Effect of lumbar anterior longitudinal ligament rupture on initial instrument fixation

a three-dimensional finite element method study

Abstract

Recent studies on adult spinal deformity report complications including anterior longitudinal ligament (ALL) rupture, which may cause instrumentation failure. This study aimed to evaluate the effect of ALL rupture on instrumentation failure. We used a three-dimensional finite element method (3D-FEM) to study the rupture of the ALL. A 3D-FEM model of the lumbar spine was generated using computed tomography images. A posterior instrument was then adapted to the L1-S1 vertebrae as a fixed model. Simulations of ALL rupture were performed at L3/4 in 25% increments and virtual excision of the intervertebral disc (IVD) was performed for each model. Thus, we prepared standard models and L1-S1 fixed models with and without disc excision under ALL rupture conditions. We evaluated displacement (mm) during extension and the von Mises stress (MPa) on the IVD, vertebral body around the screws, and posterior instrument. In the standard models, with and without disc excision, displacement during extension and the stress on IVDs increased as the degree of ALL rupture increased. In L1-S1 fixed models, the displacement similarly increased. The stress on IVDs, vertebral bodies around the screws, and posterior instruments also increased. ALL rupture may pose a potential risk of vertebral instability, leading to instrumentation failure.