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Family
Doctor Books |
Preview of Understanding Back Pain
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How the spine works |
The spine or backbone is known medically
as the vertebral column. Its role is to support the whole body, be capable
of bending and twisting in all directions, and at the same time protect
the vital structures such as nerves that run through it. What’s
more, it has to last a lifetime. No engineering structure comes anywhere
near meeting such specifications, so it is hardly surprising that problems
can arise from time to time.
The vertebral column
Vertebrae
The human spine consists of a column of bony blocks
known as vertebrae, which sit one on top of another, joined together
by tough ligaments to form the vertebral column. There are seven cervical
vertebrae in the neck, twelve dorsal or thoracic vertebrae in the upper
and middle back, and five lumbar vertebrae in the lower part of the spine.
The fifth lumbar vertebra is known as L5 and sits on the sacrum, which
in turn is connected to the coccyx – the tail bone. The sacrum consists
of several vertebrae that have joined together. The sacrum is joined
at its edges to the pelvis – the ring of bone that carries the trunk
and which in turn is supported by the hips.
The spine
or backbone is a truly amazing engineering structure, allowing
a huge range of movement while supporting the body and the vital
structures, such as nerves, that run within it.
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- Discs: The spine is not a rigid structure.
It is able to bend and twist because there are flexible cushions
or discs between each of the vertebrae. Each disc is a flat, biscuit-shaped
structure with a jelly-like centre called the nucleus and an extremely
strong outer skin called the annulus.
- Facet joints: The vertebrae are also joined
to each other by pairs of small joints which lie at the back of the
spine, one on either side. They can be affected by strain or by wear
and tear and may develop bony swellings, causing pressure on nerves.
- Network of nerves: The nervous system resembles
a telephone network carrying messages from your brain to various parts
of your body and back again. Messages that pass down the nerves make
muscles contract and so control movements such as walking. Those travelling
up the nerves carry sensations which eventually reach your brain so
that you experience sensations such as touch and pain.
- The spinal cord and nerves: A ‘cable’ of
nervous tissue, known as the spinal cord, extends from the brain down
the spine inside the canal formed by the vertebrae. The nerve roots
separate from the spinal cord, run for short distances within the canal
itself and emerge in pairs, one on each side, from the sides of the
vertebral column to supply the body, the arms and the legs.
The
spine – side view
Viewed from the side the human spine has a definite curve. The
spine is not a rigid structure; it is able to bend and flex because
there are cushions or discs between each of the vertebrae. The vertebrae
attach to the skull at the top and the pelvis at the bottom. |
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The
spine – back view
Viewed from the rear the human spine consists of a vertical column
of bony blocks called vertebrae, which sit one on top of another.
The vertebrae are numbered in descending order according to their
location: |
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The vertebrae
are separated from one another by flexible intervertebral discs.
Each disc is a flat, biscuit-shaped structure with a jelly-like
centre (nucleus) and an extremely strong outer skin (annulus).
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A cable
of nervous tissue, known as the spinal cord, connects the nerves
of the limbs and torso to the brain. The spinal cord runs through
a protective canal within the bony vertebral column. Nerve roots
emerge in pairs from the sides of the vertebrae. |
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What happens in back injuries
The fact that the spinal cord carries messages to and
from the body means that, if it is damaged, the ‘connection’ may
be affected, which can lead to the loss or alteration of sensation, development
of pain and weakness of movements. This is what happens when people become
paralysed after a serious accident.
The number of limbs paralysed, i.e.
whether they can move their arms and not their legs, or whether all four
limbs are paralysed, depends on where the spinal cord has been damaged.
If
the injury is in the neck, paralysis and loss of sensation can affect
both the arms and the legs. However, if the injury is in the thoracic
or lumbar segments – below arm level – then
only the leg muscles are affected. Fortunately most back problems damage
only the nerves and not usually the spinal cord.
Pain can develop in the
back itself, resulting from direct injuries to ligaments, tendons, joints
and other structures. As the same nerves that supply these tissues in
the back also supply the legs, patients may feel the pain as though it
were arising from the legs.
In addition, there may be pressure directly
on the nerves, producing pain, alteration in the sense of feeling and
weakness in the legs.
It is clear that the back is a very complicated
structure. When there has been some injury, back pain can arise for several
different reasons. Very careful analysis would be necessary to determine
what has happened in any individual. Fortunately, most acute episodes
of back pain get better without the need for specific forms of inter-vention.
As
a result very detailed tests to determine the particular injuries causing
problems are generally not required. However, when symptoms are more
serious and prolonged, it becomes important to determine exactly what
is going wrong. Very careful examination and diagnostic tests, including
some of the newer forms of imaging, may then become necessary.
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KEY POINTS
- The vertebral column consists of vertebrae joined
by discs and facet joints. The disc has a jelly-like central nucleus
and an extremely strong outer skin, the annulus
- Pain may arise from damage to a wide variety of
structures
- The pain is transmitted by the nerves. The ways
that these are stimulated are complex and depend upon the particular
tissue or type of nerve that has been affected
- As most acute episodes of back pain get better
quickly, usually there is no need for very detailed tests to determine
the precise cause
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