| ObjectivesPelvic fracture is one of Severe and complicated damage, which caused by traffic accident, crash, fall and project accident. Among of them, traffic accident is in ratio of 25%～84.5%. the mortality rate is 5%Y20%, and the disability rate is 50%～60%.The clinical characteristic of pelvic fracture is high-energy and complex lesion, including the lesion of bone, hemorrhagic shock, chest, abdomen, urethra and nerve. The effect traditional expectant treatment and external fixation therapy is very poor. The long- time complication of severe pelvic fracture is 57%, according to the Semba's investigation. Now with the improvement of recognition about pelvic physiological pathological anatomy, severe pelvic fractures are managed with ORIF (open reduction with internal fixation).In order to improve therapeutic effect of pelvic fracture, the knowledge on relationship between the type of pelvic fracture and the anatomic structures, such as pelvis, important ligaments, adjoining vascular nerves was reviewed. Firstly, in our study, we attempt to reconstruct a precise pelvic three-dimensional (3D) medical image based on the 2D slices. Secondly, a 3D finite-element modeling will be reconstructed based the former by, turning to professional computer software. Of course, this modeling must be validated before being utilized. Thirdly, the two ORIF operation methods about C-typical pelvic fracture on 3D finite-element modeling will be simulated, according to the clinical the dislocation of sacroiliac joint. The biomechanical stability and intensity of internal fixations will be analyzed and compared. Finally, a simple, efficient, and low-cost method will be found, which must benefit for the clinical and fundamental research on pelvic. According, this method will make for the improvement of therapeutic efficacy of pelvic fracture.Materials and Methods1. Knowledge on relationship between the type of pelvic fracture and the anatomic structures, such as pelvis, important ligaments (sacrosciatic ligament, sacrotuberal ligament, sacrotuberal ligament, posterior sacroiliac ligament, interosseous sacroiliac ligament, sacroiliac articular cartilage, pubic symphysis) ,adjoining vascular nerves was reviewed, including clinical anatomy relevant to the two ORIF.2. One common volunteer was chosen who was scanned by multi-slices computerized tomography (MSCT) in Medical Image Centre of Nan fang Hospital. Scan plane was situated between the bottom of Fourth lumbar vertebra and the plane of pelvic outlet (namely, inferior margin of ischial tuberosity). Scanning thickness of each slice was 0.625 millimeter. All the slices were saved in the format of the DICOM (Digital Imaging and Communications in Medicine). Therefore, the 2D image data in format of DICOM was obtained, and there were 410 2D-CT slices. Then these 2D-CT slices were imported into the three-dimensional reconstruction software of Mimics (Materialise's Interactive Medical Image Control System). From this data, a three-dimensional image about pelvis was reconstructed with the software, Mimics which is the professional computer software applied to the medicine field and produced in Belgium. Then this 3D image was modified, smoothened and surface-meshed with the software of Freeform. Finally, the 3D solid modeling of pelvis was reconstructed successfully. Final outcome was saved in the format of IGES (Initial Graphics Exchange Specification).3. The 3D solid modeling of pelvis was imported into the ANSYS, a largely-scale universal finite-element analysis software. Pelvic accessory structures, such as ligament, pubic symphysis, were added to the 3D modeling with powerful pre-processing modular of ANSYS. Finally, the integrated 3D finite-elemental modeling of pelvis was reconstructed, and the efficacy of this modeling was also validated. When the efficacy was validated, it could be applied into next procedure.4. In order to simulate ORIF with plates and screws on dislocation of pelvic sacroiliac joint via anterior path, the two reconstructing plates and the six standard screws were added into the model, as well as the two sacroiliac joint lag screws via posterior path. The 3D finite-elemental modeling of the dislocation of pelvic sacroiliac joint was reconstructed according to the clinic. The two ORIF operation methods about C-typical pelvic fracture on 3D finite-element modeling will be simulated, according to the clinical the dislocation of sacroiliac joint. Then the attribute of materials were defined. After that, the modeling (including all the structures) was meshed by the tool of self-adaptation meshing function by being controlled meshing density. Then the vertical load pressure(500 Newton) was exerted on the upper terminal plate of first Body of sacrum, and the border of two-sides acetabulum were constrained. After that, the none-line solution was analyzed. When the procedure of the solution was done, the stress and strain nephograms were obtained with the function of post-processing module. Finally, the biomechanical stability and intensity of internal fixations will be analyzed and compared.Results1. The stability of pelvic ring mainly depends on the integrity of ligament structures, mainly posterior ligament structures. There are many kinds of injury patterns, and every pattern has special ligament lesion. The clinical anatomy of the first sacral vertebrae (S1) and peripheral important structures is very significant to the therapy of sacroiliac dislocation clinic.2. A serial precise of data of DICOM format were Obtained with MSCT scanning. Finally the solid modeling was achieved by being reconstructed by the software of Mimics, and being modified by the software of Freeform, which possess many functions, such as modification, surfacing, getting rid of noise, et al.3. The 3D solid modeling of pelvis was imported into the ANSYS. The precise 3D finite-elemental modeling of pelvis was obtained with the function of pre-processing modular in ANSYS, such as meshing tool. The modeling possesses 266,826 nodes and 170,456 elements. Among of them, the cortex bone, cancellous bone, pubic symphysis articular cartilage and the internal fixation materials are all the solid32-elements, and the ligaments are all the link-elements.4. The none-line analysis was carried out by exerting stress, and the results indicated that the modeling is stable, the ligaments were reasonable added to the modeling, and the stress was relatively concentrated in greater sciatic notch. This result is close to the fact.5. The two ORIF methods were simulated and analyzed. From the stress and strain nephograms, we can conclude that the max stress is 0.525E+09Pa; the stress was relatively concentrated in the combining site between screws and plates when the dislocation of sacroiliac joint was treated with two plates via anterior path, and the displacement of sacrum is downward, forward and rightward. The total displacement is 0.294E-03m. But when the dislocation of sacroiliac joint was treated with two screws via posterior path, the max stress is 0.321E+08Pa, the stress was relatively concentrated in the combining site between the left iliac and lag screws, and the total displacement is 0.838E-04m. From the nephograms of ORIF materials, we can conclude that the stress is mainly concentrated between screws and plates, and at the medial end of the plates when dislocation of the sacroiliac joint was treated with two plates. Meanwhile, the stress is mainly concentrated on the four medial screws. But the total stress on the screws is less than that of the site between the plate and screw. Therefore, the breakdown of screws firstly happened on the site between the screws and plates when the enough yield stress was exerted. As the two screws were concerned, the stress was mainly concentrated on the site between screws and iliac, and more than those of the site of screw cap and point. So the breakdown of screws firstly happened on the site between the screws and sacrum when the enough yield stress was exerted.The biomechanical stability and intensity of the two methods of internal fixations were analyzed and compared. The consequences indicate that the fixation stability of two sacroiliac joint lag screws is larger than that of two reconstruction plates via anterior path. The total displacement of the former is less then that of the latter, and the stress of the former was not clearly concentrated on some sites. Therefore the results are of coincidence to that of the scholar overseas.Conclusions1. The stability of pelvic ring mainly depends on the integrity of ligament structures, mainly posterior ligament structures. There are many kinds of injury patterns, and every pattern has special ligament lesion.2. The method of this study is that: One common volunteer was chosen, who was scanned by multi-slices computerized tomography (MSCT), then the 2D image data in format of DICOM was obtained, and then, from this data, a three-dimensional image about pelvis was reconstructed with the software of Mimics. Finally this 3D image was modified and smoothened by the software of Freeform and the 3D solid modeling of pelvis was reconstructed successfully. This method is very quick, convenient, high efficient, precise.3. The 3D finite-elemental modeling was reconstructed according to the clinic. The two ORIF operation methods about C-typical pelvic fracture (dislocation of pelvic sacroiliac joint) on 3D finite-element modeling were simulated, according to the clinical the dislocation of sacroiliac joint. The biomechanical stability and intensity of internal fixations were analyzed and compared. In the end, the consequence of this study is that the fixation stability of two sacroiliac joint lag screws is larger than that of two reconstruction plates via anterior path. This conclusion is of coincidence to experimental results done by others by means of biomechanics experiment with cadavers of the man.4. The finite-elemental method is applied to biomechanics experiment in pelvic successfully. This method possess many advantages, such as purity, low-cost, low time consuming, high efficiency, precise simulation, favorable repeatability. Also this method can complement with objective experiments each other.5. Based on this 3D finite-elemental modeling of pelvis, many relative studies can be expanded in the future. For example, other pelvic lesion patterns can be easily simulated on this modeling. We desire for improving therapeutic efficacy of pelvic fractures clinically in the future.6. The disadvantage of this test is that all the biomaterials were supposed to homogeny, continuous and isotropy. But that is not different from the fact.7. The finite-element method and the method of biomaterial test of the specimen have respectively advantages and disadvantages. The two methods should make up each other, then the more scientific and reasonable results can be obtained finally. |
