Morphometrric Analysis Of Retroperitoneal Vessels And Nerves With Respect To Lateral Lumbar Interbody Fusion And Approach-related Complications Avoidance

Part I The morphometric study for safe zone and psoas injury with respect to lateral lumbar interbody fusionObjective:To identify the relative position of lumbar plexus,genitofemoral nerve and major vessels to determine the safe zone from L1-L2 to L4-L5.Methods:70 patients who had consecutive lumbosacral spine MRI scans between February,2013 and January,2017 were retrospectively reviewed.The relative position among lumbar plexus,genitofemoral nerve and major vessels was measured in axial images and the potential psoas injury at different corridor sizes,corridor slopes and entry points was also analyzed using cross-sectional area(CSA)method.Results:The anteroposterior distance between lumbar plexus and major vessels was largest at L1-L2(29.8mm)and smallest at L4-L5(22.9mm).The mean anteroposterior distance of lumbar plexus and genitofemoral nerve ranged from 12.7 to 14.9mm.While the mean distance for genitofemoral nerve and major vessels ranged from 7.1 to 13.8mm.A posteriorly located entry point,larger corridor size and corridor slope was associated with greater psoas injury.Conclusion:The safe zone was significantly narrowed at L4-L5,especially in female.It should also be noted that the safe zone in Chinese patients was generally narrowed comparing to westerns.Surgeons should be aware of this anatomic difference and choose appropriate surgical technique in our population.Besides,the genitofemoral nerve could be easily injured,which should be paid more attention during surgery.Part ? Access angle will change the risk of approach-related complications in lateral lumbar interbody fusionObjective:To investigate the potential risk of ipsilateral or contralateral neurovascular structure injury at different access angles.Methods:86 axial magnetic resonance images were obtained to analyze the potential risk of approach-related complications.The access corridor were simulated at different access angles and the potential risk of neurovascular structure injury was evaluated when the access corridor touching or overlapping the corresponding structures at each angle.Furthermore,the safe corridor length was measured when the corridor width was 18mm and 22mm.Results:When the access angle was 0°,the potential risk of ipsilateral nerve roots injury was 54.7%at L4-L5.When the access angle increased to 15°,the potential risk of injury to genitofemoral nerve was 94.2%,while the risk of contralateral nerve root injury was 17.4%.When access angle was 45°,the potential risk of abdominal aorta,contralateral nerve roots or central canal injury at L4-L5 was 79.1%,74.4%and 30.2%,respectively.The length of the 18mm-wide access corridor was largest at 0° and it could reach 44.5mm at L3-L4 and 46.4mm at L4-L5.While the length decreased to 34.5mm at L3-L4 and 36.2mm at L4-L5 at the angle of 45°.Conclusion:Changes in the access angle would not only affect the ipsilateral neurovascular structures,but also might adversely influence the contralateral neural elements.An excessively small access angle would increase the risk of ipsilateral nerve root injury,while a large angle posed high risk to abdominal aorta as well as the contralateral nerve roots or even central canal.We recommended that the access angle between 5° and 15°was safe and feasible for lateral lumbar interbody fusion as the risk of neurovascular injury reduced when using this angle and the safe length was long enough to implant a large cage.Part III Positional alteration of retroperitoneal vessels and nerves in adult degenerative scoliosis and its implication to lateral approachObjective:To investigate the position of retroperitoneal vessels and ventral nerves in adult degenerative scoliosis and then,analyzing the correlation between radiographic parameters and position of these neurovascular structures.Methods:A total of 208 cases were retrospectively reviewed between April 2012 and December 2017.These cases were divided into 3 groups:group 1 consisted of patients with degenerative scoliosis,which were further divided into right or left convexity;group 2 consisted of degenerative but normally aligned segments;group 3 consisted of patients with degenerative scoliosis and were treated with XLIF procedure.The distance between nerve roots or major vessels and disc center was measured to identify the positional alteration in scoliosis.Furthermore,the distance between nerve roots or major vessels and S1 center was also measured to determine the shift of these neurovascular structures after surgery.Finally,the correlation analysis was employed to determine the relationships between the position of these neurovascular structures and radiographic parameters in scoliosis patients.Results:In left-side curve,the distance between left nerve root and the disc center in scoliosis was significantly larger than patients without scoliosis from L1-L2 to L3-L4(p<0.001).While the distance between right nerve root and the disc center in scoliosis was significantly smaller(p<0.05).In all patients with scoliosis,the safe zone in convex side was significantly larger(p<0.05).Correlation analysis showed that Cobb angle and vertebral rotation was correlated with the difference between the position of left and right nerve roots(p<0.05).While vertebral rotation and LL was correlated with the position of the venae cava(p<0.05).Conclusion:In adult degenerative scoliosis,the nerve roots in convex side were positioned more posteriorly,whereas major vessels lacked significant positional differences between concave and convex side.Therefore,the safe zone in convex side was significantly larger and approaching the curve from convex side could reduce the risk of approach-related complications.Besides,Cobb angle as well as the vertebral rotations will significantly affect the position of nerve roots and major vessels.Surgeons should make careful examination prior to surgery when the patient had larger Cobb angle or vertebral rotations.