The effect of intervertebral disc simulated damage on the human spine biomechanics.

More than 50% of intervertebral discs in the third and fourth decade of life exhibit annular tears and fissures with different orientations and extents. On the other hand, in vitro biomechanical investigations of the disc surgery treatment, sometimes requires collaterals lesions, such as incision or disc material removal to recreate biological injuries, as in discoplastly. These lesions could have a mechanical impact on the spine flexibility and in the surrounding tissue and could alter the final outcomes of in vitro studies. The influence of the presence of lesions on the biomechanics of the segment is still a debated research question. Thus, this in vitro study aims to evaluate changes in spine biomechanics, in terms of stiffness, range of motion and disc height, induced by an increasing damage of human disc. In order to assess the impact of the annulus damage on the surrounding tissues, principal strain distributions were investigated in the lateral side opposite than the damaged region. Eight fresh cadaver thoraco-lumbar FSUs were used in this study. The specimens were tested sequentially in flexion and extension in five different configurations: a) with the intact disc; b) with two vertical cuts; c) with four cuts, forming a square, without removing any part of the annulus; d) after having removed the cut part of the AF; e) after having removed the nucleus pulposus. Image analysis and surface strain distribution were performed on the lateral disc by means of the Digital Image Correlation.