Dynamic stiffness and damping of human intervertebral disc using axial oscillatory displacement under a free mass system.

The aim of this study was to analyse the dynamic response of the human intervertebral disc to vibration in a physiologically relevant frequency spectrum. Eight lumbar intervertebral discs were harvested. After preparation, each sample was subjected to a pre-loading and then dynamic compression (from 5 to 30 Hz). The dynamic compression was applied using an experimental set-up comprising a free weight loading from above and a driving oscillatory displacement from below (closest to the in vivo loading). A viscoelastic model enabled the calculation of stiffness and damping from the transfer function. From 5 Hz to 30 Hz the stiffness values are between 0.19 and 3.66 (MN/m) and the damping values between 32 and 2094 (Ns/m). The mean resonant frequency was found at 8.7 Hz. These dynamic characteristics of the intervertebral disc could be used in a three-dimensional finite elements model of the human body to study its response to vibration in the driving position.