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The objective of this work is to study the effect of obesity on the intervertebral discs and provide system analysis of the spine between multiple configurations of people, and know the risks due to this eccentric load (Big Belly). The results show that in all three previous loadings (obese people), the distributions of stress and strain are high in both D1 and D10 intervertebral discs. This shows that the distance between the point of load application and the spine axis has an important role in solicitation increasing and therefore its deformation: as main conclusion is that the concentration of the mass of stomach fat is a risk factor that leads to pain problems, deformation and herniated disc.

The prediction of the mechanical behavior of the spine system is one of the major problems of biomechanics [

The spine or rachis consists of a movable column of 24 free vertebrae and a fixed column formed of fused vertebrae: the sacrum and coccyx (

The degeneration of the lumbar discs is definitely related to BMI; overweight and obesity are associated with a higher risk of problems of the spine. The MRI study [

Rheumatism, the Journal of the American College of Rheumatology, alerts on this effect of overweight in the development of degenerative disc disease and back pain and then herniated disc (

The term obesity is defined as an eccentric load (

The objective of this work is to provide an analysis between a geometric configuration of the spine system, to find the effect of eccentric loads on the latter and mainly on the inter vertebral discs by analyzing the stress distribution in this system using a 3D numerical simulation, based on the principles of the finite element method. The analysis of biomechanical problems includes several steps.

The first is to study the form to define the geometrical configuration of the object, which allows the reconstitution of the vertebra, the ligament and bone using CAD programs.

The result is a 3D geometric model including these three components will then be prepared for use in finite element analyzes for the study of stresses and deformations distribution in the system.

The Steps to the execution of the 3D vertebra model (

a) Draw cortical bone that is the upper hinge and the lower hinge, and make the smoothing; this gives a solid body called the vertebral body.

b) Secondly, draw the posterior arch (blade + the pedicle) with the spinousprocess.

c) Finally we draw the transverse process.

The simulation of the disc degeneration is based on a finite element model of the healthy spine.

In static loading conditions, the model of the reconstructed spine is used in an analysis for studying the role of the inter vertebral discs and the stress distribution in these disks as well as its supporting structures. The spine is reconstructed in 3D to study the system dimensions (IVD-ligament-bone) (

In order to define the boundary conditions, restriction on movements of translation and rotation of the spine has been applied in the lower plane, and defined as having zero displacements. Several charges in the anterior direction were applied as follows:

The application of the load on the upper side of the thoracic vertebra TH1.

The fixed part applied to the body of the sacrum.

The interfaces between the different components of the system of the spine, the cortical bone, the inter vertebral disk and ligament are treated as perfectly bonded interfaces (

The selection of constitutive equations of the vertebral bone is defined as the part of the bone which carries the inter vertebral disc, composed of cortical bone, cancellous bone, the posterior arch, with a Young’s modulus of about 12,000 MPa. It is recognized that cortical bone: has: better load capacity than the cancellous bone: cortical bone is considered as an isotropic material, and homogeneous linear elastic.

The behavior of intertransverse ligament and inter-spinous ligament is nonlinear viscoelastic as in previous studies [

ANSYS WORKBENCH software was used for analyzing this geometry and generate the most suitable mesh. For the studied behavior, we used tetrahedral elements, type Solid187 conforming to defined parametric surfaces (

The material properties of the spine components were selected after a careful review of the published literature (

The complete model of the spine (

The posterior arch was modeled with tetrahedral elements to 10 nodes contains (2,377,091 element, 3,440,842 nodes), the nucleus pulposus in the annulus fibrosus were modeled with tetrahedral type elements 10 nodes (504,657 element 717,205 nodes), the annulus fibrosus were modeled with elements of type tetrahedral to 10

Authors | бr (N/mm^{2}) |
---|---|

BROWN (axiale) | 1.4 |

GALANTE (horizontale) | 3.5 ± 0.3 |

GALANTE (sens fibre) | 10.7 ± 0.9 |

WU | 3.7 |

Material | Young modulus (MPa) | Poisson coefficient | References |
---|---|---|---|

Cortical bone | 12,000 | 0.3 | [ |

Cancellous bone | 100 | 0.2 | [ |

Posterior bone | 3500 | 0.25 | [ |

Cartilage endplates | 12,000 | 0.3 | [ |

Annulus ground substance | 4.2 | 0.45 | [ |

Nucleus pulposus | 1 | 0.499 | [ |

Anterior longitudinal ligament | 20 | 0.3 | [ |

Posterior longitudinal ligament | 20 | 0.3 | [ |

Ligamentum flavum | 19.50 | 0.3 | [ |

Intertransverse ligament | 58.7 | 0.3 | [ |

Inter-spinous ligament | 11.6 | 0.3 | [ |

Supra-spinous ligament | 15 | 0.3 | [ |

Capsular ligament | 32.9 | 0.3 | [ |

nodes (1,434,546 element , 2,059,247 nodes). The gelatinous cartilage modeled with a tetrahedral element to 10 nodes (912,759 elements, 1,431,242 nodes). Finally the different types of ligaments generated by a tetrahedral mesh to 10 nodes (

The diagram in (

The length of the spine (thoracic + lumbar) is 72 cm and the distance between the specific weights of the belly which is the point of application of the load and the axis of the vertebral column (20 cm). For boundary conditions, the sacrum is fixed. (Embedding the sacrum (

We propose in this section to draw up a detailed study of Von Mises distributions constraints and deformations in the intervertebral discs as a function of supported loads.

The distance between the center of gravity of the belly and the axis of the vertebral column is between (30 cm/50 cm), the pressure load P is applied on the thoracic vertebra TH1.

To define the boundary conditions, restriction on movements of translation and rotation of the spine has been applied including frontal plane and defined as having zero displacements on the sacrum see

Consider the example of an anterior load (obese person), the colors represent the Von Mises stresses experienced by 17 intervertebral discs, blue represents the minimum stress and the red represents the maximum stress.

A load applied to the upper surface of the TH1 thoracic vertebra of the spinal column causes a high concentration of maximum Von Mises stresses in the anterior portion of the two discs D1 and D10 (red section) this is mentioned in

Moreover, the Von Mises stresses are minimal at the posterior part of the two intervertebral discs D1, D10 (blue contour) see

Component | Nodes | Elements | Thickness |
---|---|---|---|

Cortical bone | 5,132,199 | 3,585,646 | 1 mm |

Cancellous bone | 3,471,929 | 2,496,448 | 1 mm |

Posterior bone | 3,440,842 | 2,377,091 | 1 mm |

Cartilage endplates | 1,431,242 | 912,759 | 1 mm |

Annulus ground substance | 2,059,247 | 1,434,546 | 1 mm |

Nucleus pulposus | 717,205 | 504,657 | 1 mm |

Anterior longitudinal ligament | 227,078 | 128,365 | 1 mm |

Posterior longitudinal ligament | 158,748 | 92,426 | 1 mm |

Ligamentum flavum | 30,226 | 13,447 | 1 mm |

Transverse ligament | 285,328 | 131,648 | 1 mm |

Inter-spinous ligament | 28,968 | 13,158 | 1 mm |

Supra-spinous ligament | 17,833 | 8279 | 1 mm |

Capsular ligament | 51,816 | 24,072 | 1 mm |

Total | 17,150,901 | 11,762,783 | 1 mm |

Consider the example of an anterior load (obese person), the colors represent the Von Mises stresses experienced by 17 intervertebral discs, blue represents the minimum stress and the red represents the maximum stress.

We see in

Regarding the deformations Von Mises, we notice that the values are greatest in the two intervertebral discs D1, D10 of 3.86, 3.788 for a load of 16.55 kg obesity and 4.934, 4.393 for an obesity load 19.88 kg and 7.506, 6.718 for an obesity load 29.85 kg compared to other discs of the vertebral column (

In sum, we concluded for the three cases of anterior load (obese persons) (

Von Mises stresses are the highest in intervertebral discs and are concentrated in the disk D1, in contact with the L5 vertebra and the sacrum;

The authors extend their appreciation to the Director of Scientific Research at LaBPS for funding the work through the Biomechanics Research Group.

SamirZahaf,BensmaineMansouri,A.Belarbi,ZitouniAzari, (2015) Obesity Effect on the Spine. Advances in Bioscience and Biotechnology,06,556-571. doi: 10.4236/abb.2015.68059