Biomechanical properties of human intervertebral discs subjected to axial dynamic compression. A comparison of lumbar and thoracic discs.

This investigation revealed biomechanical properties and some morphological parameters of isolated intervertebral discs at various disc levels. One hundred twenty-three specimens were subjected to axial dynamic compressive loads. The duration of testing was 5 minutes, the loads Fd1 = 650 N +/- 400 N (discs from T5-6 to L1-2) and Fd2 = 950 N +/- 540 N (discs from T9-10 to L5-S1). Down the spine, the mean disc heights and cross-sectional areas increased; the water content seemed to be nearly constant. Axial deformation and ventral bulging increased down the spine as well, which is mainly due to the increasing disc height. Creep showed different characteristics. It was smallest within the region T10-11 to L1-2 and increased above and below this level. The increase below L1-2 is mainly due to the increasing disc height; the increase above T10-11 occurs because the thoracic discs behave in a more viscous manner than the lumbar discs.