[Introduction to the biomechanics of the lumbar spine].

The first part of this report is devoted to the functional anatomy of the lumbar spine, and reminds of the morphology, structure and proper physiology of each lumbar vertebral component, and then of each flexible element linking the lumbar vertebrae with one another. In this tripod system, the column of vertebral bodies and discs play an essential role, while the two columns of posterior articular processes have a supplementary, but nevertheless effective role in spinal stability and mobility. The intervertebral disc, because of the strong osmotic pressure of the nucleus and the dual direction fibrillar structure of the annulus, is in a pre-stress condition and constitutes a very strong visco-elastic shock-absorber; besides, it is a flexible structure allowing free motion. Under certain circumstances, it is supported by the abdominal wall. The second part of this report shows how spinal mobility in all directions, and absorbing of the load in all body postures, are effected by the lumbar spine.