THE RESPONSE OF THE HIERARCHICAL STRUCTURE OF THE INTERVERTEBRAL-DISK TO UNIAXIAL COMPRESSION

The time-dependent mechanical response of the canine intervertebral disc in axial compression is related to the response of the various levels of the hierarchical organization. In stress relaxation the initial transverse bulging of the disc recovers almost completely with time. The corresponding decrease in volume correlates with the measured loss of water from the disc. The three-dimensional architecture of the disc, examined by sectioning isolated discs that had been fixed in compression, accommodates the volume displacement. Bulging of the peripheral lamellae is minimized by the curvature of the vertebral interface and by stress-driven transport of water out of the disc through the cartilage end-plates into the vertebral bodies. Even though the disc undergoes macroscopic compression, the fibres of the lamellae are loaded in tension and their mode of deformation is compared with that of other connective tissues such as tendon and intestine.