THE RELATIONSHIP BETWEEN LOAD TRANSMISSION AND DISC DEGENERATION IN THE THORACOLUMBAR SPINE: A FINITE ELEMENT STUDY

Abstract

Degenerative changes to the intervertebral disc structure appear gradually in the aging process, and are likely to affect the fracture patterns of the thoracolumbar vertebral body — a common site of spinal injuries — by changing the mechanical interaction within each motion segment. This study focused on the influence of disc degeneration on the mechanism of load transmission through the thoracolumbar vertebral body. Compressive stresses and ways of load transmission were examined in cases of normal and degenerated discs. The stress analysis was performed using the finite element (FE) method. For normal discs, the highest compressive stresses were found in the central region of the discs, corresponding to the anatomical nucleus. Such high stress made the endplates bulge towards the vertebral bodies. Hence, the fracture would most probably start in the center of the endplate. For degenerated discs, the peak stresses rose to high levels in the annuli. Thus, the annulus was mostly under compression, and so was the periphery of the endplate, with much less deflection at its center. The failure of the vertebra was due to the fracture of the periphery of the endplate. Ways of load transmission through the vertebral body were strongly affected by the disc condition.