Research On Thoracolumbar Biomechanical Modelling And Application

Human being is a very complex system, due to the differences between individuals, diversity of human musculoskeletal system and limitation of experiment condition in-vivo, it is very difficult to develop researches on human body biomechanical characteristics. At the same time, the demand of living quality improves with the improvement of living standard. How to correct some deformility diseases and how to effective evaluate the medicine implants are becoming an important task for relative biomedical researchers.This dissertation is based on the key project"mechanical virtual human of China"supported by National Natural Science Foundation, and two projects cooperated with RenJi Hospital.and ShangHai RuiZhi medical divice Co. Ltd, respectively. First, the 3D geometrical model and biomechanical model of human thoracolumbar"skeleton-muscle"system were estalished. Then, bending lift was chosed as the typical movement. The muscle forces of relative movement muscles were predicted. The muscle forces were assigned as the broundary condition, the stress distribution of vertebral bone and vertebral disk, the deformilty curve of spinal center, the principal stress of vertebrae and the force of ligaments were analyzed. The individualized brace was designed and its biomechanical characteristics were studied for adolescent idiopathic scoliosis patient. The model of L4-L5 functional element was chosed from"mechanical visiual human of China"model database. The intervertebral disk was replaced by the new type artificial disk. The biomechanical characteristics of this new artificial disk were evaluated. The main contents are listed as following:1. The modeling of the human thoracolumbar musculoskeletal system was established based on cryosectional images and CT data. In order to extract the outline of the bone and muscle as possible as precision, we utilized the image segmentation and B-spline curve approximation, to obtain the outline information accurately. The established anatomical model includes 12 thoracal bones (T1-T12), 12 pairs rib bones and sternum, 5 lumbar bones (L1-L5) sacrum, interbertebral disks and the origin and insertion points of total 179 muslce fascicles relative with bending lift such as abodominal and dorsal muscle.2. The line model of 179 muscle fascicles relative with bending lift was constructed under the direction of anatomical doctor. With the NDI motion capture system to obtain the motion information of the spine, using the surface EMG measurement system to obtain the muscle EMG signal. The muscle forces in the movement were predicted by use of quadratic programming method, which would be used as the boundary condition in the finite element anlysis. Moreover, the predicted muscle results were testified with EMG,which showed the results have a high similarity with the real.3. According to relationship of the CT Hounsfield value and Young's modulus, the mean Young's modulus of vertebrae cancellous bone and posterior element were calucated. The annulus fibrosis model was simplified by assigned an equivalent material property. The stress distribution of cortical bone, cancellous bone, nucleus pulposus, annulus fibrosis, the muscle force of ligament, the principal stress distribution and the change of spinal center curve were analyzed.4. Based on 3D CT scanned data of a scoliosis patient, an accurate finite element model including thoracic, lumbar, sacrum and pelvis was developed, the individualized scoliosis brace was constructed based on the T-L-S-P FE model and their correction effect on three different strap tensions were investigated. The results showed that the individual brace treatment had better correction efficiency than other braces in coronal plane and had no inverse effect in sagittal plane. The research provides an available method for the design of individualized brace, which could help improve the correction efficiency for idiopathic scoliosis.5. The model of L4-L5 functional element was chosed from the"mechanical visiual human of China"model database. The intervertebra disk was replaced with the new type artificial disk. Its biomechanical properties were analyzed. The conclusion is that the new artificial disk can reconstructe the height of intervertebral disk and demand the motion function of intervetral disk. At the same time, it would result in stress changes on the verbetrae bone and facet joint. Therefore, its long-term effects should be investigated through further follow-up observation.The 3D geometrical model, kinematics model and finite element model of human thoracolumbar can be widely used to biomechanical anlysis, such as used to analyze the artificial disk biomechanical characteristics in vitro. The study on individualized brace of adolescent idiopathic scoliosis can be used to guide the orthosis designer to design and manufacture more efficient correction brace and improve clinical efficiency.