The Effect of the Eccentric Loading on the Components of the 1 Spine 2

The objective of this work is to study the effect of the backpack on the components of the 8 spine system of a child, know the effect of an eccentric load on the intervertebral discs, the 9 creating a 3D model of the spine of child of 80 kg overall weight under the effect of three 10 eccentric load (P2, P3, P4) plus P1 compression load and calculated by the element method 11 ends, For the boundary conditions we fixed the sacrum (Embedding the sacrum). We propose 12 in this section to draw up a comprehensive study of the distributions of stresses and normal 13 elastic strain of Von Mises in the intervertebral discs based on loads supported.


MATERIAL AND METHODS
2.5 kg ... we're off!! It is between 8 and 15 years back is the most fragile, and scientific studies have demonstrated 45 imaging (MRI), the risk of joint damage and intervertebral disc are real [5]. 46 Yet the official circular of 2008 National Education clearly advocates that the weight of the backpack should not exceed 10% of the weight of the child, either primary, about 2.5 kg ... we're off!! It is between 8 and 15 years 48 back is the most fragile, and scientific studies have demonstrated imaging (MRI), the risk of joint damage and 49 intervertebral disc are real [5]. 50 During this period of school age, the spine of children is particularly rough ride. With their school bags too 51 heavy, students are real porter, causing stiffness and pain, which are themselves a source of bad posture on often 52 inadequate seating. 53 It is in this context daily, as well as family education, the accumulation, repetition of these situations will 54 cause joint damage, common causes such as scoliosis. This explains the fact that 67% of students suffer from 55 muscle tension, 50% of back pain, 24% falling asleep during classes and 15% of pain in the shoulders [5]. The 56 schoolbag defined as an eccentric load \" (Fig. ??) \", the load represented by the mass (P4), in other words, this 57 load created a moment of posterior bending which tends to bend the spine and causes a problem called lumbar 58 disc herniation is the most common cause of low back pain. The MRI study [6], alerts of this overweight effect 59 in the development of degenerative disc disease, back pain and then herniated disc \» (Fig. ??) \". 60 We propose in this work to draw up a comprehensive study of stresses and strains in the spinal discs

77
The objective of this study was to investigate the effects induced by an eccentric load of the backpack on the 78 back of a child, know the effect of an eccentric load on the intervertebral discs, cortical bone, cancellous bone, 79 posterior bone, sacrum, basin, created a 3D model of spine, the total mass of person standing of specific global 80 80kg under the effect of three eccentric loads (p2, p3, p4) plus a p1 compression load and calculated by the finit 81 element method, the boundary conditions we fixed the sacrum (incorporation of the sacrum) see \" (Fig. ??) \".

82
The analysis of biomechanical problems includes several steps.

83
The first is to study the form to define the geometrical configuration of the object, which allows the 84 reconstitution of the vertebra, the ligament and bone using CAD programs.

85
The result is a 3D geometric model including these three components will then be prepared for use in finite 86 element analyzes for the study of stresses and strains distribution in the system.

87
The steps for the execution of the 3D vertebra model \" (  with a Young's modulus of about 12000 MPa. It is well known that cortical bone has better load capacity than 112 the cancellous bone. Cortical bone is considered as an isotropic material, and homogeneous linear elastic. Table   113 ?? shows the tensile strength of the structure annulus fibrosis according to different authors. These materials are 114 anisotropic and non-linear elastic.

115
The behavior of inter-transverse ligament and inter-spinous ligament is nonlinear viscoelastic as in In order 116 to define the boundary conditions, restriction on movements of translation and rotation of the spine has been 117 applied in the lower plane, and defined as having zero displacements. Several charges in the anterior direction 118 were applied as follows: 119 previous studies [10]; a linear elastic model is chosen to represent this behavior.

120
Ansys Workbench software was used for analyzing this geometry and generate the most suitable mesh. For 121 the studied behavior, we used tetrahedral elements, type Solid187 conforming to defined parametric surfaces 122 interfaces \" (Fig. 13) \".

123
It is necessary to mesh the components of the spine with small and confused elements to ensure optimum 124 accuracy of the results of stresses and strains in the inter vertebral discs.

125
The material properties of the spine components were selected after a careful review of the published literature 126 " Table 2"; it was considered appropriate to define the cortical and cancellous bone as homogeneous and isotropic.

127
The magnitudes of 12000 MPa and 100 MPa (cortical and cancellous, respectively) were observed in all studies 128 by various researchers.
129 Table ??: Material Properties Specified in the Model.

130
Since physiologically the nucleus is fluid filled, the elements were assigned low stiffness values (1MPa) and near 131 incompressibility properties (Poisson's ratio of 0.499). Biologically, the annulus fibrosus is comprised of layers of 132 collagen fibers, which attributes to its nonhomogenous characteristics. However, due to limitations in modeling 133 abilities, the annulus was defined as a homogenous structure with a magnitude of 4.2 MPa.

134
This was based on the modulus of the ground substance (4.2 MPa) and the collagen fibers reported in the

148
Finally, the different types of ligaments generated by a tetrahedral mesh to 10 nodes " Table 3". The diagram in 149 \" (Fig. ??) \" shows a person standing of specific global 80kg weight, the overall mass (Head, Neck, Arm (left 150 + right), Forearm (left + right), hand (left + right)) is 13,4517kg to divided by the top surface of the thoracic 151 vertebrae Th1 representing the pressure P1, P2 load represents the mass of the body superior Trunk is 12,768kg, 152 the distance between the point of application of the load and axis (yy ') is 200 mm \" (Fig. 14) \".

153
The total mass of the lower trunk of the human body is equal to 22 kg; represented by P3, the distance between 154 the point of application of the load and the axis (yy ') is 250 mm \" (Fig. 14) \" P4 represents the maximum 155 mass of the backpack is (20 kg), the distance between the point of load application and the axis (yy ') of the 156 spine is (350 mm) \" (Fig. 14) \".

157
For the boundary conditions we fixed the sacrum (Embedding the sacrum) \" (Fig. 14) \". We propose in this 178 Fig (18) shows that the posterior loading presents maximum stresses and strains concentrated in the 179 intervertebral disc D1 that is to say between the sacrum and the lumbar vertebra L5, in the order word the 180 \" (Fig. 19) \" clearly shows that the loading posterior with a lever arm equal 350mm presents maximum Von 181 Mises stresses and strains concentrated in the disc D1 and are respectively equal to (6,9797MPa, 1,7347mm / which are equal to (0,041791mm / mm) relative to the other components of the system of the spine.

192
The posterior load \" (Fig. ??) \" shows clearly that the stresses and strains of Von Mises are concentrated 193 in the two cancellous bone (Th1, Th5) and are respectively equal to (4.6282Mpa, 5.7386MPa) and (0.049594, 194 0.057685) this is mentioned in the (Fig 26) The posterior loading of the backpack with a 350mm lever shown that  (D1) and are equal to (6,9797MPa, 1,7347mm / mm) as noted in the \" (Fig. 18) \", with regard to \" (Fig. 19, 205 20, 21) \" show that the intervertebral disc (D1) is the most damaged which is disc degeneration often occurs 206 after a phase asymptomatic dehydration cracks, tearing of annulus fibrosus (D1 ), the nucleus (N1) can then 207 along these cracks migrate into the ring thickness (D1), and cause acute or chronic back pain, If the core (N1) 208 move around more through the ring (D1), the core can project to the posterior surface of the disc while forming 209 a lumbar disc herniation, this hernia can complete rupture of the ring, migrate laterally into the vertebral canal, 210 or up or down, and even exclude leaving the disk, herniated disc that can come be compressed one or more nerve 211 roots "stuck" near the disc, causing the symptoms of pain "sciatica" when the rear seat of the thigh or "cruralgie" 212 when the seat of pain in the front of the thigh. This justifies that the distance between the load which is the  4,4374MPa, 4,7858MPa, 2,7365MPa) these mentioned in \" (Fig. 18) \", on the other hand \" (Fig. 19) \"clearly 220 shows the elastic strain is higher in the four intervertebral discs (D1, D15, D16, D17) that are equal (1.7347, 221 1.0586, 1.1463, 0 66065), which justifies that the distance between the load which is the point of application of 222 the load and the axis of the spine plays a very important role in increasing the solitation of the latter.   Figure 26: Table 3 : .