What is the purpose of the facet joints in the spine?

The facet joints, which are located between the vertebrae in the spine, serve to limit excessive movement and protect the intervertebral discs. As the text states, "Their purpose is actually to limit movement because our discs, most of us are familiar with this, the anatomy we have, the outer kind of annular fibers, and then we have the inner gel center, that nucleus propulsus. And when we get a bulging disc, a herniated disc, what has actually happened is some of the angular fibers have ruptured and that nucleus has started to migrate."

The facet joints help prevent too much twisting or extension, which could further damage the outer annular fibers of the discs. If the facet joints did not limit motion, there would be increased risk of disc herniations. So in summary, the purpose of the facet joints is to limit vertebral movement in order to reduce mechanical stress on the intervertebral discs.