Study on noninvasive estimate method for intervertebral disk load at lumbar vertebrae

Abstract

Lumbago occurs when load causes malformation of the flexible intervertebral disks of the lumbar vertebrae. The conventional method of measuring load on the intervertebral disk is an invasive method in which the internal pressure of the intervertebral disk is measured by directly inserting an electrode. In this study, intervertebral disk load is derived indirectly by the noninvasive estimation method that uses three-dimensional motion analysis system and signal processing to estimate the shape of the lumbar vertebrae. Specific estimation method is shown as follows. First, vertebra is assumed to a rigid body. Next, lumbar vertebrae are approximated with an arc using 3-D positional coordinates. Finally, average of the intervertebral gap is estimated. Accordingly, because the proposed method only entails applying markers to the surface of the back and taking pictures with cameras, it is safe and does not require surgical procedures. Furthermore, this method allows estimation of intervertebral disk load in a moving subject. In this paper, the proposed method is described in detail. And an experiment in which intervertebral disk load is estimated from stationary postures is executed. Moreover the proposed method is compared with the conventional method. As a results, the experiment shows that the proposed method is effective in that the magnitude correlation tendencies of intervertebral disk load estimated with the proposed method are qualitatively consistent with the tendencies calculated from actual measurements of internal pressure. ©2012 The Japan Society of Mechanical Engineers.