BIOMECHANICAL RESPONSE OF A FUNCTIONAL SPINE UNIT UNDER VARIOUS LOADING CONDITIONS: A VISCOELASTIC FINITE ELEMENT APPROACH

摘要

Biomechanical and epidemiologic studies state that recreational activity and industrial work, embodying static work postures, physically heavy tasks, frequent bending, and twisting motions, lifting and sudden loading incidents are highly related to low back pain disorders. In order to provide a comprehensive understanding of the low back pain under severe and traumatic static and dynamic loading conditions, the finite element (FE) technique is widely used as a computational method to model, simulate and analyse the behaviour of the spinal segments in the lumbar spine, which are much more difficult with in vitro and in vivo experimental studies. Intervertebral discs, having many other functions, support a huge extent of the compressive loadings the trunk is subjected to. The results of the FE analyses can be employed to understand the injury mechanisms occurring in and about the intervertebral discs, providing stress and strain distributions, and to aid the therapists in selecting the type of treatment for low back pain, and in developing guidelines for industrial safety. In the literature, several studies have been reported regarding finite element analysis of the lumbar spine and the segments of the lumbar spine such as L2-L3 level functional spine unit. In his detailed study, Shirazi-Adl developed and validated a three dimensional FE model of the whole ligamentous lumbar spine (LI-SI) to investigate the behaviour of the components under flexion, extension, and lateral moments. Similarly, Lavaste et al. [2] constructed a 3-D mechanical model of the whole lumbar spine, using radiographs of lumbar vertebrae. There are some other researches on the lumbar spine, which concentrate on the functional spine units, such as L2-L3 or L3-L4 motion segments, rather than the whole detailed geometry. These studies involve simplified representations of the vertebral bodies and the disc, without modelling the rest of the vertebrae parts such as pedicles, facet joints and processes. In all of these studies, the main objective is investigating intervertebral discs under several loading conditions, which are modelled as elastic, viscoelastic or poroelastic entities.