The Imaging Anatomy Study Of Sacral Nerve In The Sacral Neural Tube

Objedtive: The injury of posterior pelvic ring, such as sacral fracture,sacroiliac joint dislocation and sacroiliac joint fracture-dislocation, is a severeinjury with high incidence, whose treatment is an difficult problem whenorthopaedic surgeon faces. Insert the sacroiliac screw is the most popularmethod. However,because of the irregular shape of the sacrum,the complexstructure surrounding the sacroiliac joint and the limitations of the imageguiding device,the screw may easily damage the iliac vessels, lumbosacraltrunk, sacral nerve,cauda equina and so on,which will cause severecomplication. The sacral neural tube is a tube from intervertebral foramen toanterior sacral foramina of sacrum, it contains the anterior branch of sacralnerve. Denis Ⅱ type sacral fracture is the sacral fracture which fracture linespread to sacral foramina,on this occasion the fracture bone fragment canpenetrate the sacral neural tube,then the sacral nerve can be injured damageeasily.The misplacement of sacroiliac screw and Denis Ⅱ type sacral fracturealways lead to the sacroiliac screw and fracture bone fragment penetrate thesacral neural tube.In our clinic work, if such a case is encountered, we willremind ourselves the sacral nerve is injured or in high risk,then we have towithdraw the sacroiliac screw or take out the fracture bone fragment inoperation.Whereas,the patient whose sacroiliac screw do not withdraw orfracture bone fragment do not take out have no symptoms related to the sacralnerve injury.So,not all of the the sacroiliac screw and fracture bone fragmentpenetrating the sacral neural tube can damage the sacral nerve. Based on theabove analysis, We observe the anterior branch of sacral nerve in sacral neuraltube under the CT images,then we can firstly remember the exact position ofsacral nerve in every section of the sacral neural tube,secondly realize the ratio of sacral nerve area in every section of the sacral neural tube.That willsupply us with imaging anatomy knowledge to help us insert the sacroiliacscrew accurately and redefine the indications of operation of Denis Ⅱ typesacral fracture.Methods: All of30volunteers have a CT scan of sacrum. TheSIEMENS CT (SIEMENS company,Germany)is sixty-four detector row spiralCT.The condition of scanning:voltage120KV, electric current150MA,thickness5.0mm, matrix512×512.Then find out all of30volunteers‵s CTscan of sacrum in WORKSTATION of sixty-four detector row spiral CT.In theRecon window, post-thin-processing of all of30volunteers‵s CT scan ofsacrum according to the thickness1.0mm, softness B30f medium smooth,osteo window.In the3D window, choosing the Free Mode, adjusting the threered blue and green cross line orthogonality. Restructuring the images which isvertical to the superior border of S1vertebral body according to the thickness1.0mm, distance1.0mm.Then choosing the images into nextstage—measurement which can show the border of the sacral neural tube andthe sacral nerve clearly.Each volunteer has six images of S1neural tube andthree images of S2neural tube(each image consist of bilateral S1or S2neuraltube). Transferring all the clear images from the SIEMENS CTWORKSTATION to the PACS(Picture Archiving and CommunicationSystems). Measuring sacral neural tube and sacral nerve area in everysection, calculating the ratio of sacral nerve area in every section of the sacralneural tube. Then opening the images with Adobe Photoshop software.Findout the center of the sacral neural tube and sacral nerve A and B.Make acoordinate axis according to original point A, the per unit length of Y axis is1/2maximum length of the sacral neural tube, the per unit width of X axis is1/2maximum width of the sacral neural tube.Using the measurement functionof Adobe Photoshop software, calculate the exact coordinate（x,y） of thesacral nerve center.Results: The exact coordinate（x,y） of the sacral nerve center in everysection.The x and y follow the Gaussian distributions.We use the mean± standard deviation indicating the x and y of sample.Then conclude thecredibility interval of population mean according to the sample mean：left S1.1section﹝（0.11,0.13），（0.12,0.12）﹞、right S1.1section﹝（-0.22,-0.20），（0.11,0.11）﹞、left S1.2section﹝（0.13,0.14），（0.11,0.11）﹞、right S1.2section﹝（-0.25,-0.21），（0.09,0.11）﹞、left S1.3section﹝（0.14,0.16），（0.13,0.15）﹞、right S1.3section﹝（-0.23,-0.21），（0.12,0.14）﹞、left S1.4section﹝（0.10,0.12），（0.12,0.14）﹞、right S1.4section﹝（-0.26,-0.24），（0.12,0.12）﹞、left S1.5section﹝（0.15,0.16），（0.11,0.11）﹞、right S1.5section﹝（-0.20,-0.19），（0.10,0.10）﹞、left S1.6section﹝（0.12,0.14），（0.09,0.11）﹞、right S1.6section﹝（-0.22,-0.20），（0.09,0.09）﹞，left S2.1section﹝（-0.01,0.01），（0.19,0.21）﹞、right S2.1section﹝（0.01,0.01），（0.18,0.20）﹞、left S2.2section﹝（-0.02,-0.02），（0.17,0.17）﹞、rightS2.2section﹝（-0.02,0.00），（0.22,0.22）﹞、left S2.3section﹝（0.03,0.03），（0.20,0.22）﹞、right S2.3section﹝（0.01,0.01），（0.23,0.23）﹞。The ratio of sacral nerve area in every section of the sacral neural tubefollow the Gaussian distributions. We use the mean±standard deviationindicating the ratio of sample.Then conclude the credibility interval ofpopulation mean according to the sample mean：left S1.1section (0.46,0.49)、right S1.1section (0.34,0.36)、left S1.2section (0.54,0.56)、right S1.2section (0.55,0.59)、 left S1.3section (0.51,0.52)、 right S1.3section(0.51,0.54)、left S1.4section (0.45,0.48)、right S1.4section (0.37,0.40)、leftS1.5section (0.45,0.46)、right S1.5section (0.51,0.52)、left S1.6section(0.40,0.43)、right S1.6section (0.45,0.46)，left S2.1section (0.43,0.44)、rightS2.1section (0.35,0.40)、left S2.2section (0.51,0.54)、right S2.2section(0.46,0.49)、left S2.3section (0.44,0.45)、right S2.3section (0.36,0.37).Conclusion: We can observe the anterior branch of sacral nerve in sacralneural tube clearly under the CT images,then we can firstly remember theexact position of sacral nerve in every section of the sacral neural tube, thatwill supply us with imaging anatomy knowledge to help us insert thesacroiliac screw accurately;secondly realize the ratio of sacral nerve area inevery section of the sacral neural tube，that will help us to redefine the indications of operation of Denis Ⅱ typesacral fracture.