Intradiscal pressure in the degenerated porcine intervertebral disc.

Measuring intradiscal pressure is one way of mechanically assessing the discs degenerative state. In this study, the load-bearing capacity of degenerated and their adjacent lumbar intervertebral discs was evaluated using two different injury models. Seventeen adolescent pigs were divided into two groups, an annulus injury group and an endplate injury group. The annulus injury group was subjected to a stab incision in the L3-L4 disc, whereas the endplate injury group received a cranial endplate perforation of the L4 vertebral body. Both groups were biomechanically evaluated three months later using a miniaturized servohydraulic testing machine across L2-L4 and with two pressure needles inserted into the nucleus pulposus of the L2-L3 and L3-L4 discs. Linear relationships between the intradiscal pressure and the applied load were determined within the load range studied. When comparing the ratio of the injured to the adjacent disc pressure, the endplate injury was lower (mean value 0.31) than the annulus injury (mean value 0.51). The pressures in the discs adjacent to the degenerated level were found to be slightly higher. This increase can be expected due to a redistribution in mobility demands in segments adjacent to those with increased stiffness, i.e. degenerated intervertebral discs.