05 - Analysis of Compressive Distributional Load of Intervertebral Disc L4-l5 by Meand of Photoelasticity

INTRODUCTION In last decade, it has been seen an aging process of world population, due to an increase of life expectancy (SZPALSKI et al., 2003). The aging process is related to a higher rate of spine diseases, such as low back pain. In spite of the high numbers of factors related to development of low back pain and discal hernias. The discal hernias have been pointed as one of the main structures involved to etiology of low back pain (KUSLICH, ULSTROM and MICHAEL,1991). These diseases affect mainly the intervertebral disc L4 and L5, due to highest load (ADAMS et al., 1993; ADAMS et al., 2000; KUSLICH, ULSTROM e MICHAEL, 1991; RANNOU et al., 2001). The discal cells are sensitive to mechanical involvements, being directly influenced by hydrostatical pressure and compressive load (GUEHRING et al., 2006; HANDA et al., 1997; ISHIHARA et al., 1996). These cells are able to distribute and minimize compressive load between adjacent vertebrae due to viscoelastic properties (ADAMS e DOLAN, 1995; AWAD e MOSKOVISH, 2006; FERGUSON e STEFFEN, 2003). Loads are transmitted through vertebrae plate, by central area, the pulpous nucleus (McNALLY e ADAMS, 1992; McNALLY, NAISH e HALLIWELL, 2000). Photoelastic is a science that studies physical effects by light due to action of tensions or deformations in transparent elastic bodies (DALLY e RILLEY, 1978; DOYLE e PHILLIPS, 1978) and, it has been one of the techniques available for determining and evaluating the distribution of internal stress in structural systems (MAHLER e PEYTON, 1955). It is an experimental technique that allows a qualitative and quantitative analysis of state of internal stress of materials by means of view of optical effects (HIROKAWA, YAMAMOTO e KAWADA, 1998; RUBO e SOUZA, 2001).