Facet joints
The facet joints are probably the primary sites of pain in 10-15% of patients with
pathological low back pain. Facet joints, as you know by now, are the areas where one
vertebra connects with its counterpart above and below. As a person ages or applies
abnormal forces to his or her spine, the intervertebral discs gradually degenerate,
diminishing in size, bulging at the periphery and becoming stiffer. These degenerative
changes place additional stresses on the supporting structures of the vertebral bodies
such as the facet joints, ligaments and joint capsules and leads to osteoarthritis of the
spine. Continuous friction and pressure leads to irritation of the facet joints. This results
in:
Synovial and capsule enlargement – The facet joints are covered and protected by
fibrous tissue capsule and a thin membrane called synovial membrane. The
synovial membrane lines the inside of the capsule and secretes a lubricating fluid
which makes movement at the joint much smoother. When there is inflammation
or irritation of the joint as can happen in arthritis, more synovial fluid is released
into the joint space as a reaction to the inflammation. This stretches the nerve
endings thus causing pain during movement or even at rest.
Bone spurs – Bone reacts by thickening at the site of irritation or inflammation.
Thickening of bone at the ends leads to protrusion of bone beyond the joint area.
These protrusions are called spurs. Bony spurs at facet joints may protrude
inwards and narrow the spinal canal – a condition known as spinal stenosis.
Spurs may also protrude outside and impinge on nerve roots coming out of the
intervertebral foramina. In both cases, pressure on the spinal cord or nerve roots
causes back pain and/ or leg pain.