An accurate validation of a computational model of a human lumbosacral segment

Clinical studies have recently documented that there is sufficient evidence to suggest that abnormal motion may be an indicator of abnormal mechanics of the spine and, therefore, may be associated with some types of low-back pain. However, designating a motion as abnormal requires knowledge of normal motions. This work hence aims to develop an accurate computational model to simulate the bio-mechanical response of the whole lumbosacral spinal unit (L1-S1) under physiological loadings and constraint conditions. In order to meet this objective, computed tomography (CT) scanning protocols, finite element (FE) analysis and accurate constitutive modelling have been integrated. Then the ranges of motion (ROM) under flexion, extension and lateral bending moment were measured and compared with experimental data, finding an excellent agreement. In particular, the ability of the model to reproduce the relative rotation between each couple of vertebrae was proved. Finally, the shear stresses for the most extreme load cases were reported in order to predict which are the most risky conditions and where the maximum damage would be located. The results indicate that the greater values of the stresses were located at L4-S1 levels just in the interfaces between disc and vertebrae across the posterior and posterolateral zone. This result can be clinically correlated with the existence of damage exactly where the stresses were maximal in the proposed finite element model.