|Each cervical disc begins as a "pancake" which is a little
thicker at the center than at the sides, front or back. It has a
rounded front and rounded sides to match the contours of the
vertebral column and it is a bit concave on the back surface to
accommodate the spinal canal. This results in a "kidney bean"
shape. There is an outer ring of rather tough, gristly cartilage
(the annulus) and an inner core of different, softer cartilage
(the nucleus). Degeneration of the disc can be seen as a change
in the signal on an MRI scan as the physical consistency of the
nucleus material becomes even softer. With this softening, the
material becomes more fluid and deformable. Due to weight and
forces on the spine during movements which squeeze the disc
between the vertebral bodies, the nucleus tries to bulge
outward. Sometimes the annulus is thinned out or pushed ahead of
the deforming nucleus material. Sometimes a piece of the nucleus
works its way through a crack in the annulus. This is called a
disc herniation. I li