The in situ microenvironment of the intervertebral disc is inhomogeneous and structurally complex. Applied whole body loads result in complex patterns of load distribution that expose cells to a strain environment that cannot be directly inferred from applied load. Cells in the intervertebral disc, as in other connective tissues including tendon, ligament and bone form interconnected cellular networks that are linked via functional gap junctions allowing the cells to span the tissue and to interact with each other as well as with the surrounding extracellular matrix. Cell networks are necessary to effect a coordinated response to mechanical and environmental stimuli. This response is required both for healthy tissue maintenance, and also in response to tissue injury and degeneration (Wilson, Close et al. 2000;​ Cowin 2002).

Using confocal microscopy, the in situ strain environment of the outer annulus of an intact disc and the effect of high level flexion on gap junction signalling were explored. A transient disruption in gap junction signalling interruption was shown under high flexion load. The in situ strain environment in the collagen matrix of the outer annulus under high level flexion was quantified in regions close to cells for three magnitudes of flexion and revealed highly compressive fibril-oriented intercellular strains. Fibril-oriented surface strains were significantly higher than in situ strains, which implies a mechanism of load redistribution that acts to minimize strain along the fibrils. Fibril sliding occurred under low load, but did not increase with higher flexion, suggesting that fibril sliding is important in the initial stages of load redistribution. This dissertation provides the first examination of the in situ strain environment in the outer annulus fibrosus of an intact intervertebral disc under high flexion load.