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Anatomy of Back Pain
Compression of the Facet Joints |
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In the previous section, we saw how the facet joints of
the spine lock the vertebrae together, whilst allowing for a complex range of movements
– for example, the joints allow us to bend forwards (flexion), backwards (extension),
and to the side, and they also allow us to rotate (either clockwise or anti-clockwise).
However, if the joints become compressed (for example if the faces slide too far towards
each other), the vertebrae can no longer move freely. In turn, this prevents us
from moving freely – put simply, we become stiff (one of the primary symptoms of back
pain): |
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The compression of these joints can lead to many other
symptoms of back pain. For example, the cartilage on the articular surfaces of the joint
can start to wear – this tends to prevent articulation, increasing the level of
stiffness (ultimately, it can lead to spinal
osteoarthritis).
Compression also reduces the space between the vertebral bodies. Initially, this causes
the discs to bulge; if the pressure becomes too great, the discs eventually rupture, or
herniate: |
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When this occurs, the soft, inner core of the disc (the
nucleus pulposus) spurts out through a tear in the hard, outer layer (the annulus
fibrosis). This can be very painful in itself, but, once free, the inner core often
increases the pressure on the nerves surrounding the spinal cord, leading to more pain.
The condition is often referred to as a slipped
disc.
If we examine the way in which the nerves of the spinal cord exit the vertebral column, we
can also identify a third cause of pain resulting from compression of the facet joints
– direct, nerve root compression.
Individually, each vertebra in the spine has a hole in its centre – something
referred to as a vertebral foramen. When the vertebrae are stacked on top of one another,
the holes (or foramina) line up to form the spinal canal, through which the spinal cord
passes.
However, when two vertebrae come together, a hole is also formed in the side of the
spinal column – this is absent in the individual vertebra, and is known as an intervertebral
foramen. The nerves that branch off the spinal cord, exit the vertebral column via these
holes: |
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| Now, if the facet joints become compressed the
intervertebral foramen becomes smaller – this reduces the space around the nerves
that exit through these holes and can lead to nerve root compression (a condition known as
impingement). |
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So, facet joint compression leads to at least three
causes of back pain: spinal osteoarthritis; bulging and herniated discs; and nerve root
impingement.
At the most basic level, all back pain is caused by damage to the nervous system
– the nerves simply produce pain in response to a harmful event (thereby alerting the
body to the problem). But, because the nervous system is responsible for many other
activities, the effects of facet joint compression are very wide ranging – it can
also lead to referred pain (e.g. sciatica),
organ dysfunction and various other effects (e.g. pins and needles), as well as aggravating a whole host of bone
conditions.
Next >>> Introduction to the
Nervous System
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