# On the Finite Element Modeling of the Lumbar Spine: A Schematic Review
## 4 Discussion  
The present study involved a schematic literature review conducted to fully analyze the existing literature about FE modelling of the lumbar spine. This work involved number of different steps. First, a search was conducted through the Web of Science and Scopus databases in order to find the most relevant works, using specific keywords to identify the most innovative approaches. A laborious screening process followed, starting with the removal of duplicates, then further screening through additional keywords, title, and abstract. A total of 31 articles were included in the final review, each of which was exhaustively examined. The nature of the selected articles was assessed through the VosViewer software. Figure 2 demonstrates how most current investigations have focused on topics aligned with the database research concerning the following: the lumbar spine, FE analysis, computational analysis, spinal load, validation, etc. Network visualization was essential for verifying the relevance of the resulting database. It can be clearly seen that the obtained database suits the desired search parameters. Afterwards, the publication dates were analyzed. Figure 3 highlights the works in the source database, showing that they cover a wide temporal interval ranging from 1992 to 2022. This range allowed us to observe both the evolution and the consistency of computational modelling techniques of the lumbar spine over the years. The final step was the extraction of data from articles presented in this review. All articles were carefully examined in order to extract the researchers' choices in modelling the different parts of the considered anatomical area along with the numerical  
Figure 4: Different loading conditions: (**A**) imposed displacement, (**B**) compression follower force, (**C**) lateral bending, (**D**) extension and flexion moments. techniques used for the boundary conditions, loading conditions, and model validation process [14; 15; 21; 24; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62]. All of this information is included in Tables A1-A6. These tables show the modelling proposed by the different research groups, as well as their approaches to FE. The information was extracted separately in relation to the cortical bone, cancellous bone, posterior bone elements, cartilaginous endplates, annulus ground substance, annular collagen fibers, nucleus pulposus, ligaments, and follower load. Based on a careful analysis and data extraction process, the main models used by researchers were stratified and presented; see Table 2.  
Cortical bone and cancellous bone are the anatomical components that exhibit the most similar numerical approaches. Isotropic elastic modelling represents a good assumption, though modelling with transverse behaviour would be the best choice to simulate the unique characteristics of cortical bone and the trabecular architecture. Posterior bone segments can be schematized simply through linear elastic behavior, and is used by most researchers. The cartilaginous endplates can be schematized by linear elastic behavior or even as a hyperelastic Neo-Hookean material. The computational results obtained from Von Mises stress analysis or from verification of the component displacement allows for a certain homogeneity in the literature to be observed from the data obtained from simulations in relation to these models. The intervertebral disc is the most challenging to model because of its three different components, i.e., the nucleus pulposus, annular ground substance, and annular collagen fibers. Overall, the disc exhibits viscoelastic behaviour, which means that hyperelastic modelling is the most appropriate. Many different hyperelastic models are used for the annular ground substance and the nucleus pulposus; among the most common are the Mooney-Rivlin and Neo-Hookean models.