| Background:Acetabular fracture as a special type of pelvic fracture, due to the affected to the hip joint surface, belongs to the intra-articular fractures. The injury is usually caused by directly violence, and the most common reasons for the injury are over whelmingly due to blunt trauma, crush-related injuries, falling and traffic accidents. According to a 2014 bilateral acetabulum fracture epidemiology comparison study, shows that with the continuous expansion of industry, construction and the fast rises in number of motor vehicles,2005-2012, the occurrence of the pelvic and acetabular fractures showed a trend of increasing year by year, the young male is the main injured people. As the world’s population aging increased, the patients age has a trend of rising too.The anatomic structure of acetabulum parts is complex and deep, the surgery treatment is difficult. The postoperative complications such as traumatic arthritis and heterotopic ossification occurrs often. It has become the focus and difficulties of the traumatic orthopedics research. In the past half century, the surgical skills and people’s understanding of this kind of fracture increases, for acetabular fractures,in the clinic, surgery is the first choice, especially for comminuted acetabulum fractures relate to weight bearing area. Open reduction and internal fixation has become the "(Gloden standard". However, the traditional open surgery goes with the surgical complications risks such as blood loss, peripheral nerve vascular injury and infection. In recent years, scholars tried the method of percutaneous lag screw in the treatment of no displacement and/or mild displacement type of acetabulum fractures with the help of intra-operative imaging equipment. This method not only has the benefits of limiting invasive, less blood loss and low incidence of heterotopic ossification, but can bring limb to early functional exercise, reduce the time in bed, conducive to a satisfactory functional recovery. Therefore, this technology has become a important research direction of the minimally invasive treatment of pelvic acetabular fractures.As the main part of the conform of the acetabulum, the posterior column often been involved when the fractures happened. The current studies have shown the feasibility of using percutaneous retrograde lag screw fix the acetabulum posterior column fracture. Scholars at home and abroad carried out a large number of related research, mainly including the anatomy of nailing way and the methodological research. At present, the percutaneous retrograde lag screw procedure generally choose the ischial tuberosity as the needle point, but the ischial tuberosity bone surface area is a rough arc, lack of positioning marks, the needle point selection is difficult. And surrounding tissues around the posterior acetabulum column structure is complex, osseous channel is long and narrow, with thin bone, it has the risks bolts through the bone plate or into hip joints, causing postoperative complications such as traumatic arthritis or iatrogenic neural vascular injury, now has became the main reason for the limiting of clinical application for this technic. Due to the difficulties, some scholars put forward the technic by inserting the nail via small sciatic notch, compare to traditional methods, thinking this method possesses easy to locate and has the advantage of biomechanical stability, but because of the different of peoples and experimental method, the related experimental data differences, and relevant biomechanical experiments has not been reported.With the continuous development of computer technology, using three-dimensional software we can build the 3D model of pelvis, precisely measurements the related anatomical data, and through the assignment of a material, the corresponding finite element model is established. Simulatting the physiological condition, stress been applied, we can evaluate the biomechanical stability of fracture internal fixation, it has the characteristics of high repeatability, cost savings and reliable. This study choose the two kinds of typical clinical optional nailing solution, with volunteers pelvic CT scan data for materials, application of three-dimensional modeling and finite element analysis technology, measurement the anatomical data and compare the biomechanical stability at the same time, so as to provide reference for clinical application.Objectives:1. Use the three-dimensional model of pelvic, simulatting the two different methods in insertion of posterior column lag screws, measure the related data of acetabulum column osseous channel, comparing the differences, providing the anatomical basis for the following biomechanical analysis.2. On the basis of the understanding of pelvic anatomy, using finite element software, establish a three-dimensional finite element model of the pelvis, and analyzes the reliability and validation of the model, and discuss the effect as a clinical research methods.3. On the basis of finite element model of pelvis, we set up two different kinds of posterior column acetabulum fracture models using retrograde lag screw as internal fixation, simulated physiological state, evaluate the biomechanical characteristics of two kinds of internal fixation way.Methods:1. Collection of images and anatomical measurement:Obtained 32 adult patient randomly, who took complete CT scan of pelvis in our hospital between September 2012 and September 2014 without any bony andanatomy abnormality and desease.17 males,15 females are obtained. The images were output in the form of DICOM and then inputted into Mimics 14.1 to reconstruct the pelvis by digital three-dimensional reconstruction techniques. The anatomical sites were marked and the relevant anatomical parameters of posterior column of acetabulum were measured.2. The construction of fracture model and the assembly of finite element model: An healthy adult male volunteer was selected and the X-ray test was applied to exclude lesions and mutation of pelvic. Then the spiral CT scan, with the slice thickness of 0.5mm was conducted to get pelvic tomography image data. The data was imported into Mimics 14.1 software to build a three-dimensional model of the pelvic bones, then the model was imported into Freefromã€Geomegic Studio software for smooth handling and simulated posterior column osteotomy. Adding the pelvis adjacent structures, such as ligament. The finite element models of pelvis is established, applying the vertical stress, verify its validity.3. The establishment of model of retrograde lag screw internal fixation of posterior column acetabulum fracture and finite element analysis:Refer to the relevant literature, simulated the posterior column osteotomy, set up two different kinds of fracture fixed models, simulation the standing and sitting position, applying a 500N vertical stress, analysis the biomechanical stability of two different kinds of the fixed models in different physical location, evaluation index for stress and the displacement.4. Statistical analysis:The data obtained were analyzed by the software of SPSS19.0. The independent sample t-test and paired samples t test were used. Compare the differences between different gender and different internal fixation solution, the numerical results using mean±standard deviation (x±s) said.Results:1. Based on the original pelvic CT scan data, we established the 3D model of pelvic. Using software Mimics, we can measure the space angle and distance. Measurement results are as follows:The ischial tuberosity group:the angle to the coronal plane is (11.69±4.79)°or male and (8.36±3.24)°or female, the angle to the sagittal plane is (10.34±3.60)°or male and (12.56±3.48)°or female. The differences between the angle to sagittal and coronal plane were of statistical significance (P<0.05) between the male and female. The lesser sciatic notch group:the angle to the coronal plane is (39.73±5.69)°or male and (40.49±5.06)°or female, the angle to the sagittal plane is (18.46±5.72)°or male and (16.11±6.62)°or female, and there is no significant differences between male and female (P>0.05). The mean maximum diameter of virtual cylindrical implant was (9.32±1.84)mm for male and (8.51±1.59)mm for female. The mean length of virtual cylindrical implant was (141.16±10.23)mm for male and (125.72±6.43)mm for female in the ischial tuberosity group and (115.03±11.19)mm for male and (91.38±9.96)mm for female in the lesser sciatic notch group. The differences of the length and diameter between the group male and female were of statistical significance (P= 0.001< 0.05).2. The establishment of pelvis three-dimensional finite element model. The model was divided into 490227 nodes and 295806 units. The maximum stress value was 32.45 Mpa, located around the greater sciatic notch, the maximal displacement value of 0.34 mm, is located in the sacroiliac joints, the stress distribution is symmetrical, the pelvic model we established can meet the demand of biomechanical analysis.3. The lag screw fixation in posterior column fracture of acetabulum model is divided into four groups:ischial tuberosity standing position group, ischial tuberosity sitting position group, lesser sciatic notch standing position group, lesser sciatic notch sitting position group. Applied the stress, stress distribution and displacement of the fracture line and internal fixation was record respectively. For the standing position proup the maximum stress of internal fixation was 6.52Mpa and 6.75Mpa, and 14.01Mpa and 36.05Mpa in sitting group. The stress of lesser sciatic notch group is higher than ischial tuberosity group. Fracture line displacement for lesser sciatic notch standing position group was (4.23±1.27)μm, lesser sciatic notch sitting position group was (6.45±0.44)μm, ischial tuberosity standing position group was (4.05±1.31)μm and ischial tuberosity sitting position group was (7.27±0.48)μm. The differences between the sitting groups were of statistical significance (P= 0.003< 0.05).Conclusions:1. With the use of software of Mimics and original CT scan data, the three-dimensional model of pelvic was established and has a high degree of geometric similarity, and the relevant measurement data is accurate and reliable. The finite element model of pelvis established based on this three dimensional model reflects the pelvic biomechanical properties, can provide reference for clinical application.2. After the comparison of two different posterior column retrograde lag screw fixation method, it is concluded that using the lesser sciatic notch nailing method has a low level of stress and displacement of fracture than using the ischial tuberosity nailing method, suggestting the lesser sciatic notch nailing method has certain biomechanical advantages, but the application need combined with the specific condition of patients.3. There has some deficiencies in this study, the sample size is small and using the finite element analysis method, the bone was set to be homogeneous and the same properties of materials, pelvic osseous structure is complex, cancellous bone and cortical bone has a different density distribution, so there is a difference between the biomechanical results and the actual situation, and due to the complexity of fracture line direction, the fracture model cannot meet the demand of all the biomechanical analysis of acetabulum posterior column fracture internal fixation. |
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