Biomechanical evaluation of the thoracolumbar spine comparing healthy and irregular thoracic and lumbar curvatures

The geometric alignment of the spine plays an integral role in stability, biomechanical loading, and consequently, pain, and a range of healthy sagittal curvatures has been identified. Spinal biomechanics when sagittal curvature is outside the optimal range remains a debate and may provide insight into the load distribution throughout the spinal column.

A thoracolumbar spine model (Healthy) was developed. Thoracic and lumbar curvatures were adjusted by 50% to create models with varying sagittal profiles: hypolordotic (HypoL), hyperlordotic (HyperL), hypokyphotic (HypoK), and hyperkyphotic (HyperK). In addition, lumbar spine models were constructed for the former three profiles. The models were subjected to loading conditions simulating flexion and extension. Following validation, intervertebral disc stresses, vertebral body stresses, disc heights, and intersegmental rotations were compared across all models.

Overall trends demonstrated that HyperL and HyperK models had a noticeable reduction in disc height and greater vertebral body stresses compared to the Healthy model. In comparison, the HypoL and HypoK models displayed opposite trends. Considering the lumbar models, the HypoL model had reduced disc stresses and flexibility, while the contrary was observed in the HyperL model. Results indicate that the models with excessive curvature may be subjected to greater stress magnitudes, while the straighter spine models may reduce these stresses.

Finite element modeling of spine biomechanics demonstrated that variations in sagittal profiles influence the load distribution and range of motion of the spine. Considering patient-specific sagittal profiles in finite element modeling may provide valuable insight for biomechanical analyses and targeted treatments.