| BackgroundUnstable pelvic fractures resulted mostly from high-energy injury, particularly open pelvic fractures, often associated with serious blood vessels and nerves injury, and have higher mortality and morbidity. The aim of treatment is to reconstruct the stability of the pelvic ring. Previous studies have shown that 60% of pelvic stability comes from the posterior pelvic structures, and 40% from the anterior structures. So, it is important to reconstruct the stability of posterior pelvic ring structures in the treatment of pelvic injury. Now many ways can be used for the treatment of posterior pelvic structures, these ways have advantages and disadvantages respectively, and the indications are different.The treatment of posterior pelvic ring injury with tension band plate has the advantages of convenient, less tissues damage, less complications. Tension band plate has been used generally in the treatment of posterior pelvic ring injury. In the previous studies, the position and the orientation of tension band plate are different. The biomechanical analysis of three internal fixation ways which are used generally in clinical medicine has been done by Guo-qing Tan. But the further study is needed to verify the position and orientation of the tension band plate.The finite element analysis is an important way for the biomechanical study in the theory. The finite element analysis is used to build the pelvic 3D model, simulating the real human pelvic structures, to analyze the strain, stress and displacement distribution of pelvic model under a given load.In this study, the position and orientation of pelvic ring central plane were verified by the anatomy of human pelvic specimens. On this basis, the finite element analysis pelvic models were built; the effect of different tension band plate for the pelvic injury was analyzed by the finite element analysis.PART 1 Anatomy studies for unstable posterior pelvic ring disruptions treated with tension band plateObjectiveThe aim of this study is to verify the position and orientation of pelvic ring central plane by the anatomy of human pelvic specimens and AutoCAD, Mimics software. The distance from posterior superior iliac spine (PSIS) to pelvic ring central plane was measured.Methods12 adult cadaver pelvic specimens, male 8, female 4, were used in this study. The sacroiliac joints and pubic symphysis were separated to exposure the joint faces of sacroiliac joints and pubic symphysis. CT data of 20 normal pelvises were acquired to be used in the next study. Three different ways were used to study the normal pelvic structures:first, the pelvic specimens study was used, the sacroiliac joint and pubic symphysis were fitted to regular geometric shape, the center of gravity of sacroiliac joint and pubic symphysis were verified, then the pelvic ring central plane was verified. The distance from ilium posterior superior spine to pelvic ring central plane was measured. And the orientation of pelvic ring central plane was measured. Second, AutoCAD was used to study the pelvic structures. The pictures of medial sides of ilium were acquired by camera. The position and orientation of pelvic ring central plane were verified by the AutoCAD software, the way was same to the first way. Third, Mimics software was used to study the pelvic structures. The pelvic models were built using the CT data. The position and orientation of pelvic ring central plane were verified on the pelvic models. Statistical analysis was performed using SPSS software.ResultsThe pelvic specimens study:the distance from ilium posterior superior spine to pelvic ring central plane was 26.13±1.53mm, the orientation of pelvic ring central plane was 54.00±0.78°, referencing from the line between ilium posterior superior spine and ilium anterior superior spine. The AutoCAD study:the distance from ilium posterior superior spine to pelvic ring central plane was 26.45±1.49mm, the orientation of pelvic ring central plane was 54.75±0.94°. The Mimics study:the distance from ilium posterior superior spine to pelvic ring central plane was 25.62±0.95mm, the orientation of pelvic ring central plane was 55.46±0.51°. The total results:the distance from ilium posterior superior spine to pelvic ring central plane was 25.87±0.80mm, the orientation of pelvic ring central plane was 55.05±0.45°.ConclusionsThe position and orientation of pelvic ring central plane were verified, the pelvic ring central plane was located ante-superior to the ilium posterior superior spine. The distance from ilium posterior superior spine to pelvic ring central plane was 25.87±0.80mm, and the orientation of pelvic ring central plane was 55.05±0.45° eferencing from the line between ilium posterior superior spine and ilium anterior superior spine.PART 2 Construction and examination of three-dimensional finite element model of pelvisObjectiveTo build the 3D normal pelvic finite element model, and examine the reliability of the model, to lay the foundation for the further study.MethodsA healthy adult male was recruited. The cross section pictures of pelvis were acquired by computerized tomography (1.0mm slice thickness). The pictures were imported into Mimics software to build the 3D pelvic models. The model was optimized by Geomagic Studio software, and then was imported into ABAQUS software to build the pelvic finite element analysis model. To simulate the standing human, the bilateral acetabulum was constrained, and a vertical 600N was loaded on the superior surface of endplate of sacrum.ResultsUnder 600N vertical load on sacral endplate, the stress passed from sacral endplate to bilateral acetabulum, passing through bilateral sacral wing, sacroiliac joint, arcuate line and greater sciatic notch. The tendency of sacral displacement was ante-inferior, and the tendency of ilium was rotation. The strain was concentrated at sacroiliac joints, and the strain of total model was small.ConclusionsThe 3D finite element model of pelvis was built successfully. The model was reliable, can be used for the finite element analysis. The finite element analysis provides a new method for the biomechanical studies of orthopedics.PART 3 Finite element analysis for unstable posterior pelvic ring disruptions treated with tension band plateObjectiveUsing the finite element analysis, compare the effect of different optional tension band plate which was used to treated sacroiliac joint dislocation, to find the optimal option of tension band plate.MethodsThe way of building the injured pelvic finite element model was similarly with the part 2. The models of plates and screws were built with Solid Works software, and then they were imported into ABAQUS software and assembled with the injured pelvic model to build the internal fixation models. According to the position and orientation, six fixation models were built:iliac posterior anterior superior(IPAS) model、iliac posterior anterior inferior(IPAI) model、iliac posterior anterior horizontal(IPAH) model、iliac superior anterior horizontal(ISAH) model、iliac superior anterior inferior(ISAI) model and iliac inferior anterior superior(ⅡAS) model. To simulate the standing human, the bilateral acetabulum was constrained, and a vertical 600N was loaded on the superior surface of endplate of sacrum. The displacements of left sacroiliac joint were recorded. Statistical analysis was performed using the analysis of t-test,comparing between any two models.ResultsUnder 600N vertical load on sacral endplate, compared with normal pelvic model(0.070144±0.00284mm、0.550724±0.007925mm), the displacements of sacral side and iliac side of left sacroiliac joint were 0.524677±0.009845mm 0.947979±0.096923mm, the difference was statistically significant (P<0.001). The displacements of sacral side and iliac side of left sacroiliac joint in ISAI model were 0.261031±0.006321mm,0.380023±0.036695mm; ISAH model 0.292494± 0.009099mm and 0.558186± 0.038701mm; IPAS model 0.313834±0.009324mm and 0.483707±0.044013mm; IPAI model 0.257551±0.008835mm and 0.354244± 0.040038mm; IPAH model 0.272655±0.009401mm and 0.362496±0.043095mm; HAS model 0.295074±0.010359mm and 0.626016±0.045346mm. The displacements of fixation model were all smaller than injured pelvic model, the difference was statistically significant (P<0.05). Among the IPAI model, IPAH model and ISAI model, the displacement of IPAI model is smallest, but the differences were not statistically significant among the three. The displacement of ISAI model was smaller than ISAH model, IPAI model and IPAH model smaller than IPAS model, IPAS model smaller than HAS model.ConclusionsThe "hoop" structure of total pelvic ring should be considered in the treatment of pelvic ring injury. After the finite element analysis, the effect of IPAI model, IPAH model and ISAI model were better than the other three models. The effect of models in which the orientation of plate was parallel to pelvic ring central plane was better; the effect of models in which the position of plate at posterior superior iliac spine was better, but the differences were not statistically significant compared with the position 26.0mm superior to PSIS; the position inferior to PSIS was worst. Association with the part 1, the best position of tension band plate was located between the PSIS and the position 26.0mm superior to PSIS, and the best orientation was parallel to pelvic ring central plane which was about 55.0°ante-inferior referencing from the plane of ilium posterior superior spine and ilium anterior superior spine. |
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