Facet Hypertrophy is the term used to describe a degeneration and enlargement of the facet joints. The facet joints, which are a pair of small joints at each level along the back of the spine, are designed to provide support, stability, and flexibility to the spine.
The facet joint may become enlarged as part of the body's response to degeneration of the spine, i.e. to try to provide additional stability to counteract the instability from degenerative disc disease.
The joint can enlarge to the point where it puts pressure on the adjacent nerves in the spine, which in turn can cause pain to radiate along the path of the nerve (e.g. sciatica).