The influence of the nucleus pulposus on the stress distribution in the natural and prosthetic intervertebral disc

The aim of this article was to present the results of a preliminary study on the stress distribution in the lumbar intervertebral disc [IVD] under loads induced during daily activities. Basic anatomy, biomechanical analysis of the vertebra and intervertebral disc were introduced. The third and fourth lumbar vertebrae were chosen for the study because they carry considerably higher loads, especially while standing or sitting. The static mechanical analyses using the finite element method (FEM) were conducted for four standard loads reflecting patient's positions: recumbent, standing, sitting and standing with additional loads, and three models: an intervertebral disc with an inner nucleus pulposus and two prosthetic intervertebral discs, with or without an artificial nucleus. The FEM analysis was performed in the SolidWorks Simulation module on reverse-engineered 3D models of vertebrae and the intervertebral disc, based on a series of computed tomography [CT] scans of the patient's spine, which had been properly processed in Materialise Mimics software and exported to CAD files. The model of the fourth intervertebral disc, placed between third and fourth vertebra, had been additionally modified to include its inner core, the nucleus pulposus.