The influence of strain rate on the compressive stiffness properties of human lumbar intervertebral discs.

The purpose of this study was to develop the compressive stiffness properties of individual lumbar intervertebral discs when subjected to various dynamic compressive loading rates. A total of 33 axial compression tests were performed on 11 individual human lumbar functional spinal units dissected from 6 fresh frozen human cadavers, 5 male and 1 female. The proximal and distal vertebral bodies were fixed to load cells with a custom aluminum pot, and subjected to a dynamic compressive loading at three different strain rates; 6.8, 13.5, and 72.7 strain/ sec. The results show that the compressive stiffness of lumbar intervertebral discs is dependent on the loading rate. There was no significant correlation (p > 0.05) between FSU compressive stiffness and vertebral level at any of the three loading rates. Therefore, a linear relationship between loading rate and vertebral disc compressive stiffness was developed by curve fitting the stiffness data from the current study along with the stiffness data reported by previous studies.