| Objective: Percutaneous sacroiliac screw insertion, a better way for thestabilization of serious orthopedic injuries including sacroiliac jointdislocation, sacrum fracture and sacroiliac fracture-dislocation, has beenwidely used in clinical practice. Although C-arm X-ray assisted percutaneousinsertion, CT-assisted percutaneous insertion and computer-aided navigationfor percutaneous insertion are all feasible approaches for screw insertion, mostdoctors prone to use intraoperative C-arm X-ray assisted percutaneousinsertion, in favoring the fact that intraoperative screw positioning based oninlet, outlet and lateral fluoroscopic views is a better approach. However, dueto the complex anatomical structures around the sacroiliac joint, theirregularity and variability in sacrum anatomy, as well as the limitations inC-arm X-ray, it is very likely to injure important structures, including iliacvessels, lumbosacral trunk, sacral nerves and cauda equina that would causeserious complications. Fluoroscopic blind-area has been confirmed in the inletand outlet view positioning during the study of sacroiliac screw insertion onanterior superior area of sacral ala slope. But the specific size of the blind-areahas not yet been studied.In this study, the location and size of the blind-area were determinedusing CT scanning method, along with the proportion of the blind-area on theinlet and outlet views using X-ray fluoroscopy. A better way was proposed forsacroiliac screw insertion to avoid misplacement, reduce surgicalcomplications and to provide a more secure, convenient and reliable way forsacroiliac screw insertion under the guidance of C-arm X-ray technique.Method: CT scan images of108patients (excluding patients with sacrallesions and anatomical variation like fracture, rheumatism, tuberculosis,cancer, etc.) who received sacrum or sacroiliac joint scanning in the Third Hospital of Hebei Medical University during April to October2012, wereincluded in the study. There were in total56male patients and52femalepatients, aged24-64(mean age of44.11) in the study.SIEMENS64-slice spiral CT machine (SIEMENS, Germany) wasapplied in the study, scanning conditions: voltage120KV, current150MA,thickness5.0mm, matrix512×512. And syngo CT WORKSTATION wasused for data processing. For the reconstruction of1mm scanning image data,Recon function was used and the sagittal images of sacral were reconstructedin3D window with a layer thickness and distance of1mm; while themorphology of sacral ala slope could be observed in sagittal view. Thedirection perpendicular to the inspection station was set as0°. And threecontinuous layer images that go through the medial of uppermost anteriorsacral neural foramina were taken with "View" function; and the Distance toolwas used to draw a straight line parallel to the uppermost anterior sacralneural foramina, i.e. the direction of outlet view; and the angles of the3lineswas recorded and the average value was represented as θ. Then a lateralsagittal image of anterior sacral foramina S1was taken, and the Distance toolwas used to draw two straight parallel lines in the direction of outlet viewalong superior and inferior edge of S1, respectively; and the projection anglewas set as θ in the direction of outlet view. After that, the distance L4betweenthe two lines was measured using Distance tool along with the blind-arealength L3in the anterior superior area of sacral ala in the direction of outletview; the measuring directions of L3, L4were both perpendicular to thedirection of projection of outlet view; and a tangent was drawn to the anteriorborder of S1and S2, which is the direction of inlet view. The line was thencopied and moved to the posterior edge of S1, and the distance L2betweenthe two parallel lines was measured along with the length L1of the blind areain the anterior superior area of sacral ala in the direction of inlet view. Themeasuring directions of L1, L2were all perpendicular to the direction ofprojection of inlet view;The data was then input into Microsoft Excel to calculate L1/L2and L3/L4.Statistical analysis was performed using SPSS13.0software, and datawith normal distribution was represented as mean±SD. And two independentt-tests were performed for male patients and female patients respectively. Datawith skewed distribution was analyzed using rank sum test with α=0.05, andP<0.05was considered as significant.Results: The sagittal image of sacral ala slope was flat in the medial andconcaved in the anterior and posterior part. The concave in the anteriorsuperior part is the blind-area in fluoroscopy of the inlet and outlet views. Inthis study, CT images of108patients were included, in which56cases weremale patients with a mean age of42.95, and52cases were female patientswith a mean age of45.37. For the analysis of age difference between male andfemale patients, t-test was performed, and P>0.05was obtained, showing nosignificant difference. The mean values in age of the two groups werematching with each other. In the CT data of the56male patients, the resultsshowed that L1:1.074±0.189cm, L3:1.120±0.178cm, L1/L2:0.341±0.051,and L3/L4:0.394±0.042; the data in52female patients showed that: L1:1.028±0.162cm, L3:1.069±0.120cm, L1/L2:0.324±0.042, L3/L4:0.378±0.047. For the comparison between two groups, t-test was applied and nosignificance was found in the differences of L1, L3, L1/L2and L3/L4in twogroups.Statistical analysis was performed for all samples and the results showedthat: the length of blind-area L1in inlet view is1.052±0.177cm, which lieswithin95%medical reference range [0.704,1.399] cm; the length ofblind-area in outlet view L3is1.096±0.154cm, which lies within95%medical reference range [0.793,1.398] cm; and the proportion of blind-arealength to the thickness of sacral ala L1/L2is0.333±0.047in inlet view, whichis about1/3and lies within95%medical reference range [0.240,0.426]; andthe proportion of blind-area length to the height of S1L3/L4in outlet view is0.386±0.045, about2/5, and lies within95%medical reference range[0.298,0.474]. Conclusion: The sagittal image of sacral ala slope was flat in the medialand concaved in the superior and inferior part. The concave in the anteriorsuperior part is the blind-area in fluoroscopy of the inlet and outlet views. Themedical reference range of the blind-area in inlet view is [1.399±0.704] cm,while the value in outlet view is [0.793,1.398] cm. The proportion of theblind-area length to the thickness of sacral ala was about1/3, and theproportion of the blind-area length to the height of S1is about2/5. So, if thescrew was found to be located within1/3of the anterior sacral ala in the inletview, and within2/5of the superior S1, the screw had probably perforatedthrough the cortex of the anterior superior part of sacral ala slope and enteredthe blind-area. If the screw entered the blind-area, it could be adjusted to aposterior and inferior direction (increase L1and L3) or use a shorter screw. |
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