X-ray diffraction demonstrates reorientation of collagen fibres in the annulus fibrosus during compression of the intervertebral disc.

The annulus fibrosus of the intervertebral disc is reinforced by tilted collagen fibres. It has been predicted that the tilt angle should increase as the disc was compressed. This prediction has now been confirmed using X-ray diffraction. Diffraction patterns were recorded from the ventral annulus of intact L1/2 rabbit discs during various stages of compression. At each stage the ventral height was measured. Fibre tilts were measured from the diffraction patterns and found to increase as the disc was compressed. For five out of six discs the quantitative dependence of tilt on compressed height was in good agreement with theoretical predictions; the sixth did not compress evenly but an increase in tilt was still observed.