the nucleus pulpous of intervertebral disc effect on finite element modeling of spine

background: spine of an adult is made up of five areas that include 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, sacrum and finally coccyx. selecting appropriate assumptions for modeling and biological analysis of the spine components has a significant impact on the accuracy of results in biomechanical simulation for different modes. methods: in the present study, biomechanical analysis has been done on the spine by using finite element simulation. dimensional characteristics of an individual’s spine components are obtained, then the spine model as one-piece and intervertebral discs as two modes of one-piece and two-piece (annulus and nucleus section) in the form of two separate models is modeled. gravity caused by the weight of spine (gravity intensity of 9800 newton per square millimeters) was applied to the model and output of stress, displacement and changing the angle between the vertebrae of the spine has been obtained. results: the maximum displacement, stress and change of angle between the vertebrae in spine model with one-piece disc was 0.254 and 0.197 and -0.083 respectively, and for the model with two-piece disc is 0.399 and 0.205 and 0.021 respectively. conclusion: according to the results for examining the stress, there was no significant difference in choosing the assumption of two-piece or one-piece of the intervertebral disc, but results of the model analysis with assuming two pieces of the intervertebral disc is more appropriate in examining displacement and changing the angle between the vertebrae.