Facet Arthrosis (degeneration)
The wear and tear or degeneration that can occur in a joint is often referred to as arthrosis. The facet joints in the back part of the spine, which are joints that normally have a smooth cartilage surface, can wear out.
While the disc is the cushion in the front, the facet joints in the back part of the spine glide over each other as the spine moves, with the center of rotation in the region of the disc.
In this cross sectional view, normal appearing facet joints are seen. Notice that it appears that the two sides fit nicely together.
In this view of a level with facet degeneration, it can be seen that extra bone is seen forming on one side, and extra fluid is seen onthe other. Clearly, these joints don't seem like they'd have smooth motion as the spine flexes and extends.
Here in various CT scans, which highly bony details better than an MRI, the joint space can be seen as being almost the same thickness throughout at a level without wear and tear of the facet joints on this cross sectional view.
In this image, however, the facet joints can be seen as irregular and rougher appearing, and on the right side, there is extra bone growth, referred to as osteophytes, which are a sign of arthritis of these joints.