| MeaningIn case of road traffic accident, the lower limb injury was commonly occurred in pedestrian-vehicle collision. As the largest and most complicated joint, knee injury was not rare. The reappearance of the injury process and the deduction of the injury formation are the difficult problems for common forensic investigations. Especially, the case studies were required to analyze the relationship between existed disease and caused wound as an fatal reason objectively.The purpose of this study is to provide some references of injury formation, injury mechanism and reappearance of collision process for forensic expert during court trail.To combine the medical image technology with finite element analysis under a construction of a virtual human model close to the real, to simulate the collision process through the virtual model of human body. After a comparison of human biomechanical results include deformation, stress and strain in collision, can be helpful for forensic experts to analysis human body injury effectively.In China, the research of human injury are mainly focused on the clinical operation and rehab treatment, there is lack of study about the knee injury for mechanical violence, and its participation of soft tissues during the injury process. On the other hand, there are still many researches using simply knee model without skin, surrounded muscles, solid ligament and proper material properties. Moreover, measurement of biomechanical data of knee joint from corpse was different from the living one.In case of foreign country, although there are many improved human knee finite element model include bony structure, main ligaments and meniscus, some of them are still not pertinent to express physiological complexity.Therefore, to construct the finite element model in depth by referring the physical environment objectively, in order to obtain an more accurate result with a better injury presentation. This was useful for forensic experts to infer the injury mechanism at limited time.Method1. Establishment of3D finite element model of human knee joint.To collect DICOM data form a male volunteer without knee disorder in supine position under CT equipment, scanning from distal femur to tibia plateau in extend state, there are total262slices and saved as DICOM format. The above DICOM images were then imported to Mimics15.0modeling software, the bony and soft tissues were sketched, the knee components were exported as STL format after smoothed.To import the STL components into the3-matic6.1CAD editing software for ligaments optimization, the position, thickness and length were checked by comparing with the MRI data. Auto-fix function was used to check out the triangular mesh in order to reduce the calculation errors and satisfied the requirement of meshing software.To transfer the refined components to the ICEM12.0meshing software to mesh up the knee parts. Using the automatic meshing function at the quality of0.45, the mesh quality was improved by rechecking. The knee parts in INP format were then exported to the analytic software.The fined knee parts were gathered in ABAQUS analytic software to set up the material proprieties, assembly, loading, contact interfaces and boundary condition. To set up the above configuration according to the published literature and physical measures. The calculation was stopped to repeat until the results had convergenced.2. Verification of a3D finite element model of human knee jointThe three point bending test, which based on the method of literature, both ends of bone were fixed, a loading of one end was6000N, the impinger diameter was12mm, the collision direction was perpendicular to the bone axis under400N loading. No friction was applied between the bones and impinger during the static test, in order to eliminate the effect of strain rate and inertia; the results were collected and checked by comparing with reported literature to verify the injury possibility.The knee joint drawer test, axial pressure was imposed at the upper end of femur at1150N in according with the reference; a134N force was exerted at the distal femur horizontally. A forward movement of femur was no more than4.75mm, and the opposite were not more than5mm. Frictionless is defined among the contact surfaces; the results were collected and checked by comparing with literature to verify the stability of model.3. Application of3D finite element model of human knee joint in traffic accidentThe knee injury simulation in lateral direction was operated under the finite element analyzing software, ABAQUS, the lateral impact speed were set up as10m/s,20m/s,40m/s respectively. These results of stress, strain and collision time were collected from several stimulations and checked by comparing with the limit stress (36.4M Pa) and limit strain (0.15) from reported literature to deduce the possibility and degree of soft-tissue injury for pedestrians.The knee injury simulation in flexion situation for rider, the verified knee model was imported to ABAQUS analyzing software, the lower part of tibia, fibula and outer-muscles were fixed, body weight and150N horizontal force were imposed to the upper part of femur, These results of stress, strain and collision time were collected from several stimulation and checked by comparing with the normal stress and strain of reported literature to deduce the possibility of soft-tissue injury.Result1. The established finite element model of the human knee joint was consisted of58448nodes and269508tetrahedral units. The model was included the knee bones, main ligaments, meniscus and the surrounding muscles, the physiological complexity of human was partly exhibited. Numerous mesh, compacted contact-pairs and checking during process were proved in the preliminary experiment, continues of stress distribution and steadily result was provided by high quality and quantity of tetrahedral mesh. Penetration of mesh can be avoid through contact-pairs setting. The checking of model can provide an more accrue result.2. For the result of three point bending verification, fracture results were closed to that of published literature. For the result of drawer verification, the result of stress for most ligaments was similar with the reported literature. The verification results indicated the reliability of finite element knee model.3. For the result of the collision simulation for human knee joint model in traffic accidents, the surrounded muscle play an important role in low-speed collisions, as an function of protecting the internal tissues. When the speed was higher than20m/s, the risk of injury for partial ligaments and meniscus began to increase. Within the high speed collision as40m/s, ligaments and meniscus in knee were seriously damaged.4. For the result of the flexion simulation for human knee joint model in traffic accidents, the strain of knee flexion was similar with the reported literature. A deduction of soft-tissue injury possibility can be achieved by the different between flexion strain and collision strain.Conclusions1. This study successfully established a three-dimensional finite element model of human knee joint, which provides a research foundation for deducing the mechanism of knee joint injury and judgment of injury manner of forensic investigation in road traffic accidents.2. In this study, the similarity of verification results of soft-tissue in knee drawer test and bony structure in three-point-bending test with reported literatures, which demonstrated the effectiveness of the model.3. The result of simulations can objectively reflected the stress, strains and deformation of the injury process and the range of soft tissues injury. Therefore the changes of collision provided an deformation analysis, injury deduction and forensic evidence for investigation.4. Problems and prospects of the studyDue to the limitations of analysis software, output of ligament tension and contact force were absent, in case of simplified cartilage components, the interrupt of stress of meniscus from femur and tibia was little, however, the results of contact force measurement will be affected. So the further improvement of research technology and software optimization, more flexion angles and collision velocities from the static finite element analysis to the dynamic finite element analysis in researchCreative innovationThis research had the following advantages:1. In the present study the knee joint of human vulnerability, the adding of surrounding muscles could be used to understand the role of surrounding muscle in collision. 2. To improve the quality standard of mesh could provide a more accurate simulation results;3. Medial collateral ligament was easily damaged in reported literatures, and our research discovered the lateral collateral ligament was far easier than the medial collateral ligament. |
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