A biomechanical study of L5-S1 low-grade isthmic spondylolisthesis using a personalized finite element model.

The pars interarticularis lesions in isthmic spondylolisthesis result generally from mechanical stresses in the neural arch due to repetitive overload during daily activities or to trunk imbalance resulting from spino-pelvic morphology. The L5-pelvis junction of a low-grade isthmic spondylolisthesis patient was modeled using a personalized finite element model to investigate the biomechanical behavior of the L5-S1 motion segment. Stress distribution and facet contact pressure in the altered segment were analyzed under 500 N simulating the gravitational load. High von Mises stresses were located in the pars interarticularis, in the pedicle, and in the outer region of the annulus. A high contact pressure was obtained at the facet surfaces. Influenced by the pelvic morphology, the inclination of L5-S1 junction affects the resulting shear forces and may play a crucial role in spondylolisthesis development.