| BACKGROUNDWith the rise of biological fixation for school in the early1990s, A variety of innovative fracture internal fixation techniques and equipment have been researched and widely applied. Locking compression plate is one of them. which is a new kind of internal fixation system developed on the basis of regular internal fixation plate In2001..LCP is thought to be the ideal fixation material for biological osteosynthesis.LCP was widely used in minimally invasive plate osteosynthesis in recent years, and was used in the treatment of long bone fracture within the form of fixed bracket. At present, most of the domestic and foreign scholars in the study of extremities fractures treated by locking compression plate is concentrated in the retrospective study of clinical application and clinical curative effect. There were also many clinical comparative study focus on the LCP、intramedullary nailing and anatomy compression plate. And still a few scholars have conducted on biomechanical study with animals and humen body specimen. Although the locking compression plate was widely used in the worldwide,and the mechanics characteristics of LCP itself is quite clear, But the biomechanical study of the locking compression plate applied to the humen body fracture was still lacking, the guiding significance data of biomechanical analysis to the Clinical application was insufficiency.As a kind of scientific research methods, three-dimensional finite element analysis (FEA) was widely used in the industrial research field in recent years, and Was introduced to the medical research field by the domestic and the foreign scholars who have achieved some results with the aid of the FEA. In the medical field, the biomechanical characteristics of the human body has been further researched by means of the FEA. Although the human body is a very complicated structure, the modeling characters of the finite element software can still build three-dimensional structure model of the human body, and assigned the biomechanical characteristics of the material to this model. The FEA software can also create virtual3d experiment specimens based on the computer, and apply thoes function such as the geometric constraint, the fixed load, the impact load, the temperature characteristic and the experimental conditions etc to this virtual3d experiment specimens. The FEA software can simulate bending, torsion, tension, fatigue resistance and three-point bending mechanics experimental conditions, and gain the biomechanical indexes of the virtual3d model which is similar to the human body experiment specimens by solving. For instance, the biomechanical indexes including the stiffness, the structure deformation of any parts, the stress/strain distribution changes, the internal energy transformation, the ultimate strength etc. Compared with the traditional experimental methods,the FEA has the incomparable advantage, which can copy out countless experimental specimens according to the experiment designe, and each test specimen can be combined or split to countless times in the computer without any damage. Not only the physiological information of the normal human body can be gain by the virtual3d experiment specimens, but also the pathological state of the human body can be simulated.Based on various virtues above, the FEA has gradually access to the medical field’s attention for the past few years, especially obtained the orthopedic clinical attention’s focus. The FEA has been widely used for the biomechanical analysis of the human body fracture internal fixation modelsin clinical studies. After reading a large number of literature, I found that prior biomechanical study of the steel plat are limited to the static state, for those study under the move Status has not yet been reported. Based on the status quo, the author taking one of the most common type of human body fracture——the tibia fractures as the study subject combined with the clinical practical experience. The virtual3d finite element model of the normal adult tibiofibula and ankle was established by the3d reconstruction software Mimics10.01, carries on the HyperMesh and assemble with the locking compression plate in the finite element analysis software Ansys12.0, the virtual3d finite element model of various tibia fracture fixed by the locking compression plate was built after thoes treatment measures above.The corresponding stress distribution data of the virtual3d finite element model under different gait can be drawn after a series of pressure loading and mechanics analysis, and carry on further discussion of the stress distribution of different tibia fracture under various movement gait.OBJECTIVE1. To explore the stress distribution of different tibial shaft fracture fixed by LCP under Static gait through three-dimensional finite element analysis.2. To explore the stress distribution of different tibial shaft fractures fixed by locking compression plate under different movement gaits through three-dimensional finite element analysis.METHODS1. ObjectOne healthy male volunteer,25years old, height170cm, weight60kg. There was no bone destruction in the right lower limb of the volunteer, such as fracture,monstrosity, osteoporosis and tumor etc, which were confirmed by the X-ray examination. The volunteer’s height and weight conforms to the standard normal distribution of the normal chinese. The volunteer was told of the experimental scheme and agree to take part in the test.2. MaterialsTitanium alloy locking compression plate with8hole; Provided by Changzhou orthmed medical instrument co., LTD.3. MethodsCT scan was performed to obtain the thin layer scanning image of normal adult tibiofibula and foot; three-dimensional models were established by relative software, and then transverse, oblique, spiral, comminuted fractures were imitated on the models and combined with the locking plate to generate the experimental models. The models in each group were subjected to the same axial and slant compression load of600N. The stress distribution of the models under different motion state and different load was analyzed with software Ansys12.0.3.1Data Collection The CT scanner used in this experiment belong to the second people’s hospital of guangdong province. The CT scanner used in this experiment belong to the second people’s hospital of guangdong province. The volunteers take supine position; The CT scanner step by step scanning from the foot bottom to the knee above; Totally663layer two-dimensional CT images were obtained, and0.45mm thickness per image; The images data was stored in DICOM format. The DICOM format image of locking compression plate and screw were obtained by the same way. The CT scan parameters:tube voltage120kV, tube current100mA.3.2Finite element model of the tibia:CT scan data of the tibil was imported into the Mimics10.01software. The two-dimensional spatial orientation was established. The threshold value of the bone in CT scanning image is between226-2311. By using the threshold range can help to distinguish the bones and other soft tissue section. Regional growth function of Mimics10.01software was used for the image segmentation filling, and the tibiofibula geometric model generating. the STL format data was import into the Geomagic Studio10.0(the Raindrop Geomagic companies, USA) to establish the spatial topology information of the geometric model.By creating the characteristics of the joint surface boundary to define the model boundary condition, Segment the data, build the grid mesh, and finally complete the curved surface fitting. The combining NURBS (Non-Uniform Rational B-Splines, NURBS) surface data was imported into the reverse engineering software UG in the format of Iges. Respectively simulate the transverse, oblique, crushing, spiral fracture entity model of the tibia in the middle section.The stitching function of the UG software can used to assemble the tibia fracture model with the eight hole locking compression plate model together; and generate the entity model. Finally the three-dimensional entity model was leading into the ANSYS12.0software (The ANSYS corporation, USA), The software automatically carry on the grid tumble to the model, and carry on the mechanical analyses.3.3Load loading way:preestablish the static gait and the movement gait two kinds of boundary conditions, and carry on the axial compression loading separately to the assembled finite element model. Among the loading way, under the static gait, carry on the Load loading to the compound model in the standing weight-bearing position and the stepped inclined position. Under the movement gait, carry on the Load loading to the compound model in3direction of the push-off phase、the midstance phase and the heel-strike phase.Preestablish the angle of the tibia in the finite element model and the plumb line was Zero degrees under the the neutral phase. It’s means that the tibia was perpendicular to the horizontal plane. Preestablish the angle of the tibia in the finite element modeland the plumb line was24degrees under the heel-strike phase、the push-off phase and The stepped inclined position. It’s means that the tibia was tilt to the horizontal plane. Fixed the upper of the tibia in the model; Centered on the tibial plateau; The axial compression load loaded on each group was600N, and the stress direction through the axis of the tibial stem.3.4Finite element stress calculation:Input the load above into the ANSYS12.0software, and carry on the stress analysis to the composite system of the tibia and the locking plate under the static gait and the movement gait separately.3.5Main outcome measures:In the static gait, observed the stress concentrated area of the tibia and the locking plate in the the leaning and erect position. In the movement gait, observed the stress of the tibiofibula and the locking plate finite element model under the three different gait in each fracture model group.3.6Statistical analysis:The SPSS15.0statistical software (SPSS, companies in the United States) was used to carries on the analysis of variance to the data.RESULTSThe virtual three-dimensional finite element model of different types of tibia fracture fixed by locking compression plate was successfully established in the experiment. The load subjected to the model carry on in the FEA software; and the calculation measured by the finite element analysis software are as follows.The stress distribution of the steel plate the stress distribution of the locking compression plate in the tibial transverse, oblique and comminuted fractures from small to large was the midstance phase<the heel-strike phase<the push-off phase; the stress distribution of locking compression plate in the tibial spiral fracture group from small to large was the push-off phase<the midstance phase<the heel-strike phase. The stress distribution of the locking compression plate focused on the middle or edge of itself; Which presents the trend of focused on both ends, and scattered on the middle.The stress distribution of the tibia In the movement gait under axial compression load, the stress distribution of the tibia under the physiological state in four groups from small to large was heel-strike phase<push-off phase<midstance phase. In the movement gait unde the middle tibia fracture model, the stress distribution of tibia in each groups from small to large was heel-strike phase<midstance phase<push-off phase. As can be seen from the finite element stress distribution nephogram of the tibia, the stress distribution of the tibia focused on the proximal end above the fracture line and on the end under the fracture line. From the overall of the tibia, the stress distribution focused on both ends, and scattered on the middle. In the comminuted fracture group, the stress of the tibia and the plate have significant difference (P<0.05) with the othor three groups. while, the stress of the tibia and the plate in the tibial transverse, oblique and comminuted fractures was no significant difference.The stress distribution of the fibula In the movement gait under axial compression load, the stress distribution of the fibula under the physiological state in four groups from small to large was push-off phase<midstance phase<heel-strike phase. In the movement gait unde the tibia fracture model, the stress distribution of the fibula in each groups from small to large was push-off phase<midstance phase<heel-strike phase.CONCLUSIONThe study show that the stress distribution size and scope of the Tibia and plate in the different movement states are differant, there are also differences in the different fracture model.1. Under the static gait:the stress size change tendency of the tibia and steel in each group under the axial load was consistent; the stress size change tendency of the tibia and the steel plate in each group under the oblique load was instead; Under different load, the stress distribution of the steel plate was fragmented; the stress distribution of the tibia was focused on both ends, and scattered in the middle.2. Under the movement gait:the largest stress of the steel plate and tibia were in the push-off phase; Under the transformation process from the static to the movement, the stress of the tibia and the steel plate was gradually increasing; The stress distribution of the steel plate was focused on the middle, and scattered in both ends; The stress distribution of the tibia was focused on both ends, and scattered in the middle. |
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