| ObjectiveThe damage or separation of sacroiliac joint caused by trauma, tumor surgery and other causes, result in lumbosacral instability and that the patient can not be an early exercise.So it is necessary for the sacroiliac joint reconstruction. Modified Galveston technique (MGT) is one of the lumbosacral reconstruction.When the sacroiliac joints separation after the high-energy injury is greater than 0.5cm,the pelvic ring will need to be fixed. There are commonly used sacroiliac lag screw fixation and anterior plating.In 1997 Gokaslan has made use of Galveston technique after resection of sacrum for reconstruction of the sacroiliac joint.This method has become one of the reconstruction. In recent years, this method has gradually evolved into a modified Galveston technique(MGT) that are also used to fixed the sacroiliac joint dislocation. Because of lack of bio-mechanical and long-term follow-up, we do not know differences between MGT and the commonly ways in fixation. So the authors intended to compare and analysis different fixations to provide a theoretical basis and clinical applications.At the same time the framework navigation(FN) for percutaneous sacroiliac screw were studied. Currently there are two ways for percutaneous sacroiliac screw: First, repeated intraoperative X-ray determine the direction,angle and depth of screw; the second is by computer navigation,including preoperative and intraoperative positioning. Both ways have the advantages of small range of exposure, less bleeding, sufficient biomechanical stability, fewer complications, early activities, and shorter hospital stay. But the former demands that the surgeon’s are not only familiar with the anatomy of the pelvis, also the information of X-ray.Morever, a large enough field of vision and clarity are also needed. If you have a slight mistake,you will possiblely injury peripheral vascular and nerve. Although the latter can avoid this risks, but the equipment that only a fewer hospitals have is expensive. But complexity of preoperative markers limit their widespread application. At present, the technology has the following problems:firstly,how to determine the entry points;secondly,how to measure the diameter of the inserted screw; thirdly,how to determine the direction of the screw; fourthly,how to avoid the complications.At present the computer navigation has been widely used in surgical areas, but has limited the clinical applications because of the cumbersome procedures and expensive price. Present our hospital has not the three-dimensional navigation, and FN has yet not to be reported. Previous reports are based on measuring, but the measured data will be little used in clinical.This FN for percutaneous sacroiliac screws can solve the above problem, and can reach into many times, reproducibility and standardization of surgical procedures. The key of the direction of the sleeve is an accurate three-dimensional changes.1. To provide a theoretical basis for clinical application by comparing different biomechanical stability of different internal fixation (MGT and LS) for the sacroiliac joint dislocation with the three-dimensional finite element analysis (FEA).2. To designed the FN by MedCAD and cooperating with the mould companies. To provide empirical method and evidence for the personal preoperative prepare of percutanous lag screw fixation of sacroiliac joint preparation.Materials and Methods1. Collection of imagesObtained 1 adult patien in Nov,2010, who took complete CT scan of pelvis in our hospital without any bony and anatomy abnormality. Scan condition:slice increment 0.45 mm, matrix 512×512. All the images were saved as DICOM format and imported to the personal computer.2. Reconstruct the 3-dimensional model of fixation and pelvisAll the sequent tomoscan images of pelvis were imported into the Materialise’s Interactive Medical Image Control System (Mimics10.01) in personal computer as DICOM format. The 3-dimensonal models were reconstructed by "Thresholding"、"edit mask"、and" Region Growing". The model of IGES format resuled from Mimics are imported to Geomagic10.0 for geometry reconstruction. According to the criteria used in the clinic fixation, kinds of fixations are reconstructed by Solidworks2007.Finally, IGES format are exported.3. Meshing and assembling in Hypermesh10.0The original model and internal fixation are imported into Hypermesh10.0 with IGES format. The model was meshed, assembled and given the material properties in Hypermesh10.0 software. Three-dimensional finite element (3D FE) models of different fixations for sacroiliac joint dislocation were established. Finally the model was imported to Ansys10.0. The above of L4 vertebral body was compressed by the 500N axial load.To comparing the stress-strain nephogram for the different fixations, the biological mechanical stability of different internal fixations were analyzed.4. The study of the framework navigation(FN) for percutaneous sacroiliac screwIn this study, the normal CT scan data are imported into the Mimics software to establish the pelvis model. Using 3D model for simulating the insertion of lag screw, the drawing of FN are designed by MedCAD and cooperating with the mould companies. Then the FN are applied to the corpse in the operating room for skillful operations, lessons learned and appropriate improvements. After improvement of the FN, the navigation devices are used in clinical surgery. The operation time, X-ray number, the accuracy of screws, a one-time success rate and other indicators are compared between the FN and previous hand surgery. And the function of the lower limbs is assessed. Long-term follow-up of patients after discharge, and to assess the results. The design and application of the FN can solve the surgical problems in fixations of sacroiliac joint dislocation with percutaneous screw.ResultsAfter FEA stress analysis on the vertical load at the top of L4 vertebral body in different models of sacroiliac join fixation, post processing module generated the various parts of strain and stress contours. All of the experiments showed no fracture fixation. Apart from different fixations, other conditions are identical, so the FEA of five internal fixations have good comparison. From the sress and strain nephograms, the pelvic max stress of 5 different fixatons,which are d L4-Ⅰgalveston, d L5-Ⅰgalveston, s L4-Ⅰgalveston, s L5-Ⅰgalveston, is 1.690×109 Pa,1.131×109 Pa, 0.834×109 Pa,0.836×109 Pa,1.584×109 Pa. The displacement of sacrum is downward, forward, and rightward. The total displacement is respectively 1.589×10-3m,1.871×10-3m,2.404×10-3m,2.468×10-3m,0.3083×10-3m. The max displacement of bilateral fixed is smaller than that of the unilateral fixed with MGT. Whether bilateral or unilateral,the max displacement was no significant difference between L4 and L5, but they are larger than that of LS fixation. LS can be fixed with the posterior ring as a whole, and will lead to the deformation of the double sacroiliac joint with the axial load. The reason is possibly that MGT is similar to the " bridge plate" principle.Under a variety of internal fixation Von Mises stress located in the binding site between lumbar and iliac screws and bone, which demanded higher the elastic modulus of screws and bone density.2. The study of the FN has an initial results, but it too simple, no application of specimens. Cooperated with the mould company, CAD drawings had improved for many times. After improvement of the FN, the navigation devices are used in clinical surgery. Our team will continue to study this device, improve and perfect it. Application of the FN needs to sum up in practice,.Conclusions1. For unilateral dislocation of the sacroiliac joint, the max displacement of bilateral fixed is smaller than that of the unilateral fixed with MGT. Whether bilateral or unilateral,the max displacement was no significant difference between L4 and L5, but they are larger than that of LS fixation. Because this technology is longer and more expensive than the lag screw fixation. Therefore, when the dislocation of the sacroiliac joint (or a combination of sacral fracture DenisⅠ,Ⅱ) is no significant, the author proposes to give the lag screw fixation. But on the obvious displacement or failure of closed reduction, modified Galveston technique is an alternative way.Ignored the difference between cortical and cancellous bone,but this simplify are little influence in the motion of the sacroiliac joints and stress distribution. In this study, biomechanical testing have not been compared. But the FEA and biomechanical test have its advantages and disadvantages. In order to obtain more scientific and reasonable results, in the future, they should be combined, comprehensive evaluation.2.The combination of reverse engineering and pelvic three-dimensional model provides not only a new application of research methods, but also a simple, intuitive operation for the sacroiliac joint dislocation with percutaneous screw fixation preparation. Preliminary studies have made some progress. our team will continue to give verification. |
PDF Full Text Request