They are found at every spinal level, except at the top level of the cervical spine. Facet joints are encased with facet joint capsules, which contain fluid that protects and lubricates the joints. The posterior paired facet joints act with the anterior disc space to create a three joint complex at every level of the spine. This complex of joints allows for flex/extension, rotation and lateral bending.
Facet joints are in almost constant motion and quite commonly wear out or become degenerated. When facet joints become worn or torn, the cartilage may become thin or disappear and there may be a reaction of the bone of the joint underneath, producing overgrowth of bone spurs and an enlargement of the joints. The nerve root runs directly under the facet joint, and as it becomes enlarged it can pinch the nerve root (spinal stenosis).