The relationship of degeneration of the intervertebral disc to mechanical loading conditions on lumbar vertebrae.

Degeneration of lumbar intervertebral discs is typical for the aging process and contributes to common low-back problems. It is likely to influence vertebrae by changing the mechanical interaction within each motion segment. This study focuses on the influence of disc degeneration on the mechanism of load transmission through the lumbar vertebral body. Effective stresses, ways of load transmission and failure modes of vertebral body were examined in cases of healthy and degenerated discs. The stress analysis was performed using the Finite Element Method. For healthy discs, the highest effective stresses were found in the center of bony end-plates. For degenerated discs, they were found in the lateral aspects of the end-plates, in the cortical wall, and also in the vertebral body rims. However, regardless of the disc condition, the highest effective stresses do not occupy the whole thickness of the endplate and/or the cortical wall, but are concentrated near the spongy core. Ways of load transmission through the lumbar vertebral body and modes of eventual damage to it are also strongly influenced by the disc condition.