[Mechanical influences on the lumbar spine]

The author investigated the firmness and elasticity of the lower lumbar vertebrae and intervertebral discs. They confirmed that the intervertebral disc is very firm when exposed to pressure and very coherent when exposed to traction. The locus minoris resistentiae during traction tests and when testing resistance to impacts is the connection between the intervertebral disc and the body of the vertebra. The bodies of vertebrae are less resistant to pressure than lumbar intervertebral discs. When exposed to an impact, imitating bending, the intervertebral disc is torn from the body of the vertebra. The most vulnerable place of the lumbar spine is thus the connection of the vertebra and the intervertebral disc, the site which is also the borderline of the vascular supply which then changes into diffuse supply. Strain at the borderline of firmness or above it can cause degeneration of the intervertebral disc, and if more extensive, even spondylolisthesis.