| BackgroundThe lumbosacral region is important to maintain the stability of the spine and pelvis.The infection, tuberculosis, tumor, trauma and other diseases can lead the destruction of the intervertebral disc and vertebral body course the instability of the lumbosacral region.Because of the complex anatomy and special biomechanical characteristics of the lumbarsacral region, the surgical management to reconstruct the stability in this area is very challenging.There are a lot of surgical techniques for lumbosacral stability reconstruction, which can be divided into anterior column support procedures and posterior stabilization techniques. The anterior column support procedures include cage, the cage with screw, the cage and the plate, the axial lumbar interbody fusion and so on. Posterior stabilization procedures also have a variety of options, the S1 bicortical and tricortical pedicle screws, S2 pedicle screws, S2 alar screws, sacroiliac screws, Galveston technique, iliac screws and the sacral 2 alar iliac screws and so on. For the destruction of sacrum in severe cases, the S1 pedicle screw can’t be effect placed if the sacral 1 vertebral body was destroyed, in this time the lumbosacral pelvic fixation should beconsidered. Many spine surgeons have used iliac screws to achieve lumbosacral pelvic fixation in the sacral tumor resection, lumbosacral tuberculosis, lumbosacral traumatic instability because iliac screws procedure is simple and has high strength and achieved good clinical effect, but iliac screws breakage, loosening,pseudarthrosis are still not rare, especially in large range of lesion cases.So how to improve the reconstruction procedures in lumbosacral region, reduce the stress of the internal fixation system and how to choose the effective procedure in the different defects of lumbosacral regionis need more deeply research.We carry out the finite element analysis and the biomechanical test to study the biomechanical characteristic of the lumbosacral region and evaluate the stability of the different reconstruction procedures for clinical selection.Objective1. To establish a three-dimensional finite element model of normal adult L2-pelvis based on computed tomography scan data and verify its effectiveness.2. To establish a three-dimensional finite element model has the defect of the lumbar sacral region.2 kinds of reconstruction procedures were simulated in this model. The stability of the model and the stress of the internal fixation system were analyzed.3. A biomechanical test was performed on ovine lumbopelvis segment specimens to evaluate the stability of different lumbosacral reconstruction procedures after different resection of lumbosacral region.Methods1. Using 64 slice spiral CT scan a 24 year old male volunteer from L1 to pelvis get 577 images. The scan data was exported in the DICOM format and imported into the Mimics15.0 software. Using the"Draw Profile Line", "Thresholding", and "Region growing" and "Edit masks" function then generated a 3D surface model. The 3D solid model was establishedusing the SolidWorks software. The 3D solid model divided into mesh model by using the HyperMesh software. The model was given the material properties and analyzed by using the ABAQUS software. Constrained the roof of double acetabulum, applied a vertical load of 1000N, calculate the axial compression stiffness and stress distribution; applied the torque load of 7N.M in flexion, extension, left and right lateral flexion, left and right rotation calculate the torque stiffness and stress distribution then compared with other studies verify its effectiveness.2. The solid geometry model of the L3,4 pedicle screws combined with single iliac screwfixation and L3,4 pedicle screws combined with dual iliac screws and anterior titanium mesh cage support fixation were constructed by the Solidworks2012 software.The date of the 3D solid model from L2 to pelvis was imported into the HyperMesh software. We simulate the situation of defect of the lumbar sacral region; the defect range is from the lower of L5 pedicle to upper of S1 pedicle including the front part of the L5 and S1 vertebral body and the bilateral articular process.2 kinds of reconstruction procedures simulated above were used to reconstruct the stability of the lumbosacral region.The models were given the material properties and analyzed by using the ABAQUS software like step1.3.12 adult male ovine lumbopelvis segment fresh specimens (from L3 to pelvis). Using posterior spinal fixation system. L4-L5, S1 pedicle screw fixation was defined as the intact group(Group1). Group 2(S1 pedicle screw group) the specimen was resect the intervertebral disc of L6-S1 and the bilateral articular process and fixed with L4,5, S1 pedicle screw rod system. Group3 (Single iliac screw group) the specimens was resect the bilateral articular process and the lower of 1/2 L6 vertebral body and upper of 1/2 S1 vertebral body fixed with L4,5 pedicle screw, single iliac screw rod system. Group4 (Dual iliac screw group) the specimen in this group like group 3 but fixed with L4,5 pedicle screw and double iliac screw rod system. Group5 (Dual iliac screw+titanium mesh cage group) the specimen in this group like group 4 but add the intervertebral double titanium cage fixation. Biomechanical testing was applied 0-250N axial compression load and -5N.m ～5 N.m axial torsion load.The load and the stress at yield were recorded. The axial compression rigidity and torsional rigidity were calculated.Result1. We established a three-dimensional finite element model from L2 to the pelvis which is composed of 367363 units and 93728 nodes. The displacement at the upper edge of L5 is 1.813mm whenconstrained the roof of double acetabulum and applied a vertical load of 1000N.The maximum stress value of the upper edge of the L5 is 19.139MPa.The axial compression rigidity of the model is 551.572N/mm. The angular displacement of the model when applied 7N/m bending load in flexion, extension, right lateral flexion, left lateral flexion, right rotation, left rotation conditions were5.64115°, 5.56884°,2.10190°,2.10357°,2.18661°,1.42659°.The average axial torsional rigidity is 4.05 N-m/°. The axial compression rigidity and torsional rigidity of the model were equal to other studies. The distribution of the stress and displacement were also the same as the actual situation.2. The maximum stress of the complete model is 195.3 MPa, single iliac screw model is 189.5 MPa, dual iliac screw+titanium cage model is 149.2Mpa when constrained the roof of double acetabulum and applied a vertical load of 1000N. The axial compression rigidity of the complete model is 551.572N/mm, the single iliac screw model is 613.87 N/mm and the dual iliac screw+titanium cage model is 1683.50 N/mm. The bending rigidity of the dual iliac screw + titanium cage model is bigger than single iliac screw model which is bigger than complete model at 6 directions when applied 7N/m bending loads. The maximum stress of single iliac screw model is bigger than dual iliac screw+titanium cage model which is bigger than complete model. The maximum stress of single iliac screw model is 113.013MPa at flexion and 113.677 MPa at extension. The stress concentrated at the connecting rod below the L4 pedicle screws and upper of the iliac screws.3. Group 5 were more stable than the other groups and not yield. The yield load of group1 to group 4 were 203.1±8.0,188.9±7.5,165.7±7.2,239.2±9.8N. The yield stress of group1 to group 4 were 288.9±9.2,278.7±8.9,241.3±9.1,340.7±8.4MPa. The axial compression rigidity of each group were 152.33±8.15,123.21±7.68,112.67±9.13, 172.62±8.02,194.58±7.19 N.mm, the axial torsional rigidity were 1.43±0.12,1.02±0.12, 0.98±0.11,1.73±0.10,1.96±0.09 N. m/ °. The axial compression rigidity and torsional rigidity of Group5 > Group4> Group 1.The group2 and group3 were lower than Group 1.There was no significant difference between the group2 and group3 (P>0.05).Conclusion1. The three-dimensional finite element model of human L2-pelvis precisely and accurately can effectively reflect the biomechanics characteristics of the lumbopelvis so it can be used in the later study.2. The dual iliac screw+titanium mesh cage reconstruction can effectively restore the stability of the lumbosacral area. The stress of the internal fixation system is smaller and more dispersed.3. The single iliac screw reconstruction also can restore the stability of the lumbosacral area but the stress of the internal fixation system is bigger and more concentrated lead easy to fatigue fracture and loosening.4. The stress of single iliac screw reconstructioninternal fixation system when applied the axial compression load, flexion and extension bending load is very large. It shows that single iliac screw reconstruction is more prone to failure in the axial compression, flexion and extension loads.5. The anterior column support can effectively increase the axial compression rigidity and torsional rigidity of the model so it’s very important for the reconstruction of the stabilityof the lumbosacral region.6. The stress of the internal fixation system can be effectively dispersed after the addition of anterior column support. The risk of internal fixation failure is reduced.7. The dual iliac screw reconstruction also can effectively restore the stability of the lumbosacral area. It’s more stable than that of the single iliac screw reconstruction system.8. If the lesion of lumbosacral region is very large, we recommended the use of dual iliac screw and titanium mesh cage support reconstruction. It can effectively restore the stability of the lumbarsacral area and reduce internal fixation failure risk, improve the success rate of operation. |
PDF Full Text Request