nucleus pulposus
annulus fibrosus
disc prolapse
A
B
disc extrusion
disc sequestration
C
D
Figure 4.1 The four stages of disc damage, leading to herniation (pro-
lapse) of disc material.
A: Annular tear. At this stage the disc is intact and there is only a small tear
in the tough outer layer (annulus fibrosus).
B: Disc prolapse. The soft centre of the disc (nucleus pulposus) is now start-
ing to protrude from its normal position, but is still contained within the outer
layer.
C: Disc extrusion. At this point the soft nucleus has broken through the annu-
lus fibrosus.
D: Disc sequestration. At this point the nucleus has broken through the annu-
lus fibrosus and a piece of the nucleus has broken off from the rest and is lying
loose in the spinal canal.
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