| Research backgroudWith the development of modern society, pelvic and acetabulum fracture increase year by year combined with the incidence increase like the high falling down injury and traffic accident injury. Studies have shown that pelvic fractures accounted for 1%-3% of whole body fracture, although it’s incidence rate is less than extremities fractures and spinal fractures, but it’s incidence of the uncontrolled hemorrhagic shock(estimated at 40%) is more than the extremities fractures and spinal fractures, and the mortality of pelvic fractures is 10.2%. Pelvic fractures caused by low energy are more stability and easily to handle with.These kind of patients generally can recover smoothly.Pelvic fractures caused by high-energy injuries are more complicatedly and seriously, the incidence of malunion and traumatic arthritis is as high as 50%-60%, mortality rate of these kind of patients is as high as 20%. In view of the high rate of mortality in the pelvic fracture, it is necessary to do further research for the pelvic fractures.The literature record of the pelvic fractures began in the 19th century, Malgaine described half pelvic fracture dislocation for the first time. Since then, Pennal systematically classified the pelvic fractures for the first time. The classification of pelvic fractures including tiles, Young and Letoumel classification. With the deepening understanding of pelvic fractures, the operation has become an effective means for the treatment of unstable pelvic fractures. Since the 1980s, foreign orthopedic surgeons began to treat pelvic fractures by open reduction and internal fixation widely. But because of the anatomy of the pelvic is complex and the fractures of pelvic is comminuted, it is difficult to obtain a clear operation field and the neurovascular injury is inevitable. Now more and more orthopedic surgeon works hard to treat pelvic fractures by minimal trauma and want to obtain stable curative effect. In recent years, along with the development of operation skills and imaging technology, the minimally invasive percutaneous treatment of pelvic fracture increasingly because of little injury, less bleeding and less incidence of complication.The pelvic ring has a special anatomical structure, the anterior part is the symphysis pubis and pubic rami, which accounted for 40% of the pelvic stability, and the posterior structures of the pelvic accounting for the last 60%. Anterior pelvic ring instability is due to pubic symphysis separation or pubic rami fractures, and the posterior pelvic ring instability is due to to the sacroiliac joint injury or capsular ligament damage. The treatment of anterior pelvic ring injuries experienced tension band wire, steel plate, external fixation and other treatment methods. In recent years, with the development of minimally invasive operation equipment and improvement of monitoring system in the operation, minimally invasive operation in treatment of pelvic fracture become more and more popular. Dortor Guo’clinical practice showed that closed reduction and percutaneous fixation of unstable pelvic ring has a little injury, less bleeding and many other advantages, but he has also found that due to the high variability in special anatomical, this kind of surgery has certain complications. There are reports of wrong percutaneous screw placement may damage the iliac vessels, spermatic cord, sacral nerve and other important structures and which may cause serious complications. This study is conducted to the anatomic measure of anterior pelvic ring region and provide the reference for the development of minimally invasive operation.Over the years, the traditional research methods for the bone biomechanics including clinical observation and cadaver specimens simulation. These two research methods are affected by many factors, such as specimen source and individual differences. Since 1972, Brekelmans applied the method of finite element analysis to the bone biomechanics research for the first time, a lot of scholars apply this kind of method through three-dimensional reconstruction and virtual operation to improve the success rate of operation. The digital medicine provides a novel therapeutic strategy for the orthopedics surgery simulation.In this study, by collecting the pelvic’ CT scan data and combining with the computer aided system, we established the finite element model of anterior pelvic ring injury. By using the virtual operation function on MIMICS, Models of cannulated screw internal fixation and reconstruction plate screw internal fixation were both established. Then, Non-linear FEA was performed after loading, we observe the stress distribution characteristics of bone and tissue through stress and strain nephograms. And at last we using 3D print mode to simulate the plate and screw implantation through treating superior pubic rami fractures.In order to verify our hypothesis, we do the following three parts of researchs, And the results will report as follows:PART 1 Anatomical Measurement and Finite Element Study on Screw Channel Parameter in Percutaneous Fixation of canulated Screw for SymphyseolysisPurposeTo provide anatomical basement for treatment of symphyseolysis with percutaneous fixation of canulated screw, through anatomical measurement on pubic symphysis and the surrounding tissues, combined with research on screw channel parameters of percutaneous fixation of canulated screw in the treatment of symphyseolysis.Methods20 cases of normal pelvic specimens from embalmed adult cadavers were taken to measure the anatomical parameter of bony remark of pubic symphysis and the space between spermatic cord (round ligament of the uterus) and pubic tubercle.3D finite element model of pelvis was established to simulate the fixation for symphyseolysis. The distance from entry point to outer edge of pubic tubercle and the angle of canulated screw with horizontal plane were measured with the software.ResultsAnatomical measurement results showed that the narrowest diameter of the superior ramus of pubis is 9.137±1.189mm, distance between two pubic tubercles is 55.656±3.780mm, thickness of the upper pubic symphysis is 10.510±0.814mm and distance between upper and lower pubic symphysis is 40.872±1.211mm, the distance between round ligament of the uterus and pubic tubercle is 4.408±0.304mm, and the distance between spermatic cord and pubic tubercle is 5.196±0.351mm. The distance from corona mortis vessels to the pubic tubercle is 44.5mm.The angle between canulated screw guide pin and horizontal plane is 8.342±2.152°, between guide pin and coronal plane is 5.236±1.612°, and the distance from entry point to the outer edge of pubic tubercle is 10.013±1.145mm measured by Mimics software. At last percutaneous surgery was simulated on the cadaver through the above data, and we find the screw was placed correctly in postoperative imaging examination.ConclusionsAccording to the anatomical data and finite element studies of screw channel parameter in percutaneous fixation of canulated screw for symphyseolysis, the method can improve the accuracy of screw placement and reduce complications. 55.656±3.780mm, thickness of the upper pubic symphysis is 10.510±0.814mm and distance between upper and lower pubic symphysis is 40.872±1.211mm, the distance between round ligament of the uterus and pubic tubercle is 4.408±0.304mm, and the distance between spermatic cord and pubic tubercle is 5.196±0.351mm. The distance from corona mortis vessels to the pubic tubercle is 44.5mm.The angle between canulated screw guide pin and horizontal plane is 8.342±2.152°, between guide pin and coronal plane is 5.236±1.612°, and the distance from entry point to the outer edge of pubic tubercle is 10.013±1.145mm measured by Mimics software. At last percutaneous surgery was simulated on the cadaver through the above data, and we find the screw was placed correctly in postoperative imaging examination.PART 2 Three-dimensional Finite Element Analysis on Cannulated Screw Fixation and Reconstruction Plate Screw Fixation in Treatment of Pubic Symphysis DiastasisPurposeThis study was designed to compare dynamic stability and biocompatibility between cannulated screw fixation and reconstruction plate screw fixation in the treatment of pubic symphysis diastasis (PSD) and to provide clinical guidance for the choice of internal fixation.MethodsThe CT scans were performed in the patient with pubic symphysis diastasis and 3D finite element analysis (FEA) model of PSD was established. The separation of the symphysis pubis was reduced via the virtual operation function on MIMICS. Models of both cannulated screw internal fixation and reconstruction plate screw internal fixation were established. Non-linear FEA was performed after loading. The stress distribution characteristics of bone and implants were observed with stress and strain nephograms.ResultsComparative analysis of stress and strain nephograms showed that the stress distribution of cannulated screw fixation was more even and the stress concentration was much less than screw-plate group. Stress potentially concentrated on screw-plate contact site in the screw-plate group, thus easily causing screw loosening and even breakage. However, the average motion and the stabilities in two groups were similar after fixation. Finite element method, which has high repeatability and authenticity, is used to analyze the dynamics stability and biocompatibility of two internal fixation models for PSD.ConclusionsReconstruction plate screw fixation and cannulated screw fixation are both appropriate for the treatment of PSD, whereas percutaneous cannulated screw fixation appears to be superior to screw-plate group in treating PSD for its less possibility of screw loosening and breakage. internal fixation were established. Non-linear FEA was performed after loading. The stress distribution characteristics of bone and implants were observed with stress and strain nephograms.PART 3 Three Dimensional Finite Element Analysis of Canulated Screw Fixation and Reconstruction Plate Screw Fixation Treating Superior Pubic Rami FracturesPurposeTo compare dynamics stability and biological compatibility of canulated screw fixation and reconstruction plate screw fixation by treating superior pubic rami fractures, for providing reference for the selection of internal fixation in clinical practice.MethodsThe pelvic of superior pubic rami fractures was given CT scan. Three dimensional finite element models of superior pubic rami fractures was established, and virtual operation function was applied in MIMICS software to fix the superior pubic rami fractures. The model of canulated screw fixation and reconstruction plate screw fixation is respectively established. And the nonlinear finite element analysis was made after being loaded. The characteristics of stress distribution for bone tissue and implants were observed by the images of stress and strain.ResultsThrough the comparison and analysis on the images of stress and strain, we find that applying reconstruction plate screw fixation has balanced stress distribution and has small overall displacement compared with cannulated screw fixation. And as for cannulated screw fixation, there is a certain degree of stress concentration and the stress is in the affordable range. Applying finite element method to analyze dynamics stability and biological compatibility of two internal fixations for superior pubic rami fractures has higher reproducibility and validity.ConclusionsCanulated screw fixation and reconstruction plate screw fixation have good dynamics stability, and percutaneous canulated screw fixation is more suitable for minimally invasive therapy on clinical pelvic injury. |
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