The Finite Element Analysis Of Both-column Fractures With The Contralateral Anterior Pelvic Ring Unstable Of Acetabulum Fixed By Dynamic Anterior Plate-screw System For Quadrilateral Area (DAPSQ)

Most of pelvic and acetabulum fractures caused by high-energy injuries. With the development of modernization, the incidence of pelvic and acetabulum fractures showed a increasing trend year by year, the fatality rate and the forward disability rate of the injury with non-surgical treatment are very high. In recent years, with the development of the technology of open reduction and internal fixation and the community’s recognition of surgical treatment, the cure rate of the fractures improve constantly. Due to the deep anatomic site of the acetabulum fracture, the anatomical structure around the acetabulum is complex, the biomechanical structure of pelvic and acetabulum is special and the fracture forms are diversity, which bring some difficulties in surgical reduction and internal fixation of this injury in clinical. At present, there are a number of internal fixation methods could be used for pelvic and acetabulum fractures.Adopting a single approach with the characteristics of simple direct, safe and effective to fix has been the treatment goal of acetabulum fracture.Our department also has attempted to do it and carried on some exploration about it.Our department developed a kind of innovative Internal fixation system, which is dynamic anterior plate-screw system for quadrilateral area (DAPSQ, specially-shaped reconstruction plate),we treated the fractures that included the both-column acetabular fractures with anterior column injury serious, the transverse acetabular fractures with forward displacement, part of the anterior column acetabular combined half part of horizontal fractures using the reconstruction titanium plate combined with 3to5 trans-plateconical screws(SO-called quadrilateral screws)via the ilioinguinal approach after the fracture reducution. The Clinical efficacy of this Internal fixation system was satisfactory. With the high security, there is not screw entering into the hip. However, we had Suffered from some restrictions and been confused in clinical application of the internal fixation system, such as the acetabulum fracture involving the both-column with the contralateral unstable pelvic ring, it’s very difficult to deal with the fracture by the internal fixation system only, instead, it’s needed to fix the contralateral pelvic ring before, then adopting the internal fixation system, the related principle and mechanical properties is not clear. In order to study it further and improve the curative effect of treatment of pelvic acetabulum fracture in with the clinical application of fixation system, we chose the both-column acetabulum fractures as a representative of the complex acetabulum fracture which involving the double columns and the contralateral unstable pelvic ring, analysising the biomechanical stability of the fracture after internal fixation by Finite element simulation experiment, so that we can explore the mechanics principle of internal fixation system. The purpose of the study is to provide theoretical guidance for further clinical application and further optimization of the internal fixation system.Besides,we also follow up and observe the patients who accepted the treatment to evaluate its clinical efficacy futher.Part I Development and validation of a three-dimensional hexahedron mesh finite element model of the pelvis in standing positionObjective To develop and verify the validity of the three-dimensional hexahedral finite element model of the pelvis in standing position for applying it to clinical related biomechanics research by utilizing the finite element technology.Methods Choosing a healthy adult male volunteer, with the scope of pelvis from the fifth lumbar vertebra to the upper one third of femoral bone scanned with 0.5mm by multi-slices computerized tomography, we save the image data of the Pelvic area into CD with Dicom format. The three-dimensional hexahedron mesh finite element model of the pelvis in standing position was built by software of Mimics, ANSYS ICEM, Hypermesh and ABAQUS. Taking the plane of the upper end plate of first sacrum as the standard level, we constrainted the ischial tuberosity and limited the six degrees of freedom were limited. A uniformly distributed load of 600 N was applied in vertical direction on the upper lamina of S1 vertebrae to simulate the stresses on the pelvis in standing position and to verify the validity of the pelvis model.Results Developed a anatomic detailed three-dimensional hexahedral finite element model of the pelvis in standing position, the model was consisted of 88388 nodes and 86444 elements. The biomechanics characteristics of stress and strain of the Model which under the physiological load can reflect the characteristic of pelvis, The calculation results and stress distribution coincide with the results of the published literature data.Conclusion The newly developed three-dimensional hexahedral finite element model of pelvis in standing position has high veracity and is able to reflect the anatomy structure and mechanical properties of normal pelvic of human body objectively. The model could be used for pre-clinical biomechanics study about craniocervical region.Part II The finite element analysis of both-column fractures with the unstable contralateral anterior pelvic ring of acetabulum fixed by dynamic anterior plate-screw system for quadrilateral area (DAPSQ)Objective To explore biomechanical stability of the acetabulum fractures fixed by dynamic anterior plate-screw system for quadrilateral area when the contralateral pelvic ring was unstable.Methods Using the developed and validated finite element model of normal human body pelvic in standing position, we,according to the classification of Judet-Letournel in acetabulum fractures, simulated the type of single both-column fractures and the both-column fractures with the unstable contralateral anterior pelvic ring of acetabulum. We built three fracture models on the basis of the finite element model of normal human body pelvic in standing position:A model:No contralateral pubic ramus fracture; B model:Contralateral pubic ramus fracture titanium not plate fixation; C model:Contralateral pubic ramus fracture plate fixation. Then, the same physiological load was exerted on different model respectively. At the end, the none-line solution was analyzed, analysis of the stress and displacement in model.Results After analysising and comparing the lateral and longitudinal displacement and the stress nephogram of the three different fracture models, we found that the transverse and longitudinal displacement is small with dynamic anterior plate-screw system for quadrilateral area internal fixation when the pelvic ring is stable, which is according with standard of reset, the stress of fracture model was well distributed, there is no obvious phenomenon of high concentration.The fixed intensity bigger, the fixed pelvis is more stable. But when accompanied by unstable pelvic ring, the vertical and horizontal displacement of the fracture line show the result B>C>A.Conclusion The contralateral pelvic ring must be stable when we treat of the both-column acetabular fractures fixed by dynamic anterior plate-screw system for quadrilateral area.