 |
Anatomy of Back Pain
Introduction to the Facet Joints |
|
| In the diagram below, a single vertebra is shown –
both from the top (dorsal, or plan view) and from the rear (posterior view). The articular
processes can be clearly identified: |
|
|
Two of the four processes extend upwards, from the top
of the laminae (termed superior) and two extend downwards from the bottom (termed inferior).
In the following diagram, the face of each, articular, process is marked with a blue
ellipse. The superior faces are marked in light blue; the dotted line indicates that the
face is hidden (or behind the part of the vertebra that is visible): |
|
|
Note: In the lateral view (on the right hand
side), only two of the four processes are visible. The right superior, and right inferior,
faces are marked.
The next diagram indicates how the articular processes of the lumbar vertebra L2, join
together with those of its neighbours, L1 (above) and L3 (below): |
|
|
Note: This diagram serves as a generic example.
The same, basic principles apply to the cervical and thoracic vertebrae.
The superior processes of L2 extend upwards and join with the inferior processes of L1
(directly above it); similarly, the inferior processes of L2 extend downwards and join
with the superior processes of L3 (directly below it).
The joints that are formed in this way are known as facet joints, because the faces
of the vertebral processes come together – contrast this, for example, with the hip
joint, which consists of a ball and socket.
Like other joints in the human body, the articular surfaces of the facet joints are
covered in a layer of smooth cartilage (designed to reduce friction and absorb shock). The
joint is lubricated by synovial fluid (similar in appearance and consistency to uncooked
egg white), and stabilised by a series of strong ligaments which surrounded the joint
capsule.
The facet joints are incredibly important to the mechanical function of the spine –
they lock the vertebrae together to form the spinal column, which in turn supports the
body. However, the faces of each joint can move relative to one other – for example,
by pivoting; or by sliding towards, or away from, each other.
Because of this, the vertebrae themselves are allowed to move – as a result, the
spine not only provides structural support, it is also flexible (allowing us to bend over
and rotate). The diagram below shows what happens when we bend over – either
backwards (extension) or forwards (flexion): |
|
|
The joints that are formed in this way are described as
articulated – that is, they lock the bones together, whilst allowing for
movement. An articulated lorry provides a useful analogy.
Given their importance to the mechanical function of the spine, it is not surprising that
the facet joints play an equally important role in the mechanical dysfunction of
the spine. In actual fact, compression of these joints (more commonly referred to as
compression of the spine), is responsible for the vast majority of back pain.
Next >>> Compression of the Facet
Joints
|
|
|
|
|
