Table 1. Vertebrae and intervertebral disc (IVD) material mapping (density-intensity-modulus) relations used in the current finite element analysis (FEA).
| Property | Mapping relations |
|---|---|
| Apparent density (ρapp in kg/m3) | ρapp =47 + 1.122 * HU |
| Ash density (ρash in kg/m3) | ρash =0.6 * ρapp |
| Elastic modulus (E in MPa) | Ez =−349 + 5.82 * ρapp |
| Ex = Ey =0.333 Ez | |
| Z: axial direction of the vertebra | |
| Shear modulus (G in MPa) | Gxy =0.121 Ez |
| Gxz = Gyz =0.157 Ez | |
| Poisson ratio (V) | Vxy =0.381 |
| Vxz = Vyz =0.104 | |
| Maximum principal stress limit (σ in MPa) | σ =137 * ρash1.88, ρash <0.317 |
| σ =114 * ρash1.72, ρash >0.317 | |
| Plastic strain (εAB) | εAB =−0.00315 + 0.0728ρash |
| Minimum principal stress limit (σmin in MPa) | σmin =65.1 * ρash1.93 |
| Intervertebral disc − annulus fibrosus, elastic modulus (MPa), Poisson’s ratio | 500, 0.3 |
| Intervertebral disc − nucleus pulposus, elastic modulus (MPa), Poisson’s ratio | 8, 0.499 |
This table shows material mapping relations and transversely isotropic material properties used for the vertebrae. The plastic strain and strength data of the vertebrae is also given. Finally, the IVD elastic constants are given. HU, Hounsfield unit.