PSI - Issue 28

Hassan Mansour Raheem et al. / Procedia Structural Integrity 28 (2020) 1727–1732 Hassan Mansour Raheem et al. / Structural Integrity Procedia 00 (2019) 000–000

1731

5

Figure 5 shows the disc with partial removal of the nucleus pulposus. An opposite trend then the disc without nucleus pulposus can also be seen. The bulging in both areas is outwards. The interpretation of this behavior is due to increasing the pressure at the central part of the annulus, i.e. the nucleus with higher values of the bulging in both directions x, and y-direction, compared with the disc without nucleus pulposus. However, Meakin et al. study (Meakin et al. 2001) reported that partial removing the nucleus pulposus leads to that the bulging in the annulus becomes inward. This discrepancy because they removed a portion of the nucleus close to the posterior region, but in this study, the nucleus pulposus was modeled as 95 % filling the gap and it was distributed evenly in the vacancy.

Fig. 5. The bulging distribution in the disc with 95% of 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. Figure 6 shows the bulging response of the model for the intact disc, i.e. the disc with 100% of the nucleus pulposus. The disc exhibits a slightly similar response to that of the partial removal of the nucleus pulposus (Fig. 5). Both posterior and posterolateral regions bulge outwards. This response is in line with the reported results of Shirazi et al. study (Shirazi-Adl et al. 1984), where the bulging displacement of the posterior region is greater than other regions as shown in Fig. 6b. It is also that the bulging values for the intact disc are higher than of these for the disc without and with partial removal of the nucleus pulposus.

Fig. 6. The bulging at the posterior (solid line) and posterolateral (dotted line) regions of the disc with nucleus pulposus under axial compression loads (a) the bulging in the X-axis; (b) bulging in the Y-axis. 4. Conclusion This study provides a simple three-dimensional FE model that resembles the response of the functional spinal unit of the human lumbar region. The results show that the disc condition significantly affects the bulging in the disc. The posterior region bulges inwards for the disc without nucleus pulposus, while it bulges outwards for the intact and