Cracks in the posterior
annulus.
It
is an important part of my argument that material from the nucleus reaches and
affects nerves in the posterior annulus.
Whether this occurs through cracks or by seepage through the walls of
the annulus I don't know. If it is
mainly by cracks then the formation of these cracks in the annulus is an
important part of the mechanism of the "shape warning pain".
However
strong the disk is, it cannot protect itself from the effects of
hyperflexion. The danger of a prolapsed
disk on hyperflexion is inherent in the overall mechanical arrangement of that
part of the human spine and pelvis. It
may seem illogical to suggest that evolution might select for a disk which is
more liable to cracking but if that deficiency actually is important to the
shape warning pain then that deficiency in the disk will actually protect the
disk.
Thus
on this logic the evolution of the lowest discs of the human spine together
with the evolution of the shape of the spine and pelvis might have evolved
discs which are more liable to degeneration.
I'm
not suggesting that this is necessarily the case but it needs to be thought
about.