PSI - Issue 28

Hassan Mansour Raheem et al. / Procedia Structural Integrity 28 (2020) 1727–1732 Hassan Mansour Raheem et al. / Structural Integrity Procedia 00 (2020) 000–000

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Further validation on the model has carried out by comparing the stress distribution in the annulus fibrosus of the disc in two cases: without and with nucleus pulposus with Meakin et al. study (Fig. 3b) (Meakin, Reid, and Hukins 2001) as shown in Fig. 3. The comparison shows closely matches with literature data (Meakin et al. 2001). This approach provides an overall validation of the model.

Fig. 3. Stress distribution in the disc with (top) and without nucleus pulposus (bottom) (a) the model, the solid line square represents the area of interest; (b) Meakin et al. study (Meakin et al. 2001) 3. Results and discussion In this study, a three-dimensional finite element (FE) model simulates the human functional spinal unit of the lumbar region under axial compression loads is built using ANSYS software. The model is reported without the posterior elements because they do not have significant effects on the results (Seroussi et al. 1989). The material properties of the annulus and nuclease are assumed to be linear elastic. The structure of the annulus is also modeled as a homogeneous material without fibrin. Figure 4 shows a typical response of the model without the nucleus pulposus. It can be seen that the outer margin of the annulus fibrosus at the posterior region bulges outwards (Fig. 4a), while the inner margin bulges inwards (Fig. 4b). This trend of bulging could be attributed to the geometry of the disc. However, it is important to understand the behavior of the disc without nuclease pulposus to prevent the damage of the surrounded area of the disc. These results agree with the reported results of Shirazi et al. study (Shirazi-Adl, Shrivastava, and Ahmed 1984). Note that the positive direction of the coordinate axis in Fig. 3 and the related values of the bulging. Generally, the negative values (Fig. 4a) represent inward bulging, whereas the positive values (Fig. 4b) represent the outward bulging of the disc.

Fig. 4. The bulging distribution in the disc without nucleus pulposus at the posterior (solid box) and posterolateral (dotted box) regions, (a) directional bulging in the X-axis; (b) directional bulging in the Y-axis.