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The
soft nucleosus may extrude through the annulus tear. This is referred
to as a prolapsed disc or a ‘slipped disc’. The prolapsed
disc may cause compression or inflammation of an adjacent nerve root,
resulting in sciatica. Prolapsed discs are usually diagnosed on an
MRI scan. |
(Fig.
4 A discogram showing leakage of contrast material from a disc annulus
tear) |
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Disc
degeneration may also result from inadequate disc nutrition. When
the blood supply from the adjacent vertebrae is impaired, disc degeneration
may be accelerated. Cigarette smoke is a significant risk factor for
accelerated disc degeneration. The soft, pulpy nucleus may become
dehydrated and its collagenous fibres undergo degradation. The degenerate discs may be a source of chronic back pain. |
(Fig.
5 An end-stage dehydrated disc showing loss of disc height and ligament
thickening) |
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The
dehydrated discs can be seen on an MRI scan. They are also known as
‘black discs’ because of the colour change on MRI. It
is important to know that not all black discs are painful. Confirming
that a particular degenerate disc is the source of back pain may be
very difficult. Other tests, such as discography may be helpful in
diagnosing the cause of back pain. |
(Fig.
3 A ‘black disc’ associated with a torn annulus) |
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Ultimately,
the disc may lose its shock absorbing ability. The disc space will
become narrow and movement at that level will be abnormal. This places
excessive strain on the adjacent weight-bearing structures in the
spine, such as the facet joints. Excessive strain on the facet joints
and surrounding ligaments may cause them to hypertrophy (enlarge).
Joint hypertrophy and ligament thickening reduces the space available
for the adjacent nerve roots. This may cause nerve root compression,
a painful condition called spinal stenosis. |
(Fig. 6 An x-ray showing a chronic degenerate
disc) |
© Copyright of the South African Spine Society |