Collagen fibre orientation in the annulus fibrosus of intervertebral disc during bending and torsion measured by x-ray diffraction.

X-ray diffraction has been used to measure the orientation of the collagen fibres in the ventral annulus fibrosus of intact L 1/2 rabbit intervertebral discs during in vitro bending and torsion. Fibres are tilted with respect to the axis of the spine. As predicted by theory, fibre tilt decreases in those regions of the annulus which are stretched by bending but increases in the slackened regions. Good agreements with the quantitative predictions of bending theory was obtained in three of the six series of experiments, the predicted trend being found in all six. Tilt direction alternates in successive lamellae of the annulus. When discs were subjected to both clockwise and counterclockwise torsion of 5 degrees, the two families of tilted fibres reoriented in the expected directions.