Facet joints

Facet jointsFacet joints

Facet joints – the joints between the vertebrae

The spinal column consists of 33 bones on top of each other, called the vertebrae.

It consists of 4 regions:

  • cervical (neck) – 7 vertebrae
  • thoracic (chest) – 12 vertebrae
  • lumber (lower back) – 5 vertebrae
  • sacral (pelvic) & coccyx (tail bone) - 9 fused vertebrae

With the exception of the two top cervical vertebrae, each vertebra consists of the vertebral body at the front and the vertebral arch at the back. These surround spinal cord. This is called the vertebral canal.

The spine itself is supported by muscles, intervertebral discs, ligaments and facet joints.

Each vertebra consists of two parts, the vertebral body and the vertebral arch. The vertebral arch faces the back of the body. Above and below each vertebra are the facet joints.

The articular (joint) surfaces of the facet joints are about 1.5 cm wide and high and have a slightly oval shape. They are covered by a thin layer of cartilage and are surrounded by connective tissue. On the inside of this capsule, as in all other joints too, there is a mucous membrane that forms the inner lining of the joint, the synovial membrane. The function of this is to lubricate and supply nutrients to the articular cartilage.

The illustration below on the left shows the lumbar region seen from the side. The abdomen is to the right of picture, the back to the left. The joints between the vertebrae (facet joints) are shown in pink.

Facet joints – the joints between the vertebraeFacet joints – the joints between the vertebrae
Facet joints – the joints between the vertebraeFacet joints – the joints between the vertebrae

Function of the facet joints

The function of each facet joint is to guide and limit the movement of each spinal section. It protects and motion from excessive rotation and flexion.  The tough fibrous ring that surrounds it enables the disc to absorb and transmit the forces that act on it. Facet joints bear up to 20% of the forces that act vertically on the spine.

Illustration on the left: the upper figure shows the facet joints seen from the side, the lower figure shows them from behind. The facet joints (shown in pink) are formed by the superior and inferior articular processes on the vertebral arches. They are arranged in pairs on the left and right sides.

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