Numerical Simulation of Degeneration of Lumbar Spine Segments

Abstract

Numerical analyses are able to simulate processes in their progress that are impossible to measure experimentally, like aging and spinal degeneration processes. 3D FE simulations of aging and sudden degeneration processes of human lumbar spinal segments are presented for compression. The goal of the study was to determine the separated and combined effect of the main mechanical degeneration parameters on the deformation and stress state of the lumbar functional spinal units (FSU) during long- and short-term degeneration processes.

Degenerations were modeled by changing the geometry and material properties of segments. Five grades of degeneration were distinguished from healthy to fully damaged cases. Sudden degenerations were modeled by considering the actual grade of aging degeneration state at which it starts to occur. Systematic numerical analyses of degeneration processes were investigated by considering the separated and mutual effects of the main mechanical causing phenomena.

During the aging process, first the effect of loss of incompressibility of nucleus, later its increasing hardness dominated, yielding the smallest compressive stiffness of the whole disc at mildly degenerated state. In sudden degeneration processes the smallest stiffness belonged also to the mildly degenerated state. Vertical intradiscal stresses showed significant change during aging. Disc deformability and bulging was maximum in mildly degenerated state and decreased during aging.

The most important factor in segmental stability is the change of nucleus stiffness. For both long-term aging and sudden traumatic degenerations, the smallest compressive stiffness of disc and the highest risk of segmental instability happen at mildly degenerated state. The disc deformability and bulging is maximal in mildly degenerated state, and increases suddenly in accidental degeneration that may lead to injury in young age again. These effects explain that the segments are most vulnerable in young age; consequently, low back pain problems insult so frequently the young adults.