IVD ARCHITECTURE – NEW APPROACHES REVEAL NEW STRUCTURAL COMPLEXITIES, AND THEIR FUNCTIONAL IMPLICATIONS

Abstract

Most researchers have employed conventional histological and related methods to investigate the complex architecture of the IVD. Recognizing the inherent limitations of these methods we have pioneered new microstructural and micromechanical techniques that have greatly enhanced our understanding of the 3-D architecture of the IVD. Using sectioning planes that take full account of the oblique fibre angles in the annular wall, combined with specialized optical imaging techniques that provide high resolution structural images of fully hydrated thick sections we have described new levels of structural complexity that are clearly implicated in the biomechanical function of this highly complex connective tissue organ.

The primary regions of structural interest are the annulus, the annular-endplate junction and the nucleus-end-plate junction. Within the complex multilayered annular wall we have identified a system of collagen-rich bridging structures that both integrate proximate oblique and counter-oblique layers as well as providing long-range radial continuity across many layers. We argue that this system has an important biomechanical role of lashing alternate ‘like’ layers together whilst providing for some freedom of fibre angle change between immediately adjacent layers coursing in counter oblique directions. Thus, under the deformations generated by direct compressive, bulging, flexion and minor rotational forces, the structural integrity of the annulus is maintained.

We have also clarified important features of both annular/endplate and nucleus/endplate structural integration. Our very recent structural studies of the lumbar motion segment suggest that the current models of disc/endplate integration require substantial revision. This presentation will describe new experimental evidence in support of a more appropriate model of structural integration.