of PGVs,abdominal surgery history,patient’s position during surgery,damage to annulus fibrosus and anterior longitudinal ligament,the length of the pedicle screw was too long,and the angle of the pedicle screw into the needle is bad,etc.However,the anatomical variation of PGVs,the history of abdominal surgery,the patient’s intraoperative position and the integrity of the preoperative anterior longitudinal ligament were factors that cannot be changed.Therefore,mastering the safe screw insertion angle and screw insertion length of pedicle screws was an effective method to reduce PGVs damage.At present,there are many studies on the position relationship between PGVs and vertebral bodies at home and abroad.However,few studies have focused on the risk of injury to PGVs at the pre-extrusion position of the pedicle screw at different inclination angles.And there were few studies on the optimal insertion depth of pedicle screws at different inclination angles to avoid vascular injury.Objective:To analyze the correlation between pedicle screw inclination angle and screw length,and to discuss the optimal inclination angle and screw insertion depth of the pedicle screw to reduce the incidence of PGVs injury.Methods:1)A coordinate system was established on the CT images of 110 patients with lumbar disc herniation（LDH）to simulate the trajectory of pedicle screws and the parameters were measured.2)Establishment of the coordinate system:select the lower outer corner of the superior articular process（the neck of the superior articular process）as the nail entry point O,and define the line connecting the needle entry points O on the left and right sides as the X axis,which will pass through point O.And the line perpendicular to the X-axis is defined as the Y-axis（Vertebral Sagittal）.The included angle between the pedicle screw trajectory and the Y axis is the inclination angle.3)Measuring methods and parameters:the left and right sides of L1-S1 were measured at different introversion angles（L1-L5:5°,10°,15°,S1:0°、5°、10°、15°）.According to D_AVC-PGV value（3 mm）,D_AVC-PGV was divided into four grades（I,II,III,N）,D_AVC-PGV≤3 mm was defined as grade III,3 mm<D_AVC-PGV≤5 mm defined as grade II,D_AVC-PGV>5 mm was defined as grade I,not touching blood vessels was defined as grade N.Then the distance between the O points with the AVC(D_O-AVC)was measured,and the average distance of the D_O-AVC was calculated.Finally,the distance between the O points with the PGVs(D_O-PGVs)was measured.Results:1)Under the different introversion angles of L1-S1,the best introversion angles on the left and right sides of L1-L3 were 5°,the best inclination angle on the left side of L4was 5°,on the right side was 15°.The best inclination angle on the left side of L5 was 5°,on the right side was 10°.The best introversion angle on the left and right sides of S1 was 15°.2)At L1-L3,when the inclination angle is 5°,the length of D_O-PGVS is greater than 55 mm.Therefore,when the screw length is controlled within 50 mm,the risk of screw damage to the PGVs can be reduced.At L4,when the screw length is controlled within 50 mm,the risk of screw damage to the PGVs can be reduced.At L5,when the inclination angle is 5°,the length of D_O-PGVS is greater than 50 mm.Therefore,when the screw length is controlled within 45 mm,the risk of screw damage to the PGVs can be reduced.At S1,when the inclination angle is 0°-5°,when the screw length is controlled within 40 mm,the risk of screw damage to the PGVs can be reduced,when the inclination angle is 10°-15°,when the screw length is controlled within 45 mm,the risk of screw damage to the PGVs can be reduced.Conclusion:1)The best introversion angles on the left and right sides of L1-L3 were 5°,the best inclination angle on the left side of L4 was 5°,on the right side was 15°.The best inclination angle on the left side of L5 was 5°,on the right side was 10°.The best introversion angle on the left and right sides of S1 was 15°.2)At the best inclination angle,the average length of the best pedicle screws in L1-L4 was 50 mm,the average length of the best pedicle screws in L5 was 45 mm.At S1,when the inversion angle was 0°-5°,the optimal average screw length was 40 mm;when the inversion angle was 10°-15°,the optimal pedicle screw average length was 45 mm.