Biomechanical analysis of damaged intervertebral disc using reflective photoelasticity

This paper presents an experimental evaluation of the structural integrity of the lumbar section (L2-L3-L4) considering a damaged intervertebral disc. In this study, porcine specimens were used due to the similarity of the mechanical properties of those of the human spine. The lumbar section L2-L3-L4 was tested under compression. Five cases were analyzed; in the first one, the lumbar section consisted of healthy intervertebral discs. For the other four cases, the disc located between L2 and L3 was divided into four quadrants: front, back, left and right. For each of these cases, a damage condition was induced by making an incision from the annular fibers to the pulpous nucleus, covering each quadrant; the back elements (pedicles and facet joint) were removed and only the vertebral bodies and discs were tested. As a damaged intervertebral disc is unable to properly perform its mechanical function, the load transferred from L2 to L3 through the disc is no longer optimal. The actual stress field on L3, considering the damaged disc, was obtained using reflective photoelasticity for each one of the previously mentioned study cases. The results show that the induced damage in the intervertebral discs increases the stresses on L3 considerably when compared to the case of an undamaged disc, being the most critical when the damage is located in the back quadrant of the disc. In the other three cases, the damaged disc does not reduce the structural integrity of the vertebral body significantly. However, the inter-vertebrae space is reduced as a result of the damage, thus compromising the structural integrity of the studied lumbar section.