An examination of the mechanical properties of the annulus fibrosus: The effect of vibration on the intra-lamellar matrix strength

Vibration has been associated with low back pain and disc herniation; however the mechanism responsible for this association is unclear. It is theorized that herniation propagates through annular layers via clefts that form in the extracellular matrix between collagen fibres (intra-lamellar matrix) within each lamella. The effect of cyclic compressive loading at 5 Hz, applied to porcine functional spine units, on the mechanical properties of excised single annular lamellae was examined. These lamellae were tested under tension applied perpendicular to the collagen fibre orientation, effectively isolating the intra-lamellar matrix. Vibration affected the deformation magnitude at the end of the toe region of the stress–stretch ratio curve; specifically vibrated tissues showed larger toe regions (stretch ratio of 1.50 as compared to 1.31 observed in the control tissues, p = 0.027). It is hypothesized that this result may be due to damaged elastin—a protein responsible for minimizing deformation and assisting with returning tissues to normal length following tension.