A patient specific computational biomechanical model for the entire lumbosacral spinal unit with imposed spondylolysis. (August 2019) - Haj-Ali, Rami
Abstract: Background: A biomechanical model of the lumbosacral spinal unit between L1-S1 was developed to investigate the behavior of normal and select pathological states. Our aims were to generate predictive structural models for mechanical deformation including critical stresses in the spine components and to investigate the probability of subsequent lumbar spine fractures in the presence of unilateral spondylolysis. Methods: A non-linear three-dimensional finite element pathology-free model of the L1-S1 lumbosacral unit was generated using patient-specific computerized tomography scans and calibrated by comparing it to experimental data of a range of motion modes consisting of flexion, extension, left and right lateral bending, and left and right axial rotation. Unilateral and bilateral pars defects were created on the isthmus of L5 to simulate spondylolysis. Findings: Results showed that under flexion, left lateral bending and right axial rotation, stresses were higher on the contralateral L5 pars-interarticularis, whereas, no significant changes occurred on the left-right isthmus of the L2-L4 and S1. Significant changes in the range of motion compared to the pathology-free model were observed in bilateral spondylolysis not only adjacent to the pars defect area but also in other lumbar spine levels. Interpretation: The proposed pathology-free lumbosacral unit model showed good correlation with experimental tests for all loading cases. In unilateral spondylolysis, a subsequent pars defect was observed within the same vertebra. The overall modeling approach can be used to study different pathological states. Highlights: A 3-dimensional non-linear lumbar spine finite element model has been developed. The model with unilateral spondylolysis showed no changes in range of motion above L5-S1. The model with bilateral spondylolysis showed significant differences in the range of motion above L5-S1. In unilateral spondylolysis, the L5 right isthmus had greater stresses in all spinal motions. The bilateral pars defects caused higher stress concentrations in the intervertebral disc