| Computed tomography (CT) with multiplanar reconstruction (MPR) evaluation of sacrum and L5 vertebra was performed to demonstrate the feasibility and security for safe placement of longitudinal lumbosacral cannulated screws.Summary of background dataThe ideal fixation for Lumbosacral dislocation has been problematic and controversial with a variety of techniques. We treated Lumbosacral dislocation by a special fixation procedure with lumbosacral pedicle screws combinding 2 cannulated screws which were longitudinal inserted through lateral mass of the sacrum, sacral body, L5S, disc to L5 vertebral body. The morphometric study of the sacrum related to this procedure need to be performed in detail.MethodsPart I15 dry sacra with vertebra were obtained for computed tomography (CT) e-valuation. CT scans was performed using a Marconi MX8000 machine (Philips) in the Department of Radiology. Sequential 3. 2-mm continuous cross-sectional images were made parallel to both upper and lower endplates for L5 vertebra and the upper sacrum. From the series of images, the image of sacral mass with the smallest cross-sectional area was magnified. The cortical margins of the sacral mass at its most narrow portion were circumscribed on the computer. The dimensions of the sacral mass (including height, width, and area) through the geo-metric center of this narrow portion were then measured by computer.Then, multiplanar reconstruction ( MPR) was performed to determine the i-deal sagittal angle of the screw passage, and the oblique plane of the screw trajectory was created under the ideal sagittal angle. At just plane of screw trajectory, the simulated screws were inserted through the lateral mass of the sacrum, sacral body, L5S1 disc to L5 body. The ideal angles on sagittal and coronal plane, and ideal length of the srews were measured. According to above average results, screws were inserted to sacral specimens, and X-ray plain films were performed to prove whether the CT evaluation was reliable to guid longitudinal placement of lumbosacral cannulated screws.Part II31 patients' CT images from the Picture Archiving Communication System (PACS) were elected, who were present with low back pain to the orthopaedic spinal clinic at the second hospital of China Medical University between Aug 2002 and Oct 2003. There were 14 male patients and 17 female patients, mean age 34.5 + 14.2 with an age range of 17-68 years. Patients with vertebral body abnormalities, gross spinal pathology (including spondylolisthesis, retrolisthe-sis, disc space collapse) and those who had undergone spinal surgery were excluded. With CT multiplanar reconstruction and surgical simulation in the workstation like that of part I , bony sacral mass geometry and safe passage of lumbosacral screws including the ideal angles on coronal and sagittal plane, optimal length of the screws, the limit angles and the limits of the safe insertion area were determined.A statistical analysis was performed using the SPSS11.0 software. A t-test for dependent samples was used to compare the data between male and female, symmetric structures, and dry sacra group and patients group. A significance level of P < 0.05 was used.ResultsThe narrowest portion of the sacral mass in both groups was consistently located at the level of S1 foramen. The average height at the geometric center in cross-section of the bony sacral mass at the first sacral foramen was 35.54 +4. 07mm and 36. 73 +5. 33mm, the average width was 21.60 +3.39mm and 21. 71 +3. 18mm, and the smallest area was 6.09 + 1.22cm and 6.21 + 1.05cm in 15 dry sacra and 31 patients images, respectively. No difference was present between dry sacra group and patients group (P>0.05). Though the variability of the sacral geometry was present, there was ample cross-sectional area to accommodate the lumbosacral cannulated screws if correctly positioned.In dry sacra group, the ideal angles of the screw passage in coronal and sagittal plane were 65.4 +2.7 and 27.7 +2.9 respectively. The average optimal len... |
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