Biomechanical study of spinal cord and nerve root in idiopathic scoliosis: based on finite element analysis

Abstract Background Limited research on spinal cord and nerve root biomechanics during scoliosis correction, this study assesses surgical impact using finite element analysis. Methods A detailed three-dimensional finite element model was constructed, incorporating vertebral bodies, ligaments, spinal cord, and nerve roots using engineering software. The Cobb angle was incrementally corrected by applying forces and displacements. At a 40mm displacement, mean von Mises stress on the spinal cord and bilateral nerve roots in each spinal segment was compared between traction versus traction + torsion, and pushing versus pushing + torsion conditions. Parametric t-tests were used for spinal cord stress comparisons, while non-parametric Mann-Whitney U tests were employed for nerve root stress comparisons. T1/2-T4/5 was defined as the upper segment, T5/6-T8/9 as the middle segment, and T9/10-L1/2 as the lower segment. The average von Mises stresses of the upper, middle and lower segments of spinal cord and nerve root were compared under different displacement conditions by non-parametric Mann-Whitney U test, α = 0.05. P < 0.05 was considered statistically significant. Results Increasing displacement reduced the Cobb Angle, increased correction rates, and elevated stress on the spinal cord and nerve roots. At 40 mm displacement, stress on the right nerve root in the apical vertebra region exceeded that on the left nerve root in the thoracic curve, with peak stress observed near the apical vertebra on the spinal cord. Notable stress differences were observed between traction and traction + torsion conditions but not between pushing and pushing + torsion conditions. Compared with the displacement of 20 mm and 40 mm, significant stress differences were noted in the middle spinal cord segment under all conditions and in all spinal cord segments and nerve roots under pushing conditions. Conclusions Achieving correction rates between 61–68% primarily affected the apical vertebra region of the spinal cord. In the case of similar correction rate, the traction maneuver has the least stress on the spinal cord and bilateral nerves, and the push maneuver can achieve a greater correction rate. However, with the increase of correction rate, the push maneuver will significantly increase the risk of nerve injury.