CT-based Radiographic Measurement Of The Approach Of Percutaneous Transforaminal Endoscopic Lumbar Interbody Fusion

Objective: A radiographic study was designed to measure the relationship between the exiting nerve root and its surroundings to their corresponding intervertebral disc for percutaneous transforaminal endoscopic lumbar interbody fusion procedure in order to better understand regional anatomy and better application in clinical.Methods: A retrospective study from January 2017 to October 2017 in Tianjin Hospital was carried out.The CT images was obtained from patients presented with low back pain.Those with scoliosis,lumbosacral transitional vertebrae,spinal injuries,tumors,tuberculosis,spondylolisthesis,herniated or collapsed intervertebral disc and previous spinal surgery were omitted from the study.The CT analysis was done bilaterally from L2-L3 to L5-S1.On the vertical plane of long-axis of pedicle which exiting nerve root is visible,nerve root-dural sac distance at the superior and inferior margin of the disc(Js?Ji),nerve root-pedicle distance at the medial,middle and lateral borders of the pedicle(Pa?Pb?Pc),pedicle width(W)and safe working zone which is the trapezoid bounded by the inferior pedicle and the exiting nerve root(S)were analyzed.On transverse plane,nerve root-articular process and nerve root-articular process joint surface shortest distance were analyzed at the superior and inferior margin of the disc(Gs?Gi)respectively.All radiologic measurements were obtained independently by two experienced radiologists.Intraclass correlation coefficient(ICC)was used for the reliability of measured data.All data were evaluated with digital analysis software SPSS 20.0(IBM,USA).Calculating the mean and standard deviation,the groups were analyzed using ANOVA analysis,and paired t-tests were used to compare the left and right sides.The P value < 0.05 was considered statistically significant.Result: 1.110 CT datum were collected,including 49 males and 61 females.The age ranged from 20 to 79 years and the mean age was(45.6±16.0)years.ICC was 0.796 to 0.916,indicating good consistency of measurement parameters.2.From L2-L3 to L5-S1,the distance of nerve root-dural sac was larger at inferior margin of the disc.And from L2-L3 to L5-S1,each segment of vertebral nerve root-pedicle distance was gradually reduced from medial to lateral;From L2-L3 to L5-S1,the distance from exiting nerve root to the middle and lateral edge of the pedicle gradually decreased,with the L5-S1 being the minimum.There were some statistical differences in the left and right sides of the L4-L5 and L5-S1.The pedicle width of the vertebral body gradually increased from L2-L3 to L5-S1.From L2-L3 to L5-S1,the mean area for the safe working zone was gradually increasing.3.In the axial plane,the shortest distance of nerve root-articular process joint surface at inferior margin of disc was larger than the distance of nerve root-articular process at superior margin of the disc from L2-L3 to L5-S1.There was no statistical different between the left and right sides.Conclusions: CT-based distance of exiting nerve root-its surroundings and area of safe working zone to their corresponding intervertebral disc could provide a reference about the size of cage for percutaneous transforaminal endoscopic lumbar interbody fusion.It is more difficult to implant a cage with a width of 10 mm above L3/4 segment.And removing the parts of superior articular process,it could expand the safe working area,and avoid hurting nerve or other structures for implanting a cage.A familiar with the three-dimensional anatomy of the spine and a better understanding of surroundings to exiting nerve root were fundamental for utilizing percutaneous transforaminal endoscopic lumbar interbody fusion safely and effectively.