Biomechanical Analysis Of The Lumbosacral Segment Of The Spine Using A Three-Dimensional Finite Element Model

Objective: To find the method of exact three-dimensional finite element model (FE Model) construction of the lumbosacral segment of the spine, discuss the stress variation on the segment in different postures and study the biomechanical pathologic mechanism of the relative diseases.Methods: To select a healthy adult volunteer without disease or deformity through radiological and physical examination. Spiro-CT scanning of his lumbosacral segment was then operated. The data of CT images can be obtained and output with DICOM format. The CT images were processed by Mimics to become 3-D entities of lumbosacral segment. The 3-D entities were meshed to tetrahedron by finite element analysis software MSC Patran. The discs, ligaments and zygapophysial joints can also been made 3-D entities. Different material was assigned different mechanical parameters, and a three-dimensional finite element model of lumbosacral segment was constructed. 500N preload was given on the top of the L5 to simulate standing positions, and 15N·m moments of forces were given on top of the L5 to stimulate the antiflexion, extension, lateroflexion and contortion movements. Then evaluate the stress distribution and transmission, calculate the average stiffness of the FE Model.Results: The constructed FE Model of lumbosacral segment consisted of 51,072 solid units, 396 linear units which consist of 44 ligament units, 26 joint units and 324 annulus units. There are 12,934 nodes in total and included geometrical, contact non-lineadties. Under flexion or extension, the stress concentrates on the posterior part of the L5 vertebra; both the isthmus and zygapophysial joints have heavy loads. Under lateroflexion, stress concentrates on the ipsilateral isthmus, while under contortion; stress concentrates on the opposite side. The bilateral wings of the sacrum distribute the majority of the stress on the upright and antiflexion position. Under all kinds of motions, the stress concentrates on the outer fibers of annulus fibrosus, and the posterolateral side is the most common place of stress concentration. Heavy stress was observed on the annulus on the position of lateroflexion and extension. The posterolateral side is also the most common place of disc displacement. The average stiffness of the FE Model under antiflexion, extension, lateroflexion and contortion movements are 2.10 N·m/°, 3.12N·m/°, 3.07 N·m/°and 7.80 N·m/°alternatively.Conclusion: The constructed FE Model of lumbosacral segment objectively reflects real anatomical outline and biomechanical behavior of the segment of the spine. It helps us better know the biomechanism of the diseases on this area. The model we constructed can be used for further biomechanical research.