A semi-experimental stress analysis of the human intervertebral disk in compression

Abstract

The intervertebral disk is a heavily loaded component of the human body. In the lumbar region, in vivo measurements by Nachemson (1966, 1970)4–5 show compressive loads in the range of 1000–3000 Newton under normal living conditions. Determination of stresses in intervertebral disks is, thus, a relevant biomechanical problem that has been studied experimentally and from a clinical point of view by Nachemson (1960, 1963, 1966, 1970).2–5 Galante (1967)1 investigated tensile properties of the lumbar annulus fibrosus. Nachemson found the state of stress in the nucleus pulposus to be hydrostatic, and Galante's investigation revealed a considerable inhomogeneity of the material in the annulus fibrosus. In this paper, the effect of material inhomogeneity on the distribution of stress in annulus fibrosus is studied. On the basis of previous experimental findings and complementary measurements of the lateral pressure distribution through the disk, the tangenital and radial stress distributions are determined theoretically. The results of the theoretical analysis show that inhomogeneity influences the distribution of tangential stress considerably, whereas only heavy lateral pressure gradients disturb this same stress distribution to any significant extent. Experimental results show that high pressure gradients may well be present in annulus. Only pure compression of the disk is considered.